SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I got a 3/4" supply line coming from a pump room to a backflow inside the building and then the 3/4" line is then coming outside to another backflow on the outside of the building. The problem I am having is that I have 42 psi at the sprinklers but then after a minute of running the sprinklers the pressure drop to 24 psi. Sometime it will go back up to 42 psi but then drop back down to 24 psi and sometimes it even goes almost to 0 psi. Could the second backflow be causing the pressure to drop? I'm stumpped, does anybody have any idea what the problem could be?

The pump are suppling water for a muti story hotel. The only other things that are running off the same water line are 2 wash machine. If I turn the system on early in the mourning I still don't have much pressure. The backflow inside hasn't ever been tested either. So do you think that it is a pump pressure problem then?

Which it does from 42 psi to 22 psi. But sometimes it drops near 0psi, is this maybe because the pumps aren't on at the time it nears 0 psi?

Well I think I've figured out what the problem was. The pressure before the inside backflow was 42 psi. the pressure after the backflow was 22 psi. The problem I think is that the backflow has never been serviced in the last 6 years it has been in the building. It must be sticking inside, that what I think is the problem. If it get serviced and it doesn't work then, I will be really scatching my head then! Thanks for your help though guys.