Troubleshooters.Com and Steve Litt's Pool Ressurection Page Present

Anatomy of a Pool Pump

Copyright (C) 2006 by Steve Litt





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I'm Steve Litt. I created the Universal Troubleshooting Process (UTP). I create and license UTP courseware, as well as teaching the UTP onsite. I've written four books on troubleshooting: Twenty Eight Tales of Troubleshooting, Troubleshooting: Tools, Tips and Techniques, Troubleshooting Techniques of the Successful Technologist, and The Manager's Guide to Technical Troubleshooting. Past professions include software development, electronic repair and corrosion protection.

I've never been a pool professional. I've had a pool only 5 years, and until autumn of 2004 it was maintained by a pool professional. So what gives me the authority to write this web page? A few weeks ago my filter pressure could not go above 5 PSI, even when the pool appeared to partially prime. I looked for obvious vacuum side leaks, and finding none, followed a friend's advice and checked out the pump's impeller. Here's what happened...      
How did I figure this out?

I'm frequently asked "Steve, how do you know so much about so many things?"

The skills attained from following the Universal
 Troubleshooting Process help me fix almost anything.


The impeller is attached to the pump's shaft, so once you remove the motor from the pump assembly, and then remove the diffuser (pictures shown later in this document) from the motor, you have direct access to the impeller. But life is never that easy...

Generation upon generation of professional and amateur pool repair personnel had made the pool's piping into a patchwork of fittings. The last guy who worked on the system repaired a leak in the drain/skimmer valve, but to do that he had to mount the pump such that the pump motor was 3/4 inch from the house, as shown in the following photo:
Pump mounted too close to house Notice the quarter wedged between the pump and the house. If you click the image to enlarge it, you can see George Washington on the quarter.

This is much too close to pull the pump motor out of the pump assembly, and as you can see, the pump assembly is solidly piped in place. I needed to totally repipe, but that's another subject for another web page.

So I repiped using all flexible 1.5" piping on the intake side of the pump, and mostly solid 1.5" PVC with a straight stub of flexible on the outflow side. Combined with unions at the intake and outflow holes, this bestowed the ability to quickly connect and disconnect the pump from piping, and to compensate for small errors in pipe lengths or angles.

While I was at it, I disassembled the motor. What I found was that the pump's impeller was clogged and totally jammed with debris and berries. I brought the motor to Pinch A Penny Pool in Apopka, Florida. They had an extremely knowledgeable person who replaced the impeller, as well as the shaft bushings, which had worn out. I also had him install a new gasket on the diffuser.

This web page details the disassembly of a pump motor. I disconnected the pump from both the intake and outflow pipes, as well as the electrical hookup, so that I could disassemble it on a table and take pictures.

Basic Dissassembly

Here's what the pump looked like:

Pump with piping stubs As you can see, the pump assembly is sitting on the table. To show piping connections, I screwed pipe stubs into the intake hole (front of the pump) and the outflow hole (top of the pump). The big boxy thing in front is the pump basket. The cylindrical thing in back is the pump motor. The J shaped "pipe" going into the motor near the back is the electrical fitting.

As you'll see in later pictures, the intake and outflow holes are simply internally threaded holes into which you can screw a male threaded 1.5 inch PVC pipe. (Modern pumps often use 2 inch PVC).

You can click on this image to see a full size image.

The first thing I'll show you is the back of the pump assembly (back of motor):
Back of pump assembly In this picture you get a great view of the electrical fitting, as well as the two screws (at about 1 oclock and 7 oclock) that hold the cover on the back of the pump motor. Looking beyond the back of the motor, you see four hex head bolts, 9/16", that hold the pump to the pump basket. These bolts are at about 1:30 oclock, 4:30, 7:30 and 10:30.

You can click on this image to see a full size image.

Assuming you'll be unhooking or rehooking the electrical, or if you'll be replacing the impeller, you must first remove the pump's back cover:
Removing the pump motor's back plate Here you see me removing the screws that hold on the pump motor's back cover. Note that these screws also have hex heads (1/4" as I remember), so if you don't have room for a screwdriver, you can use a socket wrench.

You can click on this image to see a full size image.

The following is what it looks like after the back cover has been removed. If you're interested in electrical connections, you'll probably want to click on the picture to enlarge it.
Pump motor with back removed See the two silver screws just inside from the J shaped electrical fitting? Those are for the two hot electrical wires. Most pool motors run on 240 volts, so both wires are hot, not hot and neutral. As far as I know, even if you run on 120, which silver screw goes to hot and which to neutral is a matter of indifference.

What IS important is the third wire -- the ground. The ground must be connected to the green screw at 1 oclock near the outside of the motor housing.

Your pump must be set up to run on either 240 or 120 volts, depending on your current pool electrical wiring. Setting the voltage is beyond the scope of this document. Have your pool store or pool professional set the voltage.

One more thing. In order to remove the impeller from the front of the motor shaft, you must hold fast to the back of the shaft. You do that with a box end wrench, which you fish through the wires just above the black capacitor on the left in this picture. The hex you grab is in the center of the motor assembly. It is obscured by the spring loaded contact in the center in this picture. It is NOT necessary to disassemble the spring loaded contact.

You can click on this image to see a full size image.

Now that the motor's back cover removal is described, the next step is to separate the motor from the basket assembly. You do that by removing the four 9/16" hex bolts visible in the picture below:

Back of pump assembly The four hex head bolts are clearly visible at 1:30 oclock, 4:30, 7:30 and 10:30. They unscrew counter-clockwise, like most other bolts. You can unscrew them with a socket wrench or box wrench.

You can click on this image to see a full size image.

Removing the pump motor Here you see me using a ratchet wrench with a 9/16" socket to remove one of the bolts. Once all four bolts are removed, the motor can be removed.

You can click on this image to see a full size image.

The pump motor has been removed Here the four bolts have been removed and the motor (left part in image) has been separated from the basket assembly (right part in image). Note that the basket assembly includes a cradle on which most of the motor rests when fully assembled.

On the full size image available by clicking this image, you can clearly see the ruler that shows that you must pull the motor back a full five inches before it fully clears the basket assembly. You can remove the motor with less back clearance (about 3 inches) by separating the diffuser from the pump assembly before fully removing the pump. That's not too difficult, but re-assembling with the diffuser inside the basket assembly is murder. I know because I once saw a pool professional do it, and he was cussin and fussin the whole time, and he got it wrong the first time and there was a leak, and he needed to take another 45 minutes to redo it.

Bottom line -- try to have at least 5 inches clearance behind your pump motor. Better yet, have the pump motor parallel to the house and pointed away from the filter so there's plenty of room. If you must remove and reinstall the motor with less than 5 inches of clearance, be prepared for several hours of trial and error during reinstallation. This is why I repiped with flexible piping complete with disconnect unions. I can have my way with this pump.

You can click on this image to see a full size image.

The Pump Basket

Now that the motor and basket are separated, let's take a quick look at the basket:
Back of basket assembly This is the back of the basket assembly. Looking straight down the center, you see the blue mesh of the basket screen. At the bottom you see the cradle that supports the motor after the motor is fastened to the basket assembly. You see the empty threaded screw holes at 1:30, 4:30, 7:30 and 10:30.

What you might not see unless viewing a full size image (available by clicking the image), you'll see a gasket running around the outer diameter. It fits into a slot around the edge of the back of the basket assembly. If it comes out during insertion of the pump assembly, you'll get a prodigious spraying leak out the pump. If you look carefully at the full sized image, you'll see that in this picture the gasket has come out of its slot at about 4:30 oclock. Be VERY careful to get this in right and lubricate it.

This gasket is one reason why you might want to separate the pump from the electrical supply, and do this work on a table where the work is easier.

You can click on this image to see a full size image.

Side view of the pump basket Here's a side view of the pump basket assembly. You get a great view of the cradle, and also of the outflow hole at the top. In the full sized image you can clearly see the threads inside the outflow hole.

You can click on this image to see a full size image.

Front view of the basket assembly Here you see the front of the pump basket. This is probably the most common view of a pump from the pool user viewpoint. Look through the threaded intake hole and you see the blue basket screen.

You can click on this image to see a full size image.

Notice the warning sticker below the intake hole. This is discussed in detail later.

Removal of the pump basket screen Here you see the lid removed from the basket, and the blue basket screen removed.

You can click on this image to see a full size image.

The pump basket screen is full of debris Here you see the pump basket screen, removed from the pump basket. There are leaves and other debris at the bottom. Clean often.

You can click on this image to see a full size image.

Front of pump basket, with screen removed Here's the pump basket with the screen removed. On top you can see the threaded outflow hole. In front you see the threaded intake hole, and looking through it, you can see the hole for the pump motor's impeller.

Looking carefully, you can see a gasket in a slot around the basket's top hole. The gasket is H shaped, and the holes should face up and down, not sideways. A leak through this gasket causes air in the system, and if bad, failure to prime. Clean and reseat gasket, removing debris, and then place pool and spa lubricant on the gasket before bolting down the top. If that doesn't work, replace the gasket. This gasket is one of the usual suspects when a pump doesn't prime correctly.

You can click on this image to see a full size image.

See the warning label? Read it and take it VERY seriously. It's reproduced in the next section.

Suction Danger

Suction danger label

Read the suction danger label above, and if necessary click the above label image for a full sized image. This is VERY, VERY true. There have been several cases of people sitting on a drain and getting their intestines sucked out. In one case I saw on TV, this happened to a young boy. He wasn't killed, but he must live the rest of his life with a colostomy bag.

As the label says, never use this pump for a spa or shallow pool with a bottom drain unless the pump is connected to another suction outlet so if somebody sits on the bottom drain, water is sucked from the other suction outlet.

Caution your children and friends NEVER to remove the drain cover. Yes, I know it's fun to dive and remove it to show you've removed it, but the next person might get stuck on the drain and drown, or lose his intestines. For the same reason, tell children and friends never to sit on a drain -- any drain. You never know when a pool toy might stop up the other "functioning suction outlet". Caution everyone with long hair not to get near any drain (or skimmer for that matter). I heard a story about a long haired young girl whose hair got sucked into a spa drain, and she drowned before anyone had the presence of mind to shut off the pool pump.

For similar reasons, NEVER completely turn off either the skimmer or drain in normal operation. Leave each open at least 20%. For maintenance you may need to turn off one or the other, but of course you'll be careful.

The forces on a bottom drain are incredible. Assuming a 1 foot diameter drain, you have 1/4*pi*D2 surface area, or 0.79 square feet. Calculating the volume of the water in the cylinder above that drain in an 8 foot pool, you have 8 x 0.79 or 6.28 cubic feet. Water weighs 62 pounds per cubic foot, so the water pressure alone is 62*6.28, or 390 pounds.

But that just scratches the surface. The air pressure above the pool must be added, and that pressure is 14.7 pounds per square inch, or 144*14.7 pounds per square foot. That's 2116.8 pounds per square foot, and as you remember the drain is 0.79 square feet, so the force from air pressure on that drain area is 1672 pounds. That pressure would exist even if the water were incredibly shallow or absent. Add those two, and the unfortunate person stuck on the drain is stuck there with a force of 1672+390=2062 pounds. Of course, the pump can't create a perfect vacuum, but even if it creates only half the atmospheric pressure in vacuum, that's still over 1000 pounds. Maybe a world champion weightlifter could escape, but not the rest of us.

Personally, I try to make it a habit to turn off the pump whenever my family swims in the pool. I just feel better that way.

If you ever see anyone stuck to a drain, run and turn off the pump instantly.

The Pump Motor

Now we've covered the pump basket assembly and safety, it's time to cover the motor.
Removing the diffuser Once you've removed the motor, the diffuser can be easily pulled off by hand. In the picture on the left, the diffuser is the piece on the right, and the rest of the pump motor assembly is on the left. If you look carefully on the full sized image (click the image on the left to see it full sized), you'll see a rubber gasket going around the outside of the narrow end of the diffuser. That gasket is what seals the connection between the diffuser and the pump basket assembly. If that gasket is missing, bad, or mis-installed, you'll have problems -- most likely a lack of pressure, because pushed water short-circuits right back into the supplied water. It's very much like having a hole between the ventricles of your heart.

The purpose of the diffuser is to route water into the front of the impeller, and then when water gets thrown out the diameter of the impeller, to route that water outside the diffuser so it can be pushed out the outflow hole.

You can click on this image to see a full size image. Also, the next picture will be clipped and annotated...

Annotated image of pump motor parts

You can click the preceding image to get a full sized version. As mentioned, the gasket outside the small part of the diffuser prevents incoming and outgoing water from mixing. The incoming water comes in the center of the diffuser and into the center of the impeller. The swiftly rotating impeller flings pressurized water to the outside, where it's directed by the channels at the edge of the diffuser into the outlet part of the basket, and then out the outflow pipe.

Front of motor with diffuser still attached Here's a picture of the motor with the diffuser attached. Notice in the full sized version of the picture that the diffuser is marked with the legend "Top" where the top should go, in order to make reassembly easy. The one fin on the outside is strategically placed for maximum output to the outflow pipe.

You can click on this image to see a full size image.

Motor with diffuser removed to show front of impeller Here's the front of the motor with the diffuser completely removed. Note the spiral vains inside the impeller. These vains help throw water, at high pressure, to the outside.

You can click on this image to see a full size image. Note also that the next picture is a closeup of this one.

Closeup of front of impeller Here's a closeup of the front of the impeller. From here you can clearly see the spiral vains, but you can also see the motor shaft right in the center. This shaft has screw threads with which the impeller attaches. As described earlier, to detach the impeller you need to grab a hex, at the back of the motor, in order to hold the shaft still, after which you turn the impeller to unscrew it.

If the spiral vains are clogged with debris, the pump will not maintain flow, in which the symptom will be low pressure at the filter and possibly failure to prime. In this case, lack of pressure would cause failure to prime, instead of the reverse, which is caused by a supply side leak.

You can click on this image to see a full size image.

Top view of pump and impeller Here's a top view of the impeller. Note the rectangular slits through which water is thrown after being directed by the spiral vains. If these vertical slits are cloggedwith debris, the pump will not maintain flow, in which the symptom will be low pressure at the filter and possibly failure to prime. In this case, lack of pressure would cause failure to prime, instead of the reverse, which is caused by a supply side leak.

You can click on this image to see a full size image.

Pump shaft bushings You might wonder what you see after removing the impeller. You would see the pump shaft bushings, as shown in the drawing. The spring loaded bushing fits over the appendage at the back of the impeller, with the heavy rubber side toward the back. Further toward the pump along the shaft is the bushing with a white side -- white side toward the impeller. The seal between the white part of the inner bushing and the rubbery part of the outer bushing is what keeps water out of the pump itself. If significant amounts of water were to intrude on the pump itself, the pumps bearings would quickly fail.

You can click on this image to see a full size image.

Back of an impeller Here's what the back of an impeller looks like.

You can click on this image to see a full size image.

Clogged impeller, front view Here's the front of my bad impeller. You can see some debris clogging the vains. However, before this picture was taken, I had already removed a voluminous tangled mess of debris. THIS was the cause of my low pressure symptom.

You can click on this image to see a full size image.

Side view of clogged impeller Here's a side view of my clogged impeller. See the collection of berries and other debris in the rectangular openings? This prevents throwing of water, which decreases both flow and pressure. This is probably the most graphic picture of the clog that caused my underpressure at the filter.

You can click on this image to see a full size image.


After all I've seen, in my humble opinion reassembly is easiest if performed on a workbench, and then the reassembled unit is connected to electrical power. Yes, that makes the electrical connection much harder, but it makes reassembly MUCH easier.

To reassemble on a bench, make sure the basket assembly gasket is correctly inserted in its groove all the way around, and lubricated with gasket lube. Attache the diffuser to the motor assembly by pushing it lightly in place, with the diffuser's "top" marking lined up with the top of the motor. Be sure the small gasket is placed properly around the outside of the front of the diffuser.

Place the basket assembly on its front, and carefully and slowly lower the motor, diffuser end first, into the basket assembly, trying your best not to dislodge the basket assembly gasket. Once the motor is snugly in place, hand tighten the four bolts, while holding up the pump and motor assembly so gravity continues to press the motor assembly down into the basket assembly. After hand tightening the four bolts, use a wrench to screw them down so the heads touch the motor assembly plate. Then go around and tighten one at a time. Repeat as necessary until reasonably tight. I do not know the foot-pound specification on these bolts.

Once the motor and basket assemblies are snuggly and properly attached, it's time to connect it to the electric wiring. First, make absolutely sure to turn off the electricity to the pump. Flip the breaker, and then use a voltmeter for good measure.

Bring the pump to the electrical hookup, feed the three wires through the J shaped electrical fitting, and tighten them down to their proper screws.


Depending on your situation, you might find it easier to remove the fitting with the conduit, screw down the leads, and then  reconnect the fitting and conduit. This makes it easier to feed the wires in and maneuver them to the proper screws.

If your ground wire is not insulated, be sure to thoroughly wrap it in electricians tape to prevent accidental shorting if the pump is moved while energized (this could happen if the pump is piped with flexible pipe). Better yet, buy some green wire of the same gauge, push it through the conduit, connect it to ground at the timer, and replace the bare wire with the green wire. Also, route the ground wire to minimize the risk of accidental contact with either of the hots.

Screw the matching nut to the J shaped electrical fixture for the ultimate in physical protection for your electric circuits, then screw on the motor's back plate with a screwdriver or wrench as appropriate.

Last but not least, reconnect your water piping to the motor. Hopefully you have some sort of union arrangement to make this easy. I've decided to go the flexible piping route. It's not pretty, but it makes maintenance much easier. Be sure to use teflon tape, and over the teflon tape use a coating of clear RTV silicone adheasive sealant.

Reassembly on an Unmovable Pump

Most people have their pump baskets snugly and securely glued to 1.5 inch or 2 inch intake and outflow pipes. The pump is unmoveable. Under these conditions, you need to work at the basket's location and hope for the best.

If you have more than 5 inches of clearance at the back of the pump, just press on the diffuser and carefully guide the pump into the basket assembly after checking and lubricating gaskets. It's not as easy as doing it on a service bench, but it's not terrible either, and at least you won't need to disconnect the electrical wires (just be sure to turn off the juice at the circuit breaker and measure that the voltage is zero).

If you have significantly less than 5 inches but more than 3 inches clearance at the back of the pump motor, you'll probably need to put the diffuser in the basket assembly and then guide the pump onto the diffuser. This will be difficult and require a lot of trial and error, probably including pulling it out and reseating the basket gasket. I saw a pool professional take over an hour doing this, and he cussed and fussed the whole time. You might consider repiping, especially if your setup is overgrown with fittings and patches.

If you have significantly less than 3 inches at the back of the pump motor, you cannot remove or reattach the motor without disconnecting the basket from the piping, which usually means at least a minor repiping job. Keep in mind you'll have these hassles every time you need to remove the pump for diagnostic or other reasons. Repiping isn't that hard, especially if you use flexible pipe on both sides of the pump. I decided to use flexible pipe primarily on the intake side, because it's less likely to pop off or explode there, and even if it fails there, all it does is burn out the pump. A failure on the outflow side could drain the pool, causing the pool to float and break.

You can see details of my repiping job.

The Quick Electrical Disconnect

I heard one suggestion that sounds interesting. Use an inch of rigid conduit to mount a waterproof electrical box to the motor, and run the wires from the screws into the box. Then put the conduit from the timer to that box, and wirenut the wires from the timer to the corresponding wires to the pump. Now you can connect and disconnect the electrical connection in a matter of minutes, even in tight spaces.

I've heard conflicting opinions as to whether that solution meets code. I decided not to do it because I'm not sure if it meets code, and I feel very squeamish about wirenutting a ground wire. If that wirenut connection should fail, all manner of mischief could occur, including the body of the pump being 120 volts with respect to ground, or a backward "sneak path" of unbalanced dual phase electricity.

What I did instead was make the conduit a little longer than necessary so I could move the pump away from the piping (which of course is union disconnectable) before unhooking the wiring.

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