Autopsy of a 35 Year Old Watts 25A Pressure Regulating Valve
August 27, 2010

Two weeks ago, the pressure regulating valve in our 35 year old home died.  Here is a pictorial autopsy of what a failed Watts 25A regulator looks like.  At first, when I realized we had a bad PRV (Pressure Regulating Valve), I actually considered trying to find a rebuild kit.  I am glad I didn't.  Later I also found out that Watts discontinued this model around 2003, so repair kits aren't available for it anyway. 

A bit about the root cause of the failure.  The symptom was simple: when water was flowing, the pressure would drop to about 50 PSI.  This is expected as the valve must open in order to allow water through and the more it opens, the lower the pressure.  When water flow is halted, the pressure would bump up to static pressure of about 60 PSI.  At that point, it would immediately start creeping up to about 95 PSI within about a minute.  At the time I didn't know that 95 PSI was actually the house's supply pressure (input to the PRV).  If you research this problem, you will see two potential things blamed for this: lack of expansion tank when a hot water heater is installed, or a bad PRV.  The easiest way to eliminate the former is to turn the water heater off.  By turning doing so, it eliminates the ability for water to expand and increase the static pressure.  Note that there is no need to drain the hot water already in the heater, since it's already expanded.  If the water heater is turned off, open a faucet for a few seconds. The pressure should drop to the PRV's pre set pressure and hold.

There are two possible failure modes for the PRV: bad diaphram and leaking valve.  In my case, I could not completely disassemble the spring-diaphram-valve assembly, but I am convinced it was a leaking valve.  There are two reasons for that.  If the diaphram was leaking, water would accumulate in the spring dome and eventually leak out of the pressure adjustment bolt.  This never happened, therefore this scenario is eliminated.  The second and most likely failure is a leaky valve.  As you can see from the pictures below, the valve was heavily coated with mineral deposits, and therefore it wasn't sealing properly and the leakage would slowly but surely equalize the house pressure with the street pressure.

I don't know anyone that checks their PRVs on a regular basis.  It's probably wise to check it once every few years.  Click on any of the thumbnails below for the full size image.

Watts 25A PRV
Watts 25A prior to removal from the system.  Aside for some corrosion on one of the dome bolts, nothing looks too bad.

Watts 25A PRV
Closeup of the manufacturer's tag. I find it interesting the the model number (25A) is listed under "NO." and the "MODEL" field is blank.

Disassembled Watts 25A PRV
Upon removal of the spring dome, a pile of rust dropped on the ground to reveal a badly decomposing assembly.

Watts 25A PRV rusted spring
One very rusty spring, with a membrane in an equally poor condition.

Watts 25A PRV
Another picture of the spring and membrane, after I tried some CLR to release the center bolt.  That didn't work.

Watts 25A PRV
The bottom access ports, left one is the valve assembly, right one is the fliter assembly.

Watts 25A PRV
The first port reveals a very gunked valve.

Watts 25A PRV
The screen was cleaner than I thought it would be.

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