Big PSI difference at pump when trigger pulled.

[carlmorris321]

Hello all,

I just got a poor Google Review about my pressure being lower than other self-serve car washes so I figured I better reach out to other owners. I noticed that when the high pressure is running on my newest CAT 310 it reads 1100 PSI and then drops to 1050 when the trigger is pulled. However on a few of my older CAT 310's the pressure at the pump reads 1200PSI but then when the trigger is pulled it drops down to 800 or 900 PSI. I just replaced the seals on one of them and it only gained me about 50 psi so the range is 1200 trigger loose and 950 trigger pulled. Why so much difference from trigger pulled to trigger loose? I also changed my unloader and pressure gauge to make sure they were fine. The valves all worked. I would like the pressure in all the bays at 1050 if possible.

 

[edredtop]

Hello all,

I just got a poor Google Review about my pressure being lower than other self-serve car washes so I figured I better reach out to other owners. I noticed that when the high pressure is running on my newest CAT 310 it reads 1100 PSI and then drops to 1050 when the trigger is pulled. However on a few of my older CAT 310's the pressure at the pump reads 1200PSI but then when the trigger is pulled it drops down to 800 or 900 PSI. I just replaced the seals on one of them and it only gained me about 50 psi so the range is 1200 trigger loose and 950 trigger pulled. Why so much difference from trigger pulled to trigger loose? I also changed my unloader and pressure gauge to make sure they were fine. The valves all worked. I would like the pressure in all the bays at 1050 if possible.

I set my pressures when the trigger is being pulled because that's what counts.
You may have bad pressure regulators (bypass) if its too high when In idle. My 310s usually idle at about 150 to 200 psi. My guess is you're using weep guns so your regulators may not be unloading because there's not enough back pressure (and thats ok as long as desired pressure is being achived for customers) Randy has said he uses a tennis ball to keep the trigger pulled when he sets it, I use my wife . (She's awesome)

 

[carlmorris321]

Yeah, I use a spring clamp to keep the trigger pulled. Probably should find a wife...lol It sounds like you use a weep gun as well but instead of measuring unloading pressure, measure the idle pressure further along the line. I would imagine my idle pressure is about 150psi as well (My pressure gauge sits right above the regulator so it doesn't measure idle pressure...). I checked out that other forum and saw someone mentioned the tip. I will check that out tomorrow.

 

[carlmorris321]

I am still learning my terminology here...I don't actually use an unloader. I use a pressure relief valve that bypasses outlet water when the trigger is released and sends it back to the pump. The pressure relief valve works as a pressure regulator essentially. My pressure gauge sits on top of this valve. Also I don't use a weep system that sends a constant trickle when the pump is off. Just a weep gun that sprays low pressure when the trigger isn't pulled.

 

[Greg Pack]

I try to start with simple stuff:

worn nozzle or different nozzle size?
belt slippage?
inlet restrictions(usually results in pulsation)?
water escaping to the weep system due to a bad weep check valve on that bay ?
I know you said you inspected the valves but worn valves can cause lower pressures. Is this an old pump on the busiest bay?

I've also had unusual restrictions between the pump discharge and nozzle tip- small plumbing, etc. A few years ago I had a strange drop in pressure on one bay and actually had to replace the HP hose to the bay to get the pressure back up. If you can swap hoses in the equipment room to flow water to another bay this will allow you to test for that.