How To Replace A Pool Pump Diffuser


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The location of the pool pump diffuser is shown in this cut-away of a pump. The pool pump diffuser surrounds the pump impeller. It's purpose is to control the flow of water to and from the impeller. For a more complete discussion of the function of the diffuser click How A Pool Pump Works. Sometimes hard debris will get into the pump and will crack the diffuser. In other cases the threads that hold the impeller to the motor shaft become worn causing the impeller to wobble and rub against the diffuser. This guide explains how to replace a bad pool pump diffuser in a Hayward Pump, however, the pool pump's parts and it's operation are common to most pool pumps.

Things You'll Need

Step by Step


Step 1

The first step in preparing to remove your pool pump's diffuser is to turn off all power to the motor. For maximum safety turn off the power at the circuit breaker to the motor - usually located next to the timer box.

Step 2

Next you will have to relieve the pressure that builds up in the pool pump during operation. To relieve pressure turn the relief valve on top of the filter counter clockwise. Water will spray out initally as you see the pressure on the pressure gauge go to 0 psi.

Step 3

To extract the motor pump assembly from the pump housing, first remove the four 9/16" bolts that bind the motor pump assembly to the housing. Keep track of the washers. Note: Some Hayward pool pumps have six bolts.

Step 4

Pull the assembly apart from the housing.

Step 5

After the assembly is out, you should see the pool pump diffuser and diffuser gasket on the end of the assembly. If you do not see the diffuser or its gasket, check inside the housing.

Step 6

If the pool pump diffuser came out with the assembly, pull the diffuser off the assembly. It should snap off easily.

Step 7

Place the pool pump diffuser gasket is on the collar of the new diffuser properly. Put a thin coat of lubrication on the gasket.

Step 8

Snap on the new pool pump diffuser - no screws are required. Ensure that the part of the diffuser labeled "TOP" is aligned with the "TOP" labeled on the seal plate.

Step 9

Slip the motor assembly back into the housing.

Step 10

Replace the four bolts evenly. If bolts were numbered 1 though 4, replace bolts in this sequence - 1, 3, 2, 4 - to ensure that the motor is set properly inside the housing. Loosely tighten bolts in this sequence, then go back and tighten them down again in this sequence. If pump has 6 bolts, replace bolts in this sequence - 1, 3, 5, 2, 4, 6.

Step 11

Prime pool pump by removing strainer lid and filling strainer with water. Replace lid.

Step 12

Reset circuit breakers to start pool pump.

Step 13

Close the relief valve on top of the filter. Wait until after the air is purged and water starts to spray out of the valve.


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InyoPools Product Specialist  Posted: 12/24/2016 

jaywalker1981 - You may have the wrong size diffuser and/or impeller. When you try to select the diffuser or impeller for your motor, you have to look at the motor's total HP which is the product of list HP and SF. See our guide on "How To Understand True Pump Horsepower - Up Rated vs Full Rated". Give us a call at 407 287 5525 if you need further assistance.

 Posted: 12/22/2016 

I am changing the diffuser and the impeller on my sta-rite dyna-glas pump.

I noticed that the diffuser and the impeller fit a "too" snuggly. I can't imagine this is good. But this is the first time I am doing this.

Both diffuser and the impellar are brand new.

Here is a link of the video. Notice the grinding noise when the diffuser is "loosely attached" to the pump.

Looking for any advice on what is going on here.


InyoPools Product Specialist  Posted: 3/8/2013 

screech - Thanks for your comment. Glad we could help and we appreciate your business.

 Posted: 3/8/2013 

Because of your great directions and that you are smart enough to put them there as a sales enhancer, I will purchase my parts from you.

 Posted: 1/2/2012 

Great information on replacing your pool pump diffuser