Delayed High Pressure from Cat 3535

[Rudy]

I can't figure out why the output of my 3535 is slow to hit 1100 psi like normal. I have cleaned both of the output solenoids (one for undercarriage, and one for the high pressure arch)....and I've even replaced one completely as a precaution.

When the pump comes on (undercarriage for instance), the output pressure goes to 400psi for about one second. Then it's as if something else opens and it goes to 1100 psi which is normal.

I've "exercised" the output bypass regulator (higher, and then lower, and then back to 1100 psi)...and nothing changes.

It seems like the output solenoids are balky opening. But if they stuck closed for one second....wouldn't the pressure come up to 1100 psi with nothing coming out....and then...the balky solenoid would open allowing flow?

If the output solenoids were temporarily sticking closed, wouldn't the bypass regulator open up and regulate to 1100 psi....or does it go full open....and thereby allowing the pressure to stay at 400psi ?

I'm even curious about low voltage to the coils. I'd think that they'd either work, or not work rather than opening slowly....yes?

 

[cantbreak80]

It sounds like the outlet plumbing has a leak somewhere, allowing the plumbing to drain between applications.

Pressure is created at the tip(s). If the outlet plumbing is empty it will take a few seconds for water to fill the line and for the pressure to build to the desired setting.

Look for a loose swivel or a pin-hole in the plumbing that’s allowing the “thumb to come off the straw.”

 

[Waxman]

Maybe you have a blowdown (freeze protect) cycle that is purging lines of water and that is causing the delay.

 

[Rudy]

It turns out that your "thumb on the straw" theory might have been right on.

My undercarriage flush is fed by one hose which branches into left and right sides in the middle of the automatic bay. I think water (might??) have been siphoning from the left side to the right side....leaving a lot of unfilled pipe.

I installed a check valve on the left and right side which should stop the siphoning. I didn't find a leak per se. It didn't do this before...and I don't know why it started doing it now???

It appears OK for now...and will give it a couple of days to see.......

Thanks.

 

[Waxman]

could be a soleniod leaking by a bit etc. that caused the siphoning effect. happens over time sometimes.

 

[Rudy]

Ugh....it's back. This time on BOTH cycles....undercarriage and normal wash.

I'm starting to look at things that would be common....the pump....a restricted inlet etc...

Ideas are always welcome......

 

[cleaning up mud]

do you have a (soft start) valve like a dema valve that reduces the pressure to things like undercarriage or even some have one so the pump does not have to start under such high pressure then increases.

 

[JGinther]

What type of machine is this? If it is a machine that has air blowdown between cycles, you may have a bad check valve allowing air bubbles into the pump. Its common problem on older D/S machines. In my experience it is better to add a hp check valve on the outlet of the pump than to expect the suction line check valve to seat everytime.

 

[cantbreak80]

Somehow the bay plumbing is being evacuated...
1. Air blow/ out winterizing?
2. Lp chemical with air assist?
3. Leaking swivel?

1. Normal operation
2. Air solenoid leaking...adding air to the plumbing during idle times
3. Some swivels don't leak water under pressure. But, allow air in when pressure is off.

After pump cycle watch for water draining from the nozzles for more than a few seconds, you've likely got a bad swivel.

 

[Rudy]

Problem seems to be getting worse.

Now the pump seems to go to about 200 psi for an extremely short time.....then goes to 400 psi for a somewhat longer time.....and then completely to 1000 psi.

The pump in question has over 4000 hours on it. I don't think the valves have ever been replaced. I replaced the seals three months ago.

How do you know if the valves need to be replaced? Could this be my issue?

Also....

There is a very small "drip" on the inlet side of the plumbing. When I say small.....you get a drop every 5 minutes or so. We've placed a pan under it....and you might have an inch or so in it after two months. The leak is in a very inaccessible area to replumb...so we've been reluctant to tear things apart to get to it. I figured that since the inlet is being "flooded" continuously via gravity feed....it's more of a nuisance from the drip than it was to causing a pump issue.

 

[MEP001]

The only way a leak that small could be part of the cause is if it's also allowing air into the plumbing for the lines after the pump to drain empty and have to refill. Does the delay in pressure happen every time, even if it's turned off after running full pressure and immediately turned back on? If it still delays, that eliminates any kind of leak as the culprit.

I doubt the valves are the problem - it would pulsate but shouldn't cause a delay like that.

Is there a regulator, unloader or safety pop-off that could be hanging open?

 

[Rudy]

I agree that a leak that small shouldn't be the cause. That's because it's constantly flooded....yes?

Someone suggested that the belt might not be tight. It was replaced one year ago...and feels tight. I'd think that if it was slipping....you'd hear it.

The only regulator is a Giant 22105. I'd think that this thing would (if anything) stick closed...and not open. If it stuck closed, I'd think that the pressure would go high. I can't see how it'd stick open....and then close and start regulating.

 

[MEP001]

The belt needs to be really tight. You won't necessarily hear it slipping. If it deflects at all by hand, it's loose. Another telltale for slipping will be black rubber powder around the pulleys.

 

[Rudy]

Problem SOLVED.....Finally.

Like I said earlier...my Cat 3535 basically branches two ways....either to the "Undercarriage" or to the "Arch". Each branch has it's own Dema High Pressure solenoid.

I found a problem with the "Arch" solenoid....and it wasn't closing like it should. My system "prepurges" presoak soap during the undercarriage cycle, so it was hard to tell that some undercarriage pressure was "leaking" to the arch.

A new spring in the Arch solenoid fixed matters. It now stays closed tightly during the undercarriage flush...and now there's no delay.

My thanks to everyone on this forum.

 

[M7T]

How is the plumbing on your Cat Pump?
Check the outlet, if you have a recirculating adjustable valve that takes the extra pressure back to the cat pump may be broken.
Can you post some pics to see how is the outlet line at the Cat Pump? If that happens with the UCW and the machine, seems to be a problem in the pumping plant, hopefully is not the Cat Pump.

 

[MEP001]

He had his problem solved some time ago.

 

[mac]

If you have a small leak on the inlet, that is most likely the cause. If it's leaking when not running, it will suck air in on start up. Fix it now or it will get worse.

 

[Rudy]

Thanks. Again...the problem was solved. There was a bad spring inside one of the two solenoids. It was allowing "bypass" until it finally worked it's way closed. The spring should have held it in the closed position....but wasn't.

There's always a reason why....yes?