Cat 310 not building pressure

[Creole]

Hello all,
Scratching my head about a pressure issue I’ve not seen before. One of my pumps has mysteriously lost pressure. Seals only had about 400 hours when the pump pressure dropped to 1000 pounds from the 1500 we normally run. First thought was a new tip, no change, the pressure regulator would not bring the psi up, so I replaced it. Again no change. Decided to rebuild the pump head, which involved changing the head because one of the seat retainers would not come out. New seals and different head, still no change. New valves, looked for inlet obstruction, changed the pressure gauge, hot water, cold water, tightened the belt, verified that all the plungers are stroking. The best that pump will do is 1000 psi. If the wand trigger is not pulled (weep guns) it will rise to 1500, which indicates a flow problem, but I’m stumped! The only thing left for me to check is pump rpm, but honestly in 27 years as an industrial control tech, I’ve never seen a 3 phase motor run slow. It’s rather all or none unless it drops a phase, but that’s not the case here either.
Thanks in advance for any and all help!

 

[MEP001]

Look for a bad check valve. Typically you have at least two at the boom and one at the pump outlet for weep. If any of those are bad you'll lose flow through it and thus lose pressure. The weep one is easiest to check since you can either unhook the line going to it or look to see if the other bays weep water when the one you're working on is running.

 

[Creole]

MEP001,
Thanks,
I’ve checked the one for the weep, but failed to think about the low pressure check valves. Good thought! I’ll give those a look.

 

[Creole]

My Hat’s off to you MEP001!
thanks for your help. It’s amazing how easy it is to overlook the simple stuff. I was completely ignoring the spot free check valve. Easy fix, thank you.

 

[mjwalsh]

I had the same thing happen about 10 years ago. This thread refreshed my memory!

 

[mac]

If that check valve failed it should hAve caused the low pressure hose to rupture

 

[MEP001]

I don't put a check valve anywhere on the spot free system between the bay check valve and the tank so if the bay check valve fails it backs up into the tank but doesn't cause any harm to the pump or tubing.

 

[Creole]

The low pressure hose didn’t fail because I changed them to copper line after we bought the wash a few years ago. We used to get surprised with low pressure line failures on the spot free system. So I replaced them with copper. But you’re right, it would have been obvious otherwise.
Thanks