Pool Pump Shaft Seal Replacement

how to change a pump shaft seal
Rob Cox August 19, 2015

The last two blog posts were an effort to try something new; lighter topics in the style of "fluffier" blogs or "news" feeds. I see from the blog visitor statistics that our audience prefers something more substantial, something useful - not fun facts and celebrity pools.

Thank You! We now return to the topics that most interest you - technical topics with some meat on it! We'll start off with a problem that most every pool owner can relate to - a leaking mechanical shaft seal, how to identify it, and how to repair it, too. Just giving the people what they want.


The shaft seal prevents water from leaking along the motor shaft, just behind where it connects to the impeller. The motor shaft goes through the seal plate, or the bracket that connects to the pump. The design of a shaft seal allows the shaft to spin without any direct contact (which would immediately cause a seal failure with the shaft rotating at 3250 RPM).

Shaft seals (#7) are composed of two halves, a round ceramic ring encased in rubber (what I call the Donut), and the other half with the spring, or the Spring Half. The donut usually sits in the seal plate (#3), and the spring half slips over the impeller (#8). As the impeller is tightened down, the spring half mates perfectly with the donut half, sealing up the shaft from water leakage, without actually touching the shaft.


Shaft seals are constantly immersed in water, and although they are constructed of high grade stainless steel and chemical resistant rubber, chemical degradation can take a toll. Over time, near constant low pH or high chlorine will break down seal materials, and cause a shaft seal to leak. Ozone can also damage shaft seals, but not when installed properly.

Another cause of seal failure is running the pump dry, or nearly dry. With very little water running through the pump, the water inside gets very hot which can melt and warp some shaft seals. This usually happens from a loss of pump prime from low water level, stuck skimmer weirs or a large air leak in front of the pump.

A third cause of shaft seal failure is caused from a water hammer effect. This can happen if you start up the pump in spring without taking the return plugs out of the wall, or from closing a return side valve suddenly while the pump is running, or turning the multiport to backwash without turning the pump off first. This is known as a "seal blow-out", and that's exactly what happens, the seal cracks or becomes dislodged from the seal plate.


Good question, shaft seals aren't labeled, and you want to have the correct shaft seal in hand before you open up the pump. They are somewhat standard; there aren't dozens and dozens used on residential pool pumps. The most common shaft seals are #100, #200, #201 and #1000.

You can find the correct shaft seal by visiting the schematic pump parts diagram for your particular pump, or you could just use the handy common pool pump seal chart that I created, just for you. Click it to view the larger image.


If it's leaking, then it has reached the end of a hopefully long service life. A leaking shaft seal has a particular signature leaking style all its own, and should not be confused with two other types of pump leaks. Water around the pump could also be leaking from the PVC plumbing fitting on top of the pump, which runs down and drips off of the bottom of the pump, right below the shaft seal. A loose clamp band or oring on the seal plate can also cause a pump to drip on the ground - directly below where the seal would leak. 

Don't be fooled by a loose clamp band or PVC fitting! A shaft seal that has failed will leak water between the motor and the seal plate, where the donut half of the seal sits. The water runs down the back of the seal plate for an inch or two, before dripping off onto the ground. Pumps with open brackets are easy to see if the seal is leaking and may be spraying wildly, but most leaking shaft seals are hard to see, unless you get your head on the ground with a flashlight. Most failed shaft seals will leak whether the pump is on or off, but will leak more with the pump running.Click the image to see two examples in a (much) larger image.


First, obtain a new shaft seal. If you can't wait to order it online, pick one up at a local electric motor shop.

  1. Shut off the pump at the timer and breaker. Be sure that it won't be turned back on during repair.
  2. Remove the pump clamp band or the 4-6 bolts that hold the seal plate / motor to the pump basket.
  3. Grab the motor (it may be hot) firmly and slide the motor backwards, to pull it from the pump.
  4. Remove the diffuser or impeller cover, if you have one. Remove the rear motor cover.
  5. Loosen the capacitor bracket screw at 9 o'clock, to pull the capacitor out of the way.
  6. Slip a 1/2" wrench onto the rear of the motor shaft to hold it stationary, the shaft is slotted on the end.
  7. Slip large pliers or strap wrench over the impeller, to gently unscrew it from the shaft.
  8. Disconnect the seal plate from the motor, knock out the old donut seal half with a screwdriver.
  9. Remove the old seal half from the back of the impeller.
  10. Clean up the seal plate, impeller and motor shaft surfaces if they are dirty or rusty.
  11. Push the new donut half firmly into the seal plate, using the cardboard piece, to keep it clean.
      (#1000 seals are press fit into place, using a 1" PVC coupling and a small hammer. Before press fitting it, smear a small amount of Blue RTV or similar gasket silicone.)
  12. Push spring half onto impeller; hard plastic end facing the motor, soft rubber end facing impeller.
      (See seal instruction sheet if unclear - a backwards placed seal will leak from the get-go!)
  13. Replace the seal plate onto the pump, and thread the impeller onto the motor shaft.
  14. Slide the motor back into the pump, being careful that the oring makes a good seal.
  15. Tighten up the clamp bands, or if your pump has bolts, tighten all equally and firmly.
  16. Fill the pump up with water, open closed valves and test out your handiwork!


Wow - 16 steps to replace a shaft seal! Some of them only take a few seconds though. Replacing a pool pump shaft seal can be completed in 30 minutes, it's not usually complicated. The hardest part for most people is getting the impeller off - that's steps 5 and 6 - you have to hold the shaft stationary, so it won't move as you spin off the impeller. After that is conquered the next pitfall is usually putting the seal in backwards. Take a good look at how the shaft seal is oriented as you remove the old donut and spring halves, and refer to the included diagram, when included.


- Rob