Pressure Loss Question


Last year, I tested the pressure at my various rotors and found the pressure to be around 65-70 psi

To remedy this, I had a PRV installed set at 50 psi

This morning, I went out to test my rotors and was shocked to discover that they’re all at ~20 psi

I proceeded to double-check the pressure at the drain spigots in the basement and outside, confirming that they’re both around 50 psi

What could cause such a pressure loss between the supply and the rotors?

I don’t think that I have a leak as the loss is observable on multiple zones and I don’t seem to have a giant wet spot that I can see

Any thoughts?

I think if the rotors are pretty far from the PRV that could cause pressure loss but I have never done the math to see how much of a run would cause significant loss.

I don’t think that the rotors are terribly far - one is virtually on top outside drain spigot

Although, while I do admit that I don’t know the route(s) of the trunk piping, it seems to me that if the loss was a result of the piping lengths, wouldn’t the rotor closest to the drain spigot have much higher pressure than those further away?

That’s not the case, as all of the rotors have approximately the same pressure.

Here’s another question - should the PRV be set so that I get the desired pressure at the rotor nozzles, as opposed to at the drain spigot?


I have seen some constant pressure vacuum breakers with up to a 20 pound spring in them. That means you will loose 20 pounds before you get to the manifold. Also the breaker needs to be one foot higher than your highest head which can increase the pressure loss before the manifold. Double check valves are usually around 5 pounds for each check spring (10 pounds total) but can be inline with the rest of the plumbing.

So I just tested things again

At the spigot while water flowing - 50 psi, as before

But now, at the same rotors as yesterday - 42-45 psi

What could have changed?

Were you running anything else while doing the first test (other zones, shower, washing machine, etc.)? Besides that the only other thing I can think of is that the water supply for your city has fluctuations in water pressure.

No, I don’t believe any other water was being used…

Putting that aside, since the water pressure at the spigot was the same both times - shouldn’t the rotor pressure be somewhat similar?

Yeah that’s true. I have no idea what could cause this then.