There has to be something I'm not following here. If you have the
installation as you describe it with just the two check valves, the
system will dump all system pressure as soon as the pump shuts off.
Yes, we are both on the same page now. In my system, I use it
for a sprinkler system and , if I mount the backwards check valve
at the foot strainer, the system would drain back and lose its
prime every time, just as you say. I was trying to simplify it,
--- a shame I can't make a simple sketch on the newsgroup.
In effect, my "reverse" check valve (which releases the sytem
pressure) is put onto a tee right at the pump inlet, AND elevated
a couple of feet ( 1 foot - 1/2 psi ) higher than the pump.
Now, the entire outlet pipe will drain down until the water in it
is at the same height as the reverse check valve. That way the
suction pipe remains filled, with a couple psi in it to help seal the
check valve at the foot. Sorry that I was inaccurate in my
I had thought that the method and technique would be obvious, but
I guess I must have mixed up the explanation...
Remember, the system will drain (depressurize) until the head
in the system is the same as the head of the elevated reverse
check valve. In a sprinkler system, it's non critical. If you have a
tank system, you have to make allowances for what you want to
Some people put two NORMAL check valves in the intake
suction pipe -- one at the pump inlet and one at the foot valve.
I don't like that since I have a big drop between the pump and
the foot valve, and the increased tension in the second check
valve seems to really cut down the amount of suction lift
I can handle. I'm not sure why, but it seems to be a LOT
worse than with just one check valve. I mention this just
for reference, and that other designs I have seen have
cautioned against two normal checkvalves in the input line. I guess
they had the same problem (grin). They didn't say why,
Again, I am sorry I wasn't clear in my explanation. A picture would
be worth a thousand words here.
Andy in Eureka, Texas