SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I have a 1"" Watts 009 QT valve with a small dripping leak out the vent on top of the cover. I removed the valve top to replace the diaphragm stem O-ring but couldn't access it because the diaphragm was stuck to the the valve top around the OD where it seals.

Any suggestions on best way to remove the diaphragm from the top without damage to the diaphragm?

Was able to remove the diaphragm without damage using an exacto knife very carefully. Unfortunately, the o-ring dimensions I got from Watts were wrong. I put the top back on, following instructions. When I opened the inlet valve (with outlet valve closed) water gushed out the relief valve dump. I removed the top and tried again. This time, no water from the relief valve. Could this have been caused by air in the valve? I did not open any bleed screws either time. I did notice the top vent leak slowed to almost nothing while the sprinkler was running, but still dripped when the sprinkler was off.

So, called Watts and this time got dimensions for the diaphragm stem piston o-ring which agreed with the rough dimensions of the old o-ring. I'll try for the third time with a new o-ring. There was some green buildup in the o-ring bore which I tried to clean out but did not get all of it.

The correct o-ring was installed on the diaphragm stem piston after cleaning up the bore in the valve cover. It still had a dripping leak out the vent. The bore the o-ring seals in has some pits. Tried to clean up bore with fine sandpaper. Still leaked.

The old seal is square. Watts says this is due to deformation over time but it looks to me like it started as a square ring rather than an o-ring. Looks like a square ring has a better chance of sealing.

Is there any practical way for me to repair the pitted 5/16 dia bore? The valve is approx. 19 yrs old. A new cover costs $80.

I agree. If I hired someone to repair it, they would recommend replacing it and would have many years ago as well. If I replace the top to stop the drip, what would likely be the next problem? What is the downside of repairing it at this point?
Nothing is injected into the sprinkler system. Per the city inspector, a double check valve could also be used if it had an intermediate atmospheric vent.

I am retired and do all maintenance and repairs I can around the house. Have been able to do all the lawn sprinkler repairs and almost all appliance repairs.

Thanks for your replies.