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 prior to removal from the system. Aside for some corrosion on one of the dome bolts, nothing looks too bad.
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.
Upon removal of the spring dome, a pile of rust dropped on the ground to
reveal a badly decomposing assembly.
One very rusty spring, with a membrane in an equally poor condition.
Another picture of the spring and membrane, after I tried some CLR to release the center bolt. That didn't work.
The bottom access ports, left one is the valve assembly, right one is the fliter assembly.
The first port reveals a very gunked valve.
The screen was cleaner than I thought it would be.