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What to Do if a PVB Backflow Preventer Won't Stop draining Water from Under the Bell

Simple and quick things first. If pressure was lost and restarted at some time it’s possible that trash is lodged under the seal. Turn off the main feed valve to the PVB. There should be a “T” handle on the supply line. Water should stop flowing. Open the test petcock on the side for a moment to drain the water in the PVB. Close the test petcock. Now turn the valve on QUICKLY. The system depends on water pressure to seat the seal. If you turn it on too slowly it may not seat correctly. Expect water to leak for a few seconds after you turn it on. That is normal. If it continues then we have a problem.

If it continues to leak from under the top bell then the assembly needs to be rebuilt. This is a simple procedure, no special tools are required, and rebuild kits are readily available. For a video on how to rebuild one look HERE.

To repair it yourself, first turn off the water. If you don’t your life will get real exiting real quick. Now you start by removing the top nut. Set it and the bell cover aside. Under the bell cover you see the bonnet. Unscrew it. If it is stuck you can use pliers or a screw driver to move it around. DO NOT SCRATCH THE BRASS. BE CAREFUL. If you scratch the brass threads you may need to buy a complete new unit. If you have a hard time getting the bonnet out, go back and watch the video mentioned above. It’s well worth it for removal hints.

The poppet should just lift out. Take a quick look inside to make sure there isn’t any trash sitting around. Do not remove anything else. Do not play with the spring. Resist temptation.

Now simply reverse the procedure. The bonnet and top nut should go on firmly but don’t over tighten. Now turn on the water. Remember, it will leak for a second or two while it seats then it will stop. That’s all there is to it.

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