Low Dynamic Pressure
I'm having an issue with low dynamic pressure in my irrigation system. The tech who opened my system recommended increasing the pressure at my PRV however if I raise the pressure above ~70psi I get terrible knocking/banging for 5-10 seconds when starting any zone in my system.
At 70psi static I get no knocking on startup however when a zone is running I get low dynamic pressure. I have two easy measurement points, one is directly after the PRV before the T for my irrigation system, the second is after the irrigation T between my RPZ and master valve. From a GPM standpoint if I remove a head from my rotor zone and just let water flow freely I get ~14-15gpm.
Static Pressure:
After PRV: 70psi
After RPZ: 60psi
Dynamic Pressure w/ 6 rotor zone (14 GPM demand):
Actual GPM: ~8.5gpm
After PRV: 46psi
After RPZ: 26psi
Dynamic pressure w/ 6 spray zone:
Actual GPM: ~6.5gpm
After PRV: 50psi
After RPZ: 30psi
The house is ~1 year old so this is only the second season for the irrigation system. Things were working well last year so I didn't take extensive notes but I'm almost sure the 6 rotor zone was closer to 12-13gpm when running last year.
If it matters my main service is 1" which goes down to 3/4" through the meters, prv, backflow, etc. and then back to 1" PVC for the irrigation system.