How A Pool Pump Works

Written by:  Danny Rhodehamel

This page provides a short tutorial on the main parts of a pool pump and how a pool pump works. This example describes a Hayward Super II Pump but the pool pump's parts and it's operation are common to most pool pumps.

Tips & Warnings


Things You'll Need

Step by Step

Step 1
how a pool pump works

This picture shows the main parts of the pool pump in a pump cut-away. These parts include: the strainer basket cover that provides access to the strainer box to add water and clean out debris; the strainer basket that filters the larger pieces of the debris; the diffuser that direct water to and collects water from the impeller; the impeller that generates water pressure through centrifuge; and the motor that drives the impeller. Also shown are the two ports where water enters into the pool pump from the pool and exits out or the pump to return to the pool.

Step 2
pool pumps

This picture shows the basic flow of water through the pool pump. Water is sucked in through the basket, through the center of the diffuser (yellow) and through the center of the impeller. As the impeller spins, the water is thrown out the outer slots of the impeller where it is collected by the diffuser. The water is then funneled though slots in the diffuser into the high pressure water chamber and then out the exit port to the pool. Two notes: this picture shows a cut-away of the pool pump so that you can see the internal parts of the pump. In a working pump the diffuser would completely enclose the impeller. Also the only moving part in this pool pump is the impeller driven by the motor shaft. It's centrifugal motion is what sucks the water in and pushes the water out under pressure.

Step 3
how a pool pump works

This picture shows the inner operation of the diffuser with the diffuser partially pulled off. The diffuser funnels water from the strainer pot into the center of the impeller, then collects spun water from the outside edges of the impeller and releases the water through its own slots into the pressured chamber (dark blue arrows).

Step 4
pool pump impeller

This picture shows the operation of the impeller. Water enters the center of the impeller. As the impeller is spun by the motor, a series of blades, like a fan, push the water to the outside edges of the impeller where it exits through slots to be collected by the diffuser. It is this centrifugal force that generates the high pressure of the water exiting the pool pump.

Step 5
pool pump chambers

The pool pump has two chambers: chamber 1, the strainer pot, in the pull side of the pool pump before the impeller; chamber 2 is the push side of the pump after the impeller. There are four seals that keep the water flowing correctly between the chambers.

Step 6
how a pool pump works

This cut away of the pool pump shows the 4 seals that are part of most pool pumps: the strainer pot gasket, the diffuser gasket, the housing gasket, and the motor shaft seal. Their deterioration is the source of many of the common pool pump problems that plague pool owners.

Step 7

The strainer gasket usually sets in a groove on top of the strainer pot and provides a seal for the strainer pot cover. A poor strainer gasket will allow air to be sucked into the pump and prevent priming. The instructions for replacing a pump lid O-ring are included in the following guide: How To Clean Out the Pump Strainer.

Step 8
pool pump diffuser gasket

The diffuser gasket provides a seal between the strainer pot and the chamber around the diffuser and impeller. This chamber collects the pressurized water that is released through the output port. Without this seal the pressurized water will blow back into the strainer pot and the pool pump will loose pressure. For instructions in how to replace a diffuser gasket go to How To Replace Pool Pump Gaskets.

Step 9
how a pool pump works

The housing gasket provides the seal between the motor assembly and the pool pump assembly. If this seal is bad, the water will spray out of the pool pump and you will loose pressure and water. For instructions in how to replace a housing gasket go to How To Replace Pool Pump Gaskets.

Step 10

The motor shaft seal prevents water from leaking out of the pressure chamber along the motor shaft into the motor assembly. When this happens you will see water dripping from the bottom of the motor. For instructions in how to replace a motor shaft seal go to How To Replace A Motor Shaft Seal.

Step 11
how a pool pump works

If you are repairing your pump or pump motor consider purchasing a GO-KIT. Each GO-KIT contains the replacement seals and gaskets you will need to repair your pump. A typical GO-KIT like the one pictured here for a Hayward pump, contains the motor shaft seal (2 parts), the pump housing gasket, the pool pump lid o-ring and the diffuser gasket. Note: These GO-KIT are generally unique to the make and model of the pump. Order the GO-KIT specified for your pump's make and model.

Comments (1 to 40 of 111)

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User: Inyopools

Dean - To convert your motor from 230V to 115V, according to the Jacuzzi rep, the black box connected on the right side of the terminal strip, should be shifted over to the left so that the arrow on the box lines up with the 115 arrow on the terminal. See Steps 6-8 in our guide on "How To Wire A Pool Pump" for more detailed instructions.

User: Dean

I just purchased the 1 UMF-S 1 HP from you and replaced my old 1 UMF-S. However, the pump runs for about 5 mins then shuts off. It'll start back up a couple of mins later but continues to do this. From what I've read, my pump may be set at an incorrect voltage. How do I change this to the correct one. The instructions are ambiguous at best. I just transferred the wiring from my old one to the new one so I know it's installed correctly.

User: Ron

Thank you for your advice. Very helpful.

User: Inyopools

Ron - A 3/4 HP pump is not too big for your system especially if your pool system has worked previously. Did you change anything a month ago? Is so, I would concentrate on that area. Also I would think of this as a garden hose with a nozzle. High pressure would be caused by restricting the discharge side of the hose not the input side. Is there anything that is partially blocking the system after the pump? You mentioned gaskets. Leaking gaskets tin the suction side of the pump would reduce pressure. Leaking gaskets after the pump will show as sprays but would not increase pressure.

User: Ron

Thanks for your response. What is most strange is that the system worked just find until about a month ago, which is why I am so puzzled. The system is pretty basic, (in ground, liner pool. One skimmer with Mamba hooked to it, one return. Only adjustment at skimmer connection, wide open or closed makes no difference. 3/4 hp motor has been a workhorse for many years.

If the gaskets were screwed up, could that cause pressure to rise?


User: Inyopools

Ron - I assume you have changed the diverter valve settings to open up any lines that may be closed to spread out the water pressure across the whole system. If that is not the issue, it sounds like your pump is too large for your pool system. If so, you have two options. The least expensive is to replace the pump's impeller with one size smaller. You might have to change the diffuser also. The other option is to replace the motor with a smaller one.

User: Ron

Tried to post this earlier, not sure it took. Sorry if double posted...

I have a Hayward SP-3000d system. The problem I am having is WAY too much pressure, causing my suction pool cleaner (only moving part is flapper) to stop working because flapper is pinned to one side of the cleaner, due to really high pressure. Water from return is shooting out, nearly causing waves on the surface.

I have cleaned cartridges, tube inside cartridge holding tank, checked all the pipes, pulled apart the pump and motor, and replaced the flapper on the Mamba pool cleaner. All to no avail. Any idea what could be causing severe overpressure?


User: Ron

Nice presentation.
I am experiencing a problem with my Hayward SP-3000d pump/filter. This system is generating SO much pressure that my pool cleaner's flapper valve is pinned to it's housing. The amount of water coming through the return is nearly making waves on the pool surface, so a I don't think I have a clog. Replaced flapper on pool sweep, cleaned filter cartridge and small tube inside filter housing, checked all the pipes for clogs, etc. Cannot find any information as to what could be causing this incredible amount of pressure. Any ideas??


User: Inyopools

Betty roux - I don't see how leaking under the motor would be caused by an unlevel motor. Leaking under the motor is usually a sign that the shaft seal is leaking. When you had the motor and shaft seal replaced, did you replace the seal plate. Sometimes when the pump is run without water, the shaft seal gets really hot and melts the area around where one half of the seal is inserted, and that causes a leak. You may have to replace the seal plate of the pump.

User: Betty roux

We had problems priming the pond pump after cleaning debri out of basket, took to motor company close by. They replaced motor with 3/4 A Smith motor. Put back on, took awhile to prime, started leaking under motor, took back, said pump seals melted, not primed properly, all seals &'pump replaced, still leaked although primed, with only 1-11/2 minutes primping. Returned, seals replaced, still leaked. Company came out, saw motor cocked slightly down, also pipes out of wall gradually down also, his contention is this is causing leaking. Proped intake curve to basket up, maybe 1", said need pipes need reworking so motor lays flat to prevent leaking. It still leaks! My husband said it's always been that uneven level, it took long time to prime previously, but never leaked & pumps could be at any level if properly aligned, shouldn't leak!! Any suggestions would be appreciated

User: Inyopools

jrodelander - Could probably be one or two problems. Hopefully your motor's humming is due to a faulty capacitor. See our guide on "How To Replace a Pool Pump Capacitor" for more information. If it's not the capacitor, the windings in the motor may be damaged, which will mean buying a new motor.

User: jrodelander

we recently repaired the ceramic shaft seal on the pump motor. all good, no leaks, water being filtered. However, when I turn the motor off to backwash, etc, the motor hums before it catches and begins pumping again. Have you suggestions?

User: Inyopools

uitfan21 - Check the voltage coming into your pump. If your pump is set up for 220V, you should have 220V supply. Check that all connection to the pump are tight. If you are using an extension cord, make sure it is heavy enough to carry the current to the pump. Then I would contact the company you bought the pump from. You may have a bad pump.

User: utfan21

Our pool pump is 2 weeks old and now will not work as of today. It will not come on or make any noise when plugged up. Any ideas what could be wrong? I checked all the breakers and nothing is tripped. There is power going to the pump it will not come on.

User: Inyopools

trixie0318 - Sounds like you are getting air into the system and the pump is not fully primed. Is the strainer basket full of water? Do you have any other suction ports open? You should not run the motor on and off like this. It will damage the motor.

User: trixie0318

Due to a large amount of algae we decided to drain our pool and Start fresh this almost all of the water out of the pool and cut off motor..due to taking it was a couple of days later before we couple finish cleaning before we refill pool. There is about 6 in of water in my 24 ft round pool. We have vaccum hose hooked straight up to pump. Motor was working great then got hot started smoking and shut off...its on a safety switch. After few minutes pump will come back on after switch is reset but repeats. Housing is not staying full even with end of hose submerged. Is this due to water level or motor problems?

User: Inyopools

trav - Please click here for the Jacuzzi Magnum parts list. The picture shows two drain plugs at the bottom of the pump labeled "7". If this is where your pump is draining, these plugs need to be re-installed. They also have o-rings labeled "6" that are required behind the plugs. Make sure they are there. If the plugs and o-rings are in place and the pump is still leaking at these points, you may have to replace the o-rings.

User: trav

I have a jacuzzi magnum 1umf-s that pumps to a sheer descent. Whenever I open the valve to the pump, water starts draining from two holes near the bottom of the pump. How do I stop this?

User: Inyopools

judy - It's hard to pinpoint your problem based on your comments. Here's a link to our guide on "How To Correct Low Water Pressure in Your Pool System". It identifies some of the situations that cause low water pressure.

User: judy

I am so frustrated with my pool. I sure that you can help me.
My pool is 14 yrs old. My problem is the power in my jets. Either they are low or just stops. I have replaced the motor, gaskets, rings, caps & top of filter basket. After spending about $1,000, I have the same problem. This problem is intermitant so it's hard to fine. Because it works on & off, I keep getting algee & spending more money on products. Any suggestions for my pool man?

User: Inyopools

poolsss - This is a gravity fed pump so make sure it is installed below the surface of the water. Also if this pump has run for a period of time without water, you may have damaged the shaft seal, and, if so, it may be spraying water over into the motor. This could short out the windings and at this point you might have to buy another motor.

User: poolsss

This is our second year with an above ground pool and last summer, the pump worked fine, but this year when we put in the pump it first was leaking. We eventually got the leaking to stop but now the water is not being pump, entering or exiting. However, the pool pump is on and we can hear it. Now our water is green and we haven't been able to use it all summer.

User: Inyopools

Danny Slaughter - Polygroup had this comment in their literature. "When the pump is first started, there may be air present in the chamber that may create a vacuum and prevent water from going through the pump. Slowly open the air valve to release the trapped air and for the pump to fill with water then close the air valve. Your pump should be working fine now." If this doesn’t help, your motor should be covered by their warranty.

User: Danny Slaughter

I vaccumed my pool out yesterday. Afterwards, I proceeded to do as I always do and took the filter and skimmer basket out to clean it out then replaced it. After I went inside for a while I came back out and my pump had stopped working and we can't get it to work. We haven't even had it a month yet so will the manufacturer warranty cover a new one for it?? Please help bc I can't afford to buy a new one! Or if anyone can tell me what might be wrong with it and what parts I would need to get it fixed! I tried calling the polygroup customer service number today but they were closed and I need this fixed ASAP ??

User: Inyopools

reconnecting pool - Here's a link to common pool configurations: Plumbing Schematics. Also look at our guides on "How To Set Up In Ground Pool Equipment" and "How To Open Your Swimming Pool"


We jst bought a new homeand want toopen the pool. All of the connections are disconnected. Do you have anything that can showus how to connect? how to turn on etc?

User: Inyopools

Noisy motor - Take the motor out of the pump housing and check the state of the impeller and diffuser. Sometimes they are clogged or damaged by debris and the parts start rubbing against each other. If the parts are good and you have an older motor, the motor bearings may be going and it's probably time to get another motor. If you need to replace the motor, look into buying an energy efficient (EE) one.


my 1 hp hayward in grond pump works ok but seems to be noisey is something going.

User: Inyopools

poolma - Sounds like your problem may be in your filter. The backwash setting bypasses the filter. If your system has a good flow through the backwash setting and poor flow in the filter setting, try backwashing your filter a couple of more times. It may be time to replace your filter sand or DE. Also check to make sure that your motor's impeller is not clogged. If clogged it might provide enough pressure to backwash but not to filter. See our guide on How To Clean out a Pool Pump Impeller.

User: poolma

How do I locate the problem.
The pump works fine to back wash the system but when I switch it back to run(circulate)them water in and out of the pool is minimal. The motor sounds like it's run fine but isn't moving the water through. The skimmer baskets won't even stay in place. What do I do first? The temperature is rising please help!

User: Inyopools

Pat - Intermittent pump operation can be caused by the wrong or unstable voltage to your pump's motor. If the motor is set up to run on 220V and it is wired for 115V, it will become over heated and temporarily shut down to cool. This will damage the motor over a short period. Use a volt meter to check the voltage into your pump's motor. Also check that the voltage to the motor is stable and does not decrease more than 15% up and down. If it is unstable, contact your power company.

User: Pat

My pump will shut off for 30 to 45 seconds and then come back on and run fine for 30 minutes or so then shut off again. Its been doing this since it was new. It does'nt seen to hurt anything, what may cause this.

User: InyoPools

Jim - I would pull the motor off of the pump and check that the impeller is still sound. If the impeller is good, check for leaks on the suction side of the pump. See our guide on locating leaks. Otherwise, like you say, you've done well to have this motor for 14 years. It may be time to replace it with a more efficient one.

User: Jim

My pump motor is operating, but it is not pumping the water. It doesn't make any unusual noise. What is the most likely cause. Could it be that the impeller is has broken loose from the motor shaft? Is it likely that I need a whole new pump. The motor pump assembly is fourteen years old.

User: InyoPools

Richard - Check for obvious leaks around the filter or any joints you separated to change the sand. Check to see if water is going out your waste line. If it is, you may have a blown spider gasket in the multiport valve.

User: Richard

after changing the sand in my filter whenever i have the pool on filter the pool is losing water as if the waste outlet may be open? please help

User: InyoPools

Dennis - Take the motor out of the pump and see if you can spin the shaft easily. If not , you may need a new motor. Also check that the impeller is not jammed. Then check your motor's capacitor. It may have failed.

User: InyoPools

Francis - If you have a cartridge filter, you can bleed the air out by opening up the relief valve at the top until only water comes out. However I doubt that is your problem after running two hours. Sounds like you have an air leak. Check anything that was changed during the pool cleaning like the strainer basket. Is the cover gasket on correctly?

User: Dennis

Pump motor is not running at all. I have power from the breaker box, the breakers have been checked,they're fine the timer is fine and the time clock is fine have power to the pump but motor is not running Bad pump?

User: Francis

My weekly pool cleaners came this am, turned on the filter, cleaned the pool and then they shut the filter down. My pool filter starts at 10am, now two hours later the jets are spitting out air bubbles and water. The motor window has air in it. Question, how do I get the air out?

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