I just rebuilt my Zurn Wilkins 600XL 1" pressure regulator, but it still is not controlling the pressure after rebuild.

One thing I notice is if I measure the pressure immediately after closing a running faucet, I'll see the pressure slowly rising till it gets to abt 110psi (which I assume is city pressure levels).

I pulled it apart again after re-installing, and I noticed two large chips in the bore where the stem unit sits. The chips straddle where the O-ring sits in the bore (those black lines in the center of the bore is residue from where the O-ring sits).

Chip #1 Chip #1 - zoom in Chip #2 Chip #2 - zoom in

The regulator core sits facing a wall, so I couldn't see the chips the first time I re-assembled. I could only feel the roughness manually w/my finger, but I ignored it. It wasn't till after the unit was re-installed and still not regulating that I started wracking my brain to think what it could be. The roughness I had felt was the only thing I could think of, so I decided to go back in and actually turn the valve unit so I could see into the bore, and that's when I noticed those big chips.

This YouTube video says that bore needs to be smooth to for the regulator to function properly: How to Repair a Water Pressure Regulator | Zurn Wilkins 600XL (https://youtu.be/eI334pzRWDQ)

My theory is that those chips in the bore are allowing water to bypass the O-ring, and so not adjusting the water pressure; a little bit of water slowly seeps through those chips raising the pressure in the house system till it reaches parity with the city pressure.

This theory is inline with the behavior I saw where the pressure slowly increases when measuring immediately after closing a running faucet.

I can't explain how those two large chips got there in the bore, though.

I'll go to hardware store today and buy a whole new unit, and see if replacing the whole thing fixes the issue.

My questions are:

  1. Are those chips causing the regulator to not regulate the water pressure?
  2. What could have caused those chips? How could they have got in there?
  • O-rings are use to seal, but need smooth surfaces of the right size/distance. Those chips defeat any sealing the o-rings could do.
    – crip659
    Commented Feb 19, 2023 at 0:22
  • Thank you ver much!
    – SDSHuge2.0
    Commented Feb 19, 2023 at 1:15

2 Answers 2


After replacing the core, the pressure can be controlled with the adjustment just as expected.


enter image description here

  • It would be helpful if you would give your answer the check mark so others know this has been resolved. It may help someone else who is having a similar problem.
    – FreeMan
    Commented Mar 21, 2023 at 16:44
  • 1
    @FreeMan - checked
    – SDSHuge2.0
    Commented Mar 22, 2023 at 9:17

I expect the damage was caused by some bits of grit in the water supply that were not filtered out (many of these pressure regulators have an input screen for that purpose) which became trapped at the edge of the o-ring and then ground up and down as the piston moved until they wore grooves in the wall, causing failure.

If you need to provide a separate pre-filter due to not having one built in, be careful to select one that will stand the high input pressure.

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