How A Pool Pump Works


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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.

Click here to view pool the Hayward Super 2 pumps. 

Things You'll Need


Step by Step


Step 1

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

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

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).

Click here to view the Hayward Super 2 pump parts. 

Step 4

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

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

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.

Click here to view pool pumps. 

Step 8

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

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

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.

Click here to view GOKITS. 


(1 to 40 of 121)

 Posted: 2/10/2020 

I have a Hayward SP3210C impeller and a shaft seal PS-3890 how is the seal installed all DIY show the seal put on the impeller but there is now way it would fit on this impeller is thes the correct shaft seal if so how is it installed

InyoPools Product Specialist  Posted: 2/12/2020 

If you are having trouble getting the shaft seal to fit over the stem of the impeller, you probably have a piece of the old shaft seal that still on the stem. This is a common thing that pops up because the shaft seal cuff looks like it is part of the impeller. For an example, look at step 16 of this guide: How To Replace a Pool Motor Shaft Seal

 Posted: 1/13/2020 

Does the impeller tend to tighten in the pump after the pump is running? Or does it loosen? I’ve noticed some pumps have a bolt to hold the diffuser in.

InyoPools Product Specialist  Posted: 1/13/2020 

The motor shaft spins in the direction that would tighten the motor rather than loosen. This is why it is such a task to get an impeller off the motor shaft after it has been installed for a while. Regarding the diffuser, it is pump dependant; some are secured by a couple of screws or notches and nubs in the seal plate. On old pumps, impellers would have lock screws that held them on the motor shaft. Lock screws are no obsolete, as most motors are made with threaded shafts instead of keyed shafts.

 Posted: 7/2/2019 

I have a challenger pool pump that the diffuser is bolted on with the left thread bolt and everytime I tighten it and then put it back together turn on the motor the boat loosens and vibrates out of place causing no pumping action

InyoPools Product Specialist  Posted: 7/2/2019 

It seems like the threads molded into the seal plate are either loose. There is not much recourse otehr than to replace the seal plate: Seal, Plate (355004, Black) - 355303

InyoPools Product Specialist  Posted: 7/1/2016 

SooseaQ - Sounds like the motor is overheating. Does the motor shut off in the Rinse position too? If so, something may be blocking the Waste port. Check your Waste line. Also, check the spider gasket in your multiport valve to make sue it is not damaged. See our guide on "How to Replace a Spider Gasket on a Multiport Valve".

 Posted: 6/30/2016 

I have a 1 HP sand filter with multi-port valve which works fine in the filter position. As soon as I try to backwash, it runs for about 5-10 seconds then the motor shuts off. It will turn back on after about 10 min. I realize that it is the safety on the motor but what is causing the shutoff when I place the valve in Backwash position? The water seems to be flowing fine and I don't have any visible leaks.

InyoPools Product Specialist  Posted: 4/22/2016 

Bama - The seal plate and shaft seal are on the discharge side of the pump so if there is a leak there you would have water squirting out not air sucking in. Recheck all your seals before the impeller for air leaks. Also check the motor drain plug on the suction side.

 Posted: 4/20/2016 

I have a Hayward Super II Pump system, 3 HP on a 11+ year old pool. I have replaced the impeller shaft seal and all gaskets 3-4 times with no problem until recently. I replaced all gaskets and seals last week and restarted pump. Still had a little leaking water so I thought it was probably the seal plate because it was really rough when I replace the seal this time. Pulled apart and cleaned everything including the seal plate (ordered new seal plate to go ahead and replace), reassembled and now I can not get pump to prime. Any ideas? Could the seal plate/shaft seal allow on the backside of the impeller allow air into diffuser/impeller chamber on the pressure side?

InyoPools Product Specialist  Posted: 8/25/2015 

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.

 Posted: 8/22/2015 

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.

 Posted: 3/20/2015 

Thank you for your advice. Very helpful.

InyoPools Product Specialist  Posted: 3/20/2015 

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.

 Posted: 3/19/2015 

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?



InyoPools Product Specialist  Posted: 3/19/2015 

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.

 Posted: 3/18/2015 

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?



 Posted: 3/18/2015 

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??



InyoPools Product Specialist  Posted: 1/15/2015 

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.

 Posted: 1/14/2015 

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

InyoPools Product Specialist  Posted: 10/12/2014 

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.

 Posted: 10/11/2014 

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?

InyoPools Product Specialist  Posted: 6/3/2014 

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.

 Posted: 6/2/2014 

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.

InyoPools Product Specialist  Posted: 5/20/2014 

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.

 Posted: 5/19/2014 

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?

InyoPools Product Specialist  Posted: 2/26/2014 

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.

 Posted: 2/22/2014 

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?

InyoPools Product Specialist  Posted: 7/28/2013 

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.

 Posted: 7/25/2013 

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?


InyoPools Product Specialist  Posted: 7/23/2013 

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.

 Posted: 7/22/2013 

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.

InyoPools Product Specialist  Posted: 7/16/2013 

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.

 Posted: 7/14/2013 

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 ??

InyoPools Product Specialist  Posted: 6/23/2013 

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"

Anonymous  Posted: 6/21/2013 

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?

InyoPools Product Specialist  Posted: 6/11/2013 

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.

Anonymous  Posted: 6/10/2013 

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

InyoPools Product Specialist  Posted: 4/23/2013 

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.

 Posted: 4/22/2013 

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!