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BackFlow Preventer Pressure Drop

R

Rudy

Active member
I have 60 psi coming into my car wash via a 2" supply line. There is a 15 psi pressure drop across my Watts RPZ 909 backflow preventer.

I am now getting a low pressure trip on my RO machine when all of my pumps kick on during busy days.

Isn't this amount of pressure drop excessive? Would a rebuild (seals only or what?) help?

Has anyone rebuilt a RPZ unit? It doesn't look to tough after looking at the diagrams.
 
I rebuilt mine, it was pretty easy. Now rebuilding one and have it not leak...a different story. Our buddy Randy is pretty knowledgeable about them and helped me out, but all in all it was pretty straightforward, nothing to be intimidated by.
 
Would the rebuild fix my pressure drop problem?

Or.....do they need to be rebuilt when they fail a backflow test?
 
Rudy said:
Would the rebuild fix my pressure drop problem?

Or.....do they need to be rebuilt when they fail a backflow test?
Click to expand...

I rebuilt mine because it leaked real bad. When finished, it didn't leak as bad. After 3 or 4 years it was leaking real bad again so I got another kit for it. When I got a chance I took it apart to install the kit and found a broken valve cage. The valve was not part of the kit and the closest one was over two hours away. I couldn't get it back together without a new valve so I hopped in the truck and drove to Cincinnatti and picked it up. Got it back together and reopened the wash that evening. It still leaks a little.

I have no idea if this will take care of your pressure issue.
 
Are you sure it's the RPZ valve that's the issue? You'd need to install gauges on the ports and watch it. Typically when there's a problem they don't affect the pressure through, it just leaks.
 
If your RPZ is causing the problem, your water department might let you use another device such as a double check or pressure vacuum breaker. The double check uses 1lb. springs in the check valves vs. the 5lb. spring in the first check of the RPZ.
 
I found a strainer just before the backflow preventer. I have NEVER cleaned it in 16 years. I was anticipating finding my problem.

It was clean as a whistle. Perfect. The problem does indeed lie somewhere else.

Flow and pressure can be confusing at times, since Static vs. Moving water changes things.

Is it correct that I'll see the biggest pressure drop just after a flow restriction, when the water is flowing? If the water is NOT flowing, the static pressure in the line should be essentially uniform.....yes?
 
Rudy said:
Is it correct that I'll see the biggest pressure drop just after a flow restriction, when the water is flowing? If the water is NOT flowing, the static pressure in the line should be essentially uniform.....yes?
Click to expand...
It's not a restriction from an orifice. It works like a regulator. The water pressure after the valve should be uniform unless the supply before it is insufficient.

Again, the only way you're going to determine the problem is by using the test ports with gauges.
 
Pressure Drop

Rudy said:
I have 60 psi coming into my car wash via a 2" supply line. There is a 15 psi pressure drop across my Watts RPZ 909 backflow preventer.

I am now getting a low pressure trip on my RO machine when all of my pumps kick on during busy days.

Isn't this amount of pressure drop excessive? Would a rebuild (seals only or what?) help?

Has anyone rebuilt a RPZ unit? It doesn't look to tough after looking at the diagrams.
Click to expand...

Your issue may be related to volume and not pressure. You may have a strainer in line prior to the RPZ. If it has any debris it will drop volume which coul be related to you having problems at full capacity.
 
I replaced all the media in my water softeners, and a LOT of the pressure drop issues went away. The resin was original in my wash (18+ years).

Now, the only time the RO drops off due to a pressure problem is when EVERYONE at the wash fires up a high pressure selection....including both automatics. This isn't often and means we are having a Killer day!
 
I had the same problem, and the only way to fix it was to install a booster pump after the city required backflow RPZ. works like a champ now. And yes I also had a 15psi drop. Also had a drop in my water softener that also added to the problem.
 
We didn't have a large enough water line to the car wash for the automatics so we added a booster pump before the back flow valves to push the water through the valves. We were afraid that the valves would starve the inlet of the pump. We also have bladder tanks. The pump runs when the HP auto runs.
JIMT
 
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