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Pump and Motor Operation

Glossary of Pump and Motor Terminology

In electrical terms, a motor is a machine for converting electrical energy into mechanical energy.

You need to be familiar with the terminology used in context with motors and pumps:

Air gap The air space between two magnetically related or electrically related parts - for example, the space between poles of a magnet or the poles of an electric motor.
Alternating current An electrical current that alternates, flowing first with a positive polarity, followed by a negative polarity.
Capacitor An electrical device consisting of two or more conducting plates separated from one another by insulating material and used for storing an electrical charge.
Dielectric The insulating material that separates and insulates the conducting plates in a capacitor. It can be a gas, liquid, plastic, glass, paper - or a combination.
Dielectric breakdown The failure of an insulating material to separate electrical charges. Breakdown occurs when the insulating material changes and conducts the electrical charge between plates.
Frequency In electricity, the number of times alternated current changes direction during one second. Frequency is measured in hertz (cycles per second).
Hertz A unit of measurement of frequency. Hertz indicates "cycles per second" of alternating current.
Horsepower The conventional unit of measure foi- power, this indicates the result of force multiplied by distance multiplied by time. One horsepower (hp) equals 746 watts, or 33,000 foot pounds per minute or 550 foot pounds per second.
Locked-rotor test A test of an electric motor in which the shaft is prevented from turning while power is applied. It can, for example, be used to determine fixed and variable losses in a motor.
NEMA The National Electrical Manufacturers Association.
No-load test Operating a motor at full speed with no load to determine rotational power losses.
Rotor The rotating part of an electric rotating machine. In a motor it is connected to and turns the drive shaft. In an alternator or generator it is turned to produce electricity by cutting magnetic lines of force.
Service factor A measure of the reserve margin built into a motor. Motors rated more than 1.0 SF have more than normal margin and are used where unusual conditions such as occasional high or low voltage, momentary overloads and so forth are likely to occur.
Single phase Having only one alternating current or voltage in a circuit.
Stator The stationary part of a motor that contains the laminated steel core with the winding; this is where the rotor revolves.
Torque A force that produces a rotating or twisting action.
Triac An electronic switch used in applications such as power switches, light dimmers and motor controls.
Voltage Electrical pressure; the force that causes current in an electrical conductor.
Watt A unit of electrical power representing the power developed in a circuit by a current of one ampere when the voltage drop is one volt.
Wattmeter An instrument for measuring electrical power.


Motor types
Capacitor-start motor An alternating current split-phase induction motor that has a capacitor connected in series with an auxiliary winding for starting. The auxiliary circuit disconnects when the motor is up to speed. This motor requires an internal starting switch and governor.
Permanent split capacitor motor A single-phase electric motor that uses a phase winding in conjunction with the main winding. The phase winding is controlled by a capacitor that stays in the circuit at all times and is rated for continuous running. The capacitor improves starting and running power factors. This motor does not require either an internal starting switch or a governor.
Split-phase motor (also known as a resistance start motor) A single-phase induction motor that has an auxiliary winding connected in parallel with the main winding. The auxiliary winding's magnetic position is not the same as the main winding, so it can produce the required rotating magnetic field needed for starting. This motor requires an internal starting switch and a governor.
Three-phase electric motor A motor that operates from a three-phase power source. In three-phase power, three voltages are produced that are 120 electrical degrees apart in time. This motor has no internal starting switch.
Two-capacitor motor An induction motor that uses one capacitor for starting and one for running. The starting capacitor is in parallel with the running capacitor as the motor is starting; at 75 percent of speed, the starting capacitor is cut out of the circuit. This type of motor is sometimes called capacitor start/capacitor run and requires an internal starting switch and governor.


Pool and spa pumps are classified as centrifugal pumps. That is, the centrifugal force that is created by spinning the water, will force the water downwards and if there is an opening or a hole, this water will get pushed forward through the hole.

The pump operates the same way. The impeller in the pump spins, shooting water out of it. As the water escapes, a vacuum is created that demands more water to equalize this force. Water is pulled from the pool or spa and sent on its way through the circulation plumbing. The hole size determines the amount of water and how fast it can escape. Also the various designs of impellers, diffusers, and volutes determine the same features in a pool pump, which is discussed later.

Pumps used for pools are self-priming, that is, they expel the air inside upon start-up, creating a vacuum that starts suction. Once water is flowing through the pump, if you close a valve on the outflow side of the pump, restricting all flow, maximum possible pressure is created. However, there is no destructive force created, the impeller simply spins in the liquid indefinitely.

Strainer Pot And Basket

The plumbing runs to the inlet port of the pump, from the pool or spa main drain and skimmer. The inlet is usually female threaded for easy plumbing.

Water flows into a chamber, called the strainer pot or hair and lint trap. This chamber holds a basket that permits water to pass but retains the debris. Generally the basket is 4 to 6 inches in diameter and 5 to 9 inches deep, and is made of plastic mesh. In some pumps the strainer pot bolts to the volute with a gasket to prevent leaks, while in yet others it is molded together with the volute as one piece. In bathtub spas or booster pumps, there is no strainer pot and basket at all since debris is not a problem.

There is an access provided to clean out the strainer basket, and also have cover that are usually made of transparent plastic and can easily be attached with a nut and a bolt. The strainer cover has an O-ring between the lip of the strainer pot and itself. This prevents any leakage due to suction. Also the pot has a small threaded plug that screws into the bottom. This plug is designed to allow complete drainage of the pot when winterizing the pump. It is made of a weaker material than the pot on metal pots, for example, the plug is made of plastic, soft lead, or brass. If the water in the pot freezes, this sacrificial plug pops out as the freezing water expands, relieving the pressure in the pot.


The volute, is the chamber in which the impeller spins, that forces water out of the pump and into the plumbing that takes the water to the filter. The outlet port is usually female threaded for easy plumbing. The movement of the impeller sucks the water from the pool through the strainer pot. The resulting vacuum in the pot is compensated for by water filling the void. The rushing water is contained by the volute which directs it out of the pump. Therefore the pot can be considered a vacuum chamber and the volute a pressure chamber.

The impeller by itself cannot create a strong vacuum by itself to make the water flow begin. The area immediately around the impeller must be limited to eliminate air and help start the water flow. A diffuser and/or closed-face impeller help this process, but in many pump designs, the volute serves this purpose. In some designs, the inside of the volute is ribbed to improve the flow efficiency.


The impeller is a ribbed disk that spins inside the volute. The disk is called a shroud and the curved ribs are called vanes. Water entering the center of the impeller, is forced to the outside edge of the disk by the vanes. As the water moves to the edge, there is a resulting drop in pressure at the center, creating a vacuum that is the suction of the pump. The amount of suction is determined by the design of the impeller and pump components and the strength of the motor that spins the impeller.

There are two types of impellers, closed-face and semi-open-face. In the closed-face impeller, the vanes of the impeller are covered in both front and back. Water flows into the hole in the center and is forced out at the end of each vane along the edge of the impeller. This type of impeller is very efficient in moving water and a diffuser is added to the design to slow the speed of the water before it leaves the volute. This design does not take into consideration the debris that might escape the skimmer and strainer basket and into the impellers. This led to the new design, the semi-open-face design allowing small debris to pass by actually pulverizing it. Diatomaceous earth is the chief cause of clogging in the impellers.

Impellers are rated by horsepower to match the motor horsepower that is used. This, in turn, determines the horsepower rating of the pump or pump and motor you have. Usually the motor is of higher horse power than the impeller.

Seal Plate And Adapter Bracket

The volute is divided into two sections, the rounded volute and the seal plate. This allows an access to the impeller. The seal plate is joined to the volute with a clamp or with bolts. An O-ring between them makes this joint watertight. The motor is bolted directly onto this type of seal plate. In other designs, the seal plate is molded together with an adapter bracket that supports the motor and bolts to the volute, with a paper or rubber gasket between them to create a watertight joint.

In both cases, the shaft of the motor passes through a hole in the center of the seal plate and the impeller is attached, threaded onto the shaft. The bracket allows access to the shaft extender for adjusting the clearance between the impeller and volute. The pump design of closed face needs no such adjustment, so the shaft need not be exposed.

Shaft And Shaft Extender

The shaft of the motor is the part that turns the impeller, creating water flow. The impeller needs to be adjusted in relation to the volute, so a shaft extender has been created. The extender, made of brass or bronze, slides over the motor shaft and is secured by three allen-head setscrews. The male threaded end of the shaft extender then fits through the seal plate and the impeller is screwed into place.

The extender is round with a flat area on two sides to prevent the extender from spinning when performing maintenance. Some designs require an O-ring near the threads of the extender to ensure a watertight seal. While other designs rely only on the pump seal.

The shaft should never be in contact with electric current, so most motor shafts today are designed with a special internal sleeve to insulate the electricity in the motor from the water in the pump.


The seal allows the shaft to turn freely while keeping the water from leaking out of the pump. If the shaft passed through the large hole of the seal plate without some kind of sealing, the pump would leak water and if the hole was made small and tight, perhaps of tight-fitting rubber, the high-speed spinning of the shaft would create friction and burn up the components.

The seal is in two parts. One half of the seal is composed of a rubber gasket or O-ring. This is fitted around a ceramic ring and fits into a groove in the back of the impeller. The ceramic ring can withstand high temperature caused by friction. The other half of the seal is made of a metal bushing and a spring. This fits into a groove in the seal plate. The end of the spring that faces the ceramic ring is covered with a heat-resistant graphite. Since the spring exerts pressure on both the sides it makes the whole seal water tight there by preventing the water from leaking out of the pump.

As the shaft turns, these two halves spin against each other but do not burn up because their materials are heat-resistant and the entire seal is cooled by the water around it. Therefore, if the pump is allowed to run dry, the seal is the first component to overheat and fail. Pumps are not designed to run without water for more than a few minutes while priming.


Motors are rated by horsepower. The most common ratings for pool and spa motors range from 0.5 to 2.0 horsepower. Electricity flows through the motor windings, which are thin strands of coiled copper or aluminum wire. The windings magnetize the iron stator. Using this concept, the rotor spins, turning the shaft. The shaft rides on ball bearings at each end. A built-in fan cools the windings because some of the electrical energy is lost as heat. The caps on each end of the motor housing are called end bells. A starting switch is mounted on one end with a small removable panel for connection and maintenance access.

The thermal overload protector, a heat sensitive switch that is like a circuit breaker, is mounted on the panel. If the internal temperature gets too hot, it shuts off the flow of electricity to the motor to prevent greater damage. As this protector cools, it automatically restarts the motor, but if the unit overheats again, it will continue to cycle on and off until the problem is solved or the protector burns out.

The capacitor of the motor is located on top of the motor housing in a separate box or housing. The capacitor, has a capacity to store an electrical charge and when discharged it gives the motor enough of a jolt to start. This way the capacitor can impart enough energy to start the motor and then run on a lower amount of electricity. A motor needs more electricity to start than to keep it going. Without the capacitor, the motor would need to be served by very heavy wiring and high-amp circuit breakers to carry the starting amps.

Some motors are designed to operate at two speeds, the normal rotation speed is 3450 revolutions per minute (rpm) and the low speed is 1750 rpm, depending on the need for circulation and heating or for jet actions (in spa).


The three main types of motors that you find in pool and spa are:


When the start up power requirements are low, the motor is usually 1/4-horse power or less. It also does not require any capacitor.

Capacitor start, induction run (CSI)

This is the most commonly used motor in the pool business. This motor uses a capacitor and starting windings to start up, then these are shut down and a running winding takes over. As noted previously, the capacitor and start-up windings allow faster, stronger torque to overcome the initial resistance of the impeller against standing water, then when the water is moving and less power is needed to keep it moving, the system shuts off and the lighter running winding takes over.

Capacitor start, capacitor run (CSR)

This is the concept of the energy efficient motor. The difference between a CSR and CSI motor is that the CSR motor employs a capacitor on the running windings as well. This smoothes out the variations in the alternating current (ac) power that helps reduce heat loss in the winding. In short, CSR motors are more efficient but cost more because of the added parts. These motors are also called switch-less, because on some designs the run capacitor makes a start switch unnecessary. These are the most energy efficient motors when they have heavier wire in the windings to lower the electricity wasted from heat loss. A good way to compare energy efficiency between two motors is to compare the gallons pumped to kilowatts used. The higher the resulting number, the more efficient is the pump and motor. Kilowattage is determined by multiplying amps by voltage.


Motors are most commonly designed to work on 110 or 220 volts. Higher horsepower motors might run on three-phase current. So it is best to get the work done by a certified electrician.

Housing Design

The variety of the motor are designed for pool pumps. The motor must be compatible to the pump design. The motor face could be C-frame or square-flange type, so check for the correct fit and compatibility with the pump.


The service factor of a motor is a multiplier number. When this number is multiplied with the horsepower rating of the motor, you get the real horsepower at which the motor is designed to operate on a continuous basis. As an example, a motor rated at 1 hp with a service factor of 1.5 can actually safely run a 1.5-hp pump (1.0 x 1.5 = 1.5 hp).


Here is the detail that you get from the nameplate on any motor:

Electrical specifications

A diagram showing how to wire the starting switch plate for 110 or 220 volt supply. If this diagram is not on the outside of the motor, remove the small access door in the end bell and it should be printed on a sticker in there. These stickers frequently come off as the motor gets older, so if no diagram is available, refer to the manufacturer's guidebook available at your supply house.

The nameplate also tells you of the maximum load or amperage. It might say "10.5/5.2." This means the start-up draw is 10.5 amps, and the normal running draw is 5.2 amps. Some times the manufacturers also mention the amps required to power the nominal horsepower as well.

The nameplate also lists the electrical phasing and cycle frequency in hertz. Alternating current in the United States runs on 60 hertz. In Europe it is 50 hertz, and that's why you can't use some appliances from one country in another, even with a voltage converter.

Manufacturer and date

The manufacturer's name appears on the rating plate, along with the model and serial numbers, and includes the day, month, and year the motor was built.


The relative strength of the motor is expressed in horsepower and corresponds to the specifications of the pump that is to be driven by the motor.


A diagram of the wiring connections is printed on the name-plate. There will also be a few words about mounting, such as "mount horizontally" or "mount with vents down."

Duty rating

Pool and spa motors are designed for continuous duty, meaning they can run 24 hours a day for their entire service life without stopping. The nameplate shows this by the rating "Continuous Duty." The horsepower, service factor, rpm, and frame style of the housing are listed. If the motor has a thermal overload protector, the nameplate will indicate it.

Other information is also shown on the nameplate, such as the starting method (C means capacitor for example), the insulation category, a rating of UL (Underwriter's Laboratory) or CSA (Canadian Standards Association) approval, and ambient (surrounding) temperature requirements.

Horsepower And Hydraulics Equals Sizing

To find the correct horsepower of the motor or the pump, that is required for the job, it is best to consider the needs of the pool and spa, hydraulics involved and the horsepower of the equipment. This gives you the right size of the unit that needs to be installed.


The study of water flow and the factors affecting that flow is Hydraulics. It is important to understand because its principles affect plumbing and equipment sizing choices for there are so many factors involved.

Terms commonly used

Head and Flow rate Head is the resistance of water flow through plumbing and equipment expressed in feet. The lower, the better. Flow rate is the volume of water moved in a given period of time.

As the length of the plumbing pipe increases the resistance will bring down the flow rate.The additional resistance (head) of that added pipe means that the pump cannot push the water as fast. This loss of flow, as head increases, is called head loss, a somewhat deceptive term because it is actually flow that is lost. The term actually means flow loss caused by head increase. If you continue to increase the head (resistance) by adding more vertical pipe, the flow rate will continue to decrease until at last, no water comes out at all. This pump can now be charted on a graph, allowing you to study its performance characteristics. On the left side of the graph is the possible feet of head, from 0 to 10 feet. On the bottom is the possible flow rate, from 0 to 10 gpm. By finding where the head and flow rates intersect, you can create a pump curve for your pump.

Because you generally have no way to measure these factors, the manufacturer provides a pump curve for each pump. If you know the amount of head (resistance) in your pool or spa system and you know the desired flow rate, then you can determine which pump will satisfy those needs by referring to the manufacturer's pump curves.

Pumps are designated low, medium, high, or ultra-high head. The higher the head designation, the less strain is placed on the pump and motor components: Low head-suck well; push poorly; Medium head-suck well; push well; High head-suck poorly; push well (most common in pools and spas); Ultra-high head-suck poorly; push well (pool sweeps).

One factor affecting which type a particular pump will be is its impeller. Thin vents on the face (closed or semi-open) result in greater push but poor suck; in other words, poor self-priming capabilities but good circulating flows.

Suction head, so far discussed, is the head created by adding resistance to the outflow side of the pump. By restricting the intake or requiring the pump to lift water from a source below it, you also create head. This is called suction head, sometimes called vertical feet of water. Each foot on the suction side equals a similar foot on the discharge side, called discharge head. The only thing to remember here is that head (resistance) is created on both sides and must be calculated when determining pump size.

Dynamic and static head Up to now the static head or the head created by the weight of standing (static) water is described. This is only a small portion of the total head in the system. The rest is created by the friction of water flowing through the entire system, called dynamic (moving) head. The diameter of the pipe and the speed of the water determines how much resistance is created by friction. Further friction is created when water must go through or around other obstacles, such as through the filter, heater, solar panels, and plumbing fittings for every plumbing elbow or bend creates head too.

Cavitation refers to the vacuum created when the outflow capacity of a pump exceeds the suction intake. This happens, for example, when a pump is oversized for the suction line or when the distance from the body of water is too far. The result is bubbling and vibration.

Total dynamic head (TDH) is the total of plumbing and equipment head for the entire system. Vacuum head (suction) plus pressure head (discharge) equals total dynamic head.

Shut-off head The amount of head at which the pump can no longer circulate water. It is 0 gpm.

Calculations Here are a few general numbers to use in your calculations.

Pipefittings, To make it easier to calculate head in your plumbing system, it is measured for every 100 feet of pipe or the equivalent. Plumbing connections, fittings, and valves have different amounts of resistance than straight pipe, so these must first be converted to the equivalent length of straight pipe. Unions and straight connectors act like additional lengths of straight pipe, so no special calculations are needed. Going around corners is what creates head. Here are the values for the most common PVC fittings you will use:

  • 1/2-inch x 90-degree elbow = 7.5 feet of straight 1/2-inch pipe
  • 2-inch x 90-degree elbow = 8.6 feet of straight 2-inch pipe
  • 1/2-inch x 45-degree elbow = 2.2 feet of straight 1/2-inch pipe
  • 2-inch x 45-degree elbow = 2.8 feet of straight 2-inch pipe

It is interesting to see that three times as much resistance is created when a 90-degree fitting is used instead of a 45. That is particularly significant, because there are times when you have a choice between using two 45-degree fittings in a job rather than one 90. The combination of two 45-degree fittings creates less resistance than one 90. Also note that in a T fitting, the turn around its 90-degree bend is sharper than the more gradual sweep through 90 degrees created by a typical 90 fitting. Thus, more resistance is created in a T fitting, even though the water is being bent 90 degrees in either case.

Filters create 5 to 7 feet of head. The manufacturer will tell you in the literature that accompanies the product how many feet of head the unit creates. You can also measure the amount by placing a pressure gauge on the pipe leading into the filter and one on the pipe going out. The difference, measured in pounds per square inch (psi), tells you the feet of head. As dirt builds up in a filter, however, head increases. A clean filter will have no more than 3 psi difference between the input pressure and the output pressure. Since 1 psi equals 2.31 feet of head, a new, clean filter should add no more than 6.9 feet of head.

Manufacturers recommend cleaning a filter when the operating pressure (as read on the pressure gauge, expressed in psi) builds up to more than 10 psi over clean operating pressure. Since 10 psi equals 23.1 feet of head, you can see that the resistance caused by dirt added to the normal amount of head for the filter itself can total over 30 feet of head for this component alone. This is another factor why providing a slightly larger horsepower pump than required on a system is a good idea.

Heaters create 8 to 15 feet of head. Like filters, the manufacturer will tell you in the literature that comes with the unit what the head loss is for the unit at a given flow rate. Also like filters, as scale builds up in the heat exchanger, more friction is created and therefore more head. This is another good reason to beef up your pump when doing the sizing calculations for an installation.

Poolside hardware Main drain covers, skimmers, and return outlets all add head. To know exactly how much, you must refer to each manufacturer's specifications. A general rule of thumb is to add 5 feet of head to allow for the total of such components in your system.

Pumps Pumps also create head, but the manufacturer's charts allow for this, so your calculations need not consider it. When you look at the TDH for the system on the pump curve, the pump head loss is already figured in the performance ability.

Turnover rate The turnover rate of a body of water is how long it takes to run all the water through the system. It is desirable for the water to completely circulate through the filter one to two times per day, but local codes generally require a specific time period. In Los Angeles, for example, it is 9 Pools must turn over in 6 hours, Spas must turn over in 1/2hour, and Wading pools must turn over in 1 hour.

Various components offer more or less resistance at different speeds expressed in gallons per minute. To calculate the TDH of a system, you must know that speed. To decide what speed is needed (and therefore what size pump is needed to deliver that speed in your system) you must establish a turnover rate.

Let's say if you've calculated the volume of water in the pool as 18,000 gallons.

18,000 gallons / 6 hours = 3000 gallons per hour 3000 gph / 60 minutes = 50 gpm

Therefore, you need a pump capable of delivering a flow rate of 50 gpm under the TDH of the system. The manufacturer's pump curves described previously will tell us which pump can do this.

Methods of calculating TDH Here are the three methods for calculating TDH.

Method 1: Exact values:

If you have the exact specifications of the pool as built or as proposed, measure all the pipe from the pool, through the equipment, and back to the pool. Add the equivalent feet of pipe for all the fittings. Add the feet of head at the desired flow rate for the filter, heater, and any other components to arrive at the TDH for the system.

Method 2: Estimated values:

  1. Suction-side head. Assume 2 feet of head for each 10 feet the equipment is away from the pool.
  2. Discharge-side head. Estimate how many feet of pipe are in the system back to the pool. Double that estimate to allow for fittings.
  3. Using the tables, calculate the feet of head for the total amount of pipe on the discharge side.
  4. Equipment head. Consult manufacturer's tables and charts for the desired flow rate (in the example, 50 gpm).
  5. Add these three parts together to get the TDH.

Let's try a simple example. Let's say our equipment is 30 feet from the pool (at 2 feet of head per 10 feet of distance, that makes 6 feet of head). There is about 60 feet of 1/2-inch plumbing between the equipment and the run back to the pool (doubled is 120 feet). The table says 13.5 feet of head per 100 feet of pipe equals 1.2 x 13.5 or 16.2 feet of head. The filter manufacturer says our sample filter has 7 feet of head; the heater manufacturer says 15 feet of head. Therefore:

  • Suction side estimate 6.0 feet
  • Discharge side estimate 16.2 feet
  • Main drain and skimmer estimate 5.0 feet
  • Filter 7.0 feet
  • Heater 15.0 feet for a total dynamic head of 49.2 feet.

Now you can consult various manufacturer's pump charts to decide which pump will deliver the desired 50 gpm at 49.2 feet of TDH.

Method 3. Measured values:

An easier and more accurate way to estimate all of this, if the existing pump is operating, is to measure the vacuum on the suction side of the pump and the pressure on the discharge side. Plumb a vacuum gauge on the pipe entering the pump. It measures inches of mercury. Every 1 inch of mercury equals 1.13 feet of head. Plumb a pressure gauge on the pipe coming out of the pump. It measures pounds per square inch (psi). Every 1 psi of pressure equals 2.31 feet of head.

Multiply the gauges out accordingly and the sum of the two gives you the TDH of the system. This might sound like work, plumbing in two separate gauges, but it really isn't, and it gives you the most accurate TDH calculation because it takes into account the dirty filter, the limed-up heater, all the unseen plumbing. It also allows you to keep an eye on the TDH in the system at any time and more easily troubleshoot poor performance in the equipment.


The running water not only encounters friction created by pipes and equipment, but the water itself is creating friction. This friction will strip copper from pipes and heater components causing all kinds of havoc,9see the section on chemistry, damages filter grids, and makes DE or sand inefficient (see the filter section).

Because of this, most building codes set maximum flow rates of 8 feet per second through copper pipe and 10 feet per second through PVC. Since heaters all use copper heat exchangers, use 8 feet per second even if the plumbing is PVC. Los Angeles County, for example, allows a maximum flow rate of 8 feet per second on suction pipes of any type. What is feet per second in terms of gallons per minute?

50 gpm in 1 1/2-inch pipe = 7.9 feet per second

50 gpm in 2-inch pipe = 4.8 feet per second

60 gpm in 1 1/2-inch pipe = 9.5 feet per second

60 gpm in 2-inch pipe = 5.7 feet per second

By the way, there are a few exceptions to the rules. Los Angeles County requires pumps to deliver the desired gallons per minute at 60 feet of head. When sizing pumps, you must assume at least 60 feet of head regardless of the actual calculations. In filters, on the other hand, you must use the actual head as measured. Altitude also affects these calculations. Over 3300 feet above sea level a motor runs hotter, so you will want to upgrade to the next horsepower.

Maintenance And Repairs

It is always better to keep the pump and the motor in good condition for they affect the efficiency of the system. Keep the motor in good working condition by keeping it dry and cool. Also do not allow the bad and worn bearings take toll on the motor. Attend to any leaks as soon as detected in the pumps as they will eventually affect the motors.

The basic repairs and maintenance of the pump and motor unit are discussed in the following sections.

Strainer Pots

When the strainer basket get clogged with debris and dirt clean it out for this is one sure maintenance procedure required for pump maintenance. Even small amounts of hair or debris can clog the fine mesh of the basket and substantially reduce flow. For this, you have to shut down the system, remove cover bolts or clamps, clean out hair and filth from the basket, put the basket back, find a water source to fill the pot so the pump will reprime easily, check the O-ring, replace the cover, tighten the bolts or clamps, and restart the system.

Breakage is the other problem encountered at the strainer pot. If the basket or the pot is broken or cracked, the basket will permit large debris and hair to clog the impeller or the plumbing between the equipment components.

Gaskets And O-Rings

Most problems occur in strainer pots when the pump is operated dry, due to which the case heats up, with no water to cool it. The strainer basket will melt; the pot cover, if plastic, will warp; and the O-ring will melt or deform. Replacement of the parts should be done in such cases.


When gaskets leak, the replacement process is the same as same as removing the strainer basket. Remove the strainer pot. Clean out the old gasket thoroughly with no residual remains. Reassemble the new gasket and strainer pot the same way the old one came off. Tighten the bolts evenly. Sometimes the bolts are designed to go through the opening in the pot and volute and are tightened with a nut and lock washer on the other side. Be careful in assembling these components.


When removing and replacing the strainer pot cover, be sure the O-ring and the top of the strainer pot are clean, because debris can cause gaps in the seal. Sometimes these O-rings become too compressed or dried out and brittle and cannot seal the cover to the pot. Replace the O-ring in such case.

Changing A Seal

All pumps have seals to prevent water from leaking out along the motor shaft. When these wear out due to overheating, they are easy to replace. The first thing to do is to turn off the electricity to the motor at the breaker.

  1. To access this seal for replacement, remove the four bolts that hold the pump halves together, it is not necessary to remove the entire pump from the plumbing system.
  2. Grasp the motor and pull it and the bracket away from the volute. Wiggle it slightly from side to side as you pull back to help break this joint.
  3. Take your pliers or a wrench and hold the shaft extender to prevent it from turning. Unscrew the impeller from the shaft extender using an impeller wrench. You can also wrap a rag over the face of the impeller so you don't cut yourself and twist it off by hand. As a last resort, hold a large screwdriver against the impeller and tap it gently with a hammer. Use care not to damage the impeller. Use even more care that the screwdriver doesn't slip and damage you.
  4. Remove the four bolts that hold the bracket on the motor. If needed use a hammer to gently tap the bracket away from the motor.
  5. Remove both halves of the old seal. Note how each half is installed so you get the new one back in the same way. One half is in the back of the impeller and is easily popped out with a flat-blade screwdriver. The other half is in the seal plate and motor bracket unit. Lay the bracket on your workbench with the seal on the bottom. You will see the back of the seal through the hole in the seal plate. Using the flat-blade screwdriver once again-put the tip on the back of the seal and tap it with a hammer. It will pop out easily.
  6. Install the new seal. First, look up your pump in the manufacturer's literature or supply house catalog to determine what model seal you need. Failing that, you can take the old one to the supply house so they can identify it for you. There are only three commonly used seals in pool and spa work. Clean out the seal plate and impeller where you have just removed the old seal. Use an emery cloth or a small wire brush and water. Dry each area and apply a small amount of silicone lubricant to help the new seal slide into place. Install each half of the seal the same way you removed the old one-white ceramic of one half facing the glazed carbon ridge of the other half.
  7. Gaskets. When you break apart a pump, the old gasket usually won't reseal. Clean all of the old gasket off of the seal plate and volute. Scrape it clean if needed with flatblade screwdriver. Now reassemble the pump the same way you took it apart, placing a new gasket between the pump halves.
  8. Check for leaks by starting the pump and let it run several minutes. A fresh paper gasket might leak for a few minutes until it becomes wet and swells to fill all the gaps, but it should stop leaking after a short time. If your job does leak, take it apart and go over each step again, making sure the seal halves are seated all the way and that there is no corrosion or debris left in the impeller or seal plate that might prevent the new seal from seating completely.

In some pumps where the parts are assembled differently, you follow the same steps. The clamp is removed to disassemble the pump halves, and you must remove the diffuser to get to the impeller. To remove the impeller you can grip it with your hand and twist it off, but the trick with these units is to stop the shaft from spinning as you twist off the impeller. There are air vents in the motor on the end closest to the pump itself. Look in and you will see the motor shaft. Place a flat-blade screwdriver in one of the air vents and wedge it against the shaft to keep it from turning.

Alternatively, you can remove the end cap and look inside as you twist the impeller. You will see the back end of the shaft, with the start switch attached. Since this switch is fragile, you must remove it (one screw) to access the slotted screw in the back end of the shaft. Place the screwdriver in this screw to keep the shaft from turning as you remove the impeller.

Instead of a gasket, some pumps use an O-ring. Clean this and lubricate it with silicone before reassembly. If it has stretched and it seems like there is too much O-ring for the channel in the volute, try soaking the gasket in ice water for a few minutes to make it shrink a bit.

Some pumps use a plastic impeller with a housing that holds half the seal in place. if the pump has run dry and overheated the pot, this housing might be warped and the seal will not fit tightly. The only solution is to replace the impeller. This is a common problem with automatic cleaner pumps, which are not self-priming.

Remember to use only non-hardening silicone lube on all pool and spa work. Vaseline or other lubricants are made of petroleum, which eats away some plastics and papers.

Pump And/Or Motor Removal And Reinstallation

Sometimes it is necessary to remove an entire pump and motor unit to take it apart or complete a repair. If the pump is damaged beyond your ability to repair it, you might want to take the entire unit to a motor repair shop. They can rebuild it as needed, and you can reinstall it.

Generally, to remove the pump and motor as a unit first thing is to turn off the circuit breaker. Now you will need to cut the plumbing on the suction and return side of the pump. Leave a few inches on both the sides of the cut to replumb it by slip couplings.

When installing or reinstalling the plumbing between the pump and filter keep bends and turns to a minimum. Also, do not locate the pump close to the base of the filter. When you open the filter for cleaning, water is sure to flood the motor. Lastly, try to keep motors at least 6 inches off the ground, to prevent it from flooding during rains.

The electrical connection must be removed before the pump and motor can be disengaged. Now remove the access cover to the switch plate area of the motor, near the hole where the conduit enters the motor. Remove the three wires inside the motor and unscrew the conduit connector from the motor housing. Pull the conduit and wiring away from the motor and the entire pump and motor should be free.

If there is an additional bonding wire (ground wire), it can be easily removed by loosening the screw or clamp that holds it in place.

Tape off the ends of the exposed wires, and leave a note on the breaker box, as a warning.

New Installation

Position the pump as close to the body of water and as near to water level as possible so it doesn't have to work so hard. Mount the unit on a solid, vibration-free base. Make sure there is adequate drainage in the area so that when it rains or if a pipe breaks the motor won't be drowned. Bolt or strap down the pump.

Plumb in both suction and return lines with as few twists and bends as possible, to minimize head. A gate valve on both sides is advisable to isolate the pump when cleaning other components. A check valve is essential if the unit is well above water level. Plumb the unit far enough away from the filter that it won't get soaked when you take the filter apart.

Replacing A Pump Or Motor

Having learned how to remove and break down a pump and motor in the previous sections, replacing any of the components is simply a matter of disassembling the pump down to the component that needs replacement, getting a replacement part, and reassembling the unit. Of course, if the entire pump and motor is to be replaced, you purchase the replacement as a unit and plumb it in as previously described.

Sometimes the motor will trip the circuit breaker when you try to start it. If this happens it is usually because there is something wrong with the motor; however, it could be a bad breaker or one that is simply undersized for the job and has finally worn out. To replace the motor here are the procedure:

  1. Break down the unit as described in the section on changing a seal. Remove the shaft extender by removing the allen-head setscrews and pulling the extender off the motor shaft. Sometimes this might need persuasion. Use your large flat-blade screwdriver to pry the extender away from the motor body. Sometimes corrosion will eat away at the setscrews and extender-if it is too tough to remove, replace it.
  2. Before sliding the shaft extender on the new motor, clean the motor shaft with a fine emery cloth such as you might have in your copper pipe solder kit. Apply a light coat of silicone lube to the shaft. When you put the extender on the motor shaft, the setscrews go into a groove that runs along the shaft. This groove allows the screws to grip and not slide around the shaft.
  3. Now slide the new extender in place, lining up the setscrews along the channel, but do not tighten the setscrews. When you have reassembled the bracket and seal plate, seal, and impeller, you can adjust the impeller to just barely clear the seal plate face, then tighten the setscrews. Be sure the impeller is screwed tightly onto the shaft extender before making this adjustment. If it is loose, when the motor starts it will tighten the impeller, by turning it tighter against the extender, thereby tightening it against the seal plate, seizing up the unit.
  4. Secure the shaft extender with your pliers or 3/8-inch box wrench and lay a rag over the impeller. Firmly hand tighten it. Reassemble the remaining pump parts and/or replumb the entire unit back into place.
  5. You can access the electrical connections through the switchplate cover in the front end bell.

Troubleshooting Motors

The first and most common motor problem is water, which may be due to on of he many reasons, like rain, filter cleaning or breaking of the pipe. In all cases, dry the motor and give it 24 hours to air dry before starting it up. Even small amount of moisture can short the motor. The basic problems beyond this are as follows.

Motor will not start

Check the breaker panel, and look for any loose connection of the wires to the motor. Sometimes one of the electrical supply wires connected to the motor switch plate becomes dirty. Dirt creates resistance that creates heat which ultimately melts the wire, breaking the connection. Similarly, if the supply wire is undersized for the load, it will overheat and melt. Clean dirty switch plate terminals and reconnect the wiring.

Motor hums but will not start

The impeller may be jammed with debris. Turn off the breaker, and spin the shaft by hand. If it won't turn freely, open the pump and clear the obstruction. If it does spin, check the capacitor.

Check the capacitor for white residue or liquid discharge. Either is a symptom of a bad capacitor. To replace the capacitor, remove the cover that holds it on top of the motor. This cover is held in place with two screws. The two wires are attached to the capacitor with simple push-on and pull-off bayonet clips. Install a new capacitor.

The motor may hum and yet fail to run because of insufficient voltage. Use a multimeter to check the actual voltage and consult the utility company if there is a problem.

Loud noises or vibrations

This is most often caused by worn out bearings. Take the pump apart and remove the load (impeller and water), If the motor still runs loud or vibrates, it is the bearings. Take it to a motor shop, or better still, replace the motor, unless the motor is relatively new or is still under warranty. This problem can also be caused by a bent shaft, although that is not common.

The breaker trips

Disconnect the motor and reset the breaker. Turn the motor switch or time clock on switch, back on and if it trips again, the problem is either a bad breaker or, more likely, bad wiring between the breaker and motor. Be very careful with this test. Switching the power back on with no appliance connected means you are now dealing with bare, live wires. Be sure no one is touching them and that they are not touching the water, each other, or anything else.

If the breaker does not trip when conducting this little experiment, the motor is bad. This usually means there is a dead short in the windings and the motor needs to be replaced. Water can cause this.

Priming The Pump

Priming is starting the suction that gets water moving through the pump thus creating circulation in the pool. Most of the modern pumps are self priming, but when the water get drained from the pump it sometimes needs to be reprimed before it can get started.

Basic priming

Let's go through the steps to prime the pump in most of the pool and spas:

  1. Check the water level in the pool. Water is sometimes lost during maintenance and there might not be enough in the pool to fill the skimmer. Or some times the pump will not prime unless filled to the very top of the skimmer.
  2. Check the water path. Many a times, priming problems are not related to the pump, but to some obstruction. Check the main drain and the skimmer throat for leaves, debris, or other obstructions. With the pump turned off, open the strainer pot lid and remove the basket and dispose off the leaves and debris. Last, make sure that once the pump is primed be sure all valves are open and that there are no other restrictions in the plumbing or equipment of the pump.
  3. Fill the pump. Always fill the strainer pot with water and replace the lid tightly so air cannot leak in. Keep adding water until the pot overflows so you fill the pipe as well as the pot. Sometimes the pump is installed above the pool water level so you will never fill the pipe unless a check valve is in the line as well. Quickly, just fill what you can and close the lid.
  4. Start the motor and open the air relief valve on top of the filter. The pump is primed if all the air is replaced with water and the normal circulation begins. It is advisable to wait for couple of minutes for the pump to prime itself, but at the same time make sure that you do not overheat by running a dry pump.

Sometimes repeating this procedure two or three times will get the prime going. If there is a check valve in a long run of pipe, each successive filling of the pot pulls more and more water from the pool, which is held there each time by the check valve. Also, if it is warm outside, the air in the pipe might expand and create an airlock. The repeated procedures might finally dislodge the air.

The blow bag method

When basic priming fails, try a drain flush bag, also called a blow bag. The drain flush is a canvas or rubber tube that screws onto the end of your garden hose. Slip this into the skimmer hole that feeds the pump and turn on the hose.

The water pressure makes the bag expand and seal the skimmer hole so the water from the hose cannot escape and must feed the pump. After running the hose a minute or two, turn on the pump. When air and water are visible returning to the pool, pull the drain flush bag out quickly, while the pump is running, so pool water will promptly replace the hose water.

This method is not effective if the skimmer has only one hole in the bottom, for this hole is connected not only to the pump but also the main drain. The forced water from your drain flush bag will take the line of least resistance and flood through the main drain rather than up to the pump. In the two hole skimmer, the hole furthest from the pool usually is plumbed directly to the pump. Your drain flush bag in this hole will give good results.

Filter filling method

Another method is filter filling. Open the strainer pot, turn on the motor, and feed the pot with a garden hose. Open the filter air relief valve and keep this going until the filter can is full (water will spit out of the air relief valve). Close the air relief valve, turn off the motor and garden hose, and quickly close the strainer pot. Open the air relief valve. The filter water will flood back into the pump and the pipe that feeds the pump from the pool. When you think these are full of water, turn the motor back on. The pump should now prime.

Detecting air leaks

When none of the above mentioned methods work, then there is the problem of air leaks. The problem might be that the pump is sucking air from somewhere. Air leaks are usually in strainer pot lid O-rings, or the pot or lid itself has small cracks. The gasket between the pot and the volute might be dried out and leaking. Of course, plumbing leading into the pump might be cracked and leaking air.

If any of these components leak air in, they will also leak water out. When the area around the pump is dry, carefully fill the strainer pot with water and look for leaks out of the pot, volute, fittings, and pipes. Another way is to fill and close the pot, then listen for the sizzling sound of air being sucked in through a crack as the water drains back to the pool.

Sometimes there's just no easy answer. This time remove the pump and carefully inspect all the components, replace the gaskets and O-rings, and try again.


Many pumps employ threaded T-shaped bolts that secure the lid to the strainer pot. Sometimes these corrode and snap off, with part of the bolt remaining in the pot. If part of the broken bolt extends above or below the female part on the pot, try using pliers, especially Vise-Grips, to grasp the broken section and twist it out, like removing a screw. Replace with a new T-bolt.

If this doesn't work, take your tap and die set or electric drill and tap a small hole inside the broken piece, then use your Phillips-head screwdriver to grip inside the hole and twist out the broken piece. If all else fails, remove the pot from the pump and take it to a machine shop to be tapped out and rethreaded.

Reverse Flow Problems

Reverse flow problem occurs with many pumps. But it has been observed that reverse flow problems does not occur with semi-open face impellers. When the pump is pushing the water, the air may get trapped in the filter due to either the leak in the system or due to improper blending of the filter with the new installation. While the running pump is pushing water against the trapped air bubble in the filter, the power to the pump motor is interrupted. The moment the power goes off the pump stops, releasing the bubble of air. This instant release of air forces the column of water between the pump and filter to reverse and flow backwards toward the pump, entering the discharge side of the filter. This reverse flow of water into the discharge side of the pump starts the impeller turning in the wrong direction. Within a few short seconds the pump impeller can be turning at high speeds driving the motor in reverse as well.

When power is restored and the motor does start while turning in the wrong direction, the torque of the motor can be great enough to loosen and spin the impeller from the shaft, stripping the threads.

Reverse flow is a very rare occurrence and as far as we can determine it can be overcome simply by using a check valve between the filter and pump. This is the most effective way to prevent it. Several large pump manufacturers have recognized the same occurrence and to prevent reverse flow have been securing the impeller to the motor shaft. This, of course, prevents the impeller from stripping its threads.

Model And Makes

A look at the manufacturer's literature or catalogs at your local supply house will reveal that all pumps are variations on two basic concepts.

Motors to drive these pumps are made by several manufacturers as well, although I know of none who make both pumps and motors. Century, Franklin, A.O. Smith, General Electric, and others make all the various styles and horsepower of motors needed to run modern and older pump equipment. Some of the styles you will encounter and need to specify when replacing are as follows. Remember, the nameplate on the motor gives you this information, but it is often obscured or missing, so be familiar with these types.

C Frame

If you look at the face of the motor, the end with the shaft, you will note a definite pattern in the casting that looks like the letter C. The shaft is threaded, meaning it has male threads on the end of the shaft to receive the female threads of the impeller; or keyed, meaning the shaft has no threads, but rather a channel that runs the length of the shaft to accept the setscrews.

Square Flange

Look at the end of the motor that has the shaft. This style of motor includes a flared bracket, square of course, that accepts the seal plate of the Sta-Rite pump and the corresponding motor. These are only made with threaded shafts because they work only with the type of pump that uses a threaded impeller.


These are not in use much anymore. The uniseal motor includes a flange like the square flange for application with a uniseal-type pump.

48 Frame

This is the motor used on indoor spa booster pumps and fits that particular style. Jacuzzi makes a number of pumps that use the 48 frame. These are all threaded shafts.

Motor Characteristics

Now let us examine some of the different characteristics of the motors.

End Bell

The housing at each end of the motor is called the end bell. It is made of aluminum or cast iron, the latter being more expensive. Iron rusts and aluminum doesn't and aluminum more efficiently disperses heat away from the motor, thereby prolonging its life. Some manufacturers give you a choice within each type of motor.

Full-Rated Or Up-Rated

The full-rated motor operates to its listed capacity (1 hp, 2 hp, etc.). The up-rated motor has a similar horsepower rating but functions to even higher standards if called upon (see the section on service factor). This might be useful if the pool or spa gets full of leaves, for example, and the motor is required to work against increasing loads until someone clears out the debris. By checking the service factors, you might be able to get a 1/2-hp up-rated motor that is able to perform as well as a 1-hp full-rated motor.


As the name implies, this motor includes a switch box to wire it for two-speed operation. Spas, for example, often use a two-speed motor with the lower speed for circulating and heating, and the high speed for jet action. Wiring instructions are printed on the motor as described previously.

Energy Efficient

As described previously in the section on motors, the so-called energy efficient motor is, in fact, a design that saves electricity over a comparable motor of standard design. The special characteristics of pumps and motors for automatic cleaner boosters are discussed in the section on automatic cleaners.

Motor Covers

Protective covers are made to fit over motors and are designed to keep direct sunlight and rain off the motor housing. They are made from either plastic, metal, or foam rubber. In fact, the motor is designed to do this itself. You will notice that the motors in the illustrations all have air vents on the underside. The greatest danger to a motor is flooding of the equipment area in heavy rain or when opening a filter, or allowing water from the ground to get up into the motor. This will short out the windings and void any warranty.

Submersible Pumps And Motors

There are essentially two types of submersible pump and motor combinations that you will encounter.

High-Volume Pump-Out Units

Sometimes you need to drain a pool or spa. Several manufacturers make pump and motor units with long, waterproof electrical cords, that can be completely submerged. The suction side is at the bottom of the pump, as if a regular pump and motor unit were stood on end with the motor on top and the pump on the bottom. The return line is sized to be attached to your vacuum hose. Smaller units are connected to a garden hose to feed water out of the pump.

Low-Volume Pumps And Motors

Fountains and small ponds use small submersible pump and motor units that contain all of the same components as the larger ones, except that their size is small. These have waterproof electrical cords so they can be submerged in the body of water.

Both high- and low-volume types contain the same components as the pumps and motors described earlier and are repaired in much the same ways. Submersibles have more crucial and tricky seals and gaskets, however, because leaks in these mean electricity in the body of water that can be fatal to both the motor and you. Any repair of the pumps should be done by certified electrician.

Cost Of Operation

As with any electrical appliance, you can easily calculate the cost of operation. Electricity is sold by the kilowatt-hour. This is, 1000 watts of energy each hour. You know that volts x amps = watts, so you can look at the motor nameplate and see that the motor runs, for example, at 15 amps when supplied with 110-volt service, and 7 amps when supplied by 220-volt service.

Let's say the pump in our example is running on 220-volt service-220 volts x 7 amps = 1540 watts. Looking at an electric bill, you learn that you pay 15 cents per kilowatt-hour. As noted, a kilowatt is 1000 watts, so if you divide 1540 watts by 1000, you get 1.54. That is multiplied by your kilowatt rate (15 cents), equaling 23 cents for every hour you run the appliance. If you run the motor eight hours per day, that means 23 cents x 8 hours = $1.84/day. Over a month, that equals 30 x $1.84 $55.20/month.

Booster Pumps And Motors For Spas

Pump and motor units that provide only jet action for spas generally are not equipped with a strainer pot and basket, otherwise they are the same as other units, that are used for the pools. Some units are designed to perform two functions and therefore run at two speeds. They run at high speed (3450 rpm) to provide jet action. But at a low speed (1750 rpm), they also circulate, filter, and heat the water and would have a strainer pot and basket.

To operate efficiently, spa jets require 15 gpm running through each one. Therefore, if you have a system that delivers 60 gpm, you can install up to four jets. Also, each jet requires 1/4-hp from its pump and motor, thus four-jet spa would need at least a 1-hp unit.

Remember, this assumes the pump is doing no other work. If it is pushing water through the filter and heater before getting back to the jets, or if the equipment is more than 20 feet from the spa, then some power will be lost and you will need to calculate more than 1/4-hp per jet.

When planning a system or replacing equipment, many codes require that a spa to turn over completely two times per hour, so be sure the pump can handle that, especially when the filter gets dirty and head increases.