Hydraulic riddler (solved)

I have a riddler for you guys. This one had me scratching both ends for a while!

I built a press for a customer that has full-pressure extension on two cylinders, but the bottom cylinder has a low-pressure retract, so it can hit a limit stop without crushing the stops (30T actual working force at full pressure).

The bottom cylinder simply has an in-line relief valve in the retract circuit to limit the force, and the relief was set for 250psi, with

2800psi on the high-pressure sides of everything else.

Facts:

- I adjusted the relief valve for 250psi before the press shipped.

- I use an 11gpm test hydraulic supply, the customer has a 30gpm supply; same top-end pressures

- The relief valve I ordered was a 250-2500psi valve. It turns out they shipped me a 700-3000psi valve. I did not notice when I installed it. It adjusted just fine to 250psi.

- The press has worked to spec for the last month, up until this morning. Today, the bottom cylinder started to creep up after being retracted, AND it was 'balky' at retracting. Now, usually hydraulic problem symptoms (except catastrophic leaks) don't happen suddenly...

The customer helped me trouble-shoot over the phone. He's in Montana, I'm in Florida. I told him either the control valve was bypassing excessively (not likely) or the relief valve was leaking -- probably (very likely) some chad in between the ball and seat, since he had to do some field plumbing to install the press.

He knows a little about hydraulics, concurred, and inspected the control spools and the relief valve. The spools were in good shape, and felt "lapped to fit" (as they should). The relief valve had NO check ball in it.

HUH? It worked YESTERDAY. It has to have a ball in it!

It didn't, and a new ball fixed the problem.

What was the problem? (solved; we have the original ball, now).

(better'n Car Talk, huh?)

LLoyd

Reply to
Lloyd E. Sponenburgh
Loading thread data ...

Wild guess - over adjusting the 700-3000 relief valve down to 250 opened it up enough that after some wear and shock loading the check ball was forced past the adjustment mechanism and ended up in the return filter or tank?

Reply to
Pete C.

"Pete C." fired this volley in news:4fc5805c$0$2982 $ snipped-for-privacy@newsreader.readnews.com:

Good guess! It ended up at an elbow in the 1-1/4" return line.

HOODA thunk they'd have made a valve so the ball could fall out the tank line! F'gosh sakes! All they had to do was put a bar or block of some sort across the tank fitting so the ball couldn't ever come out...

Dang! It cost them a day down, and me nearly a heart attack. I could NOT envision myself shipping that unit without having checked the retract pressure.

It was the flow that did it. My 11gpm supply just wasn't enough to push the ball off the end of the spring, but 30gpm was.

Worse -- some checking reveals that their 700-3000psi valve is _rated_ to be adjusted down to as low as 250psi, so there are no excuses. BRAND hydraulics is getting an angry call tomorrow!

LLoyd

Reply to
Lloyd E. Sponenburgh

Does your brother build machines better than you do?

Reply to
Bob La Londe

"Bob La Londe" fired this volley in news:1_gxr.16557 $ snipped-for-privacy@newsfe11.iad:

Don't build machines like my brother!

Lloyd

Reply to
Lloyd E. Sponenburgh

Is it rated for flow?

Weird. Or stupid. Or something.

Reply to
Tim Wescott

Tim Wescott fired this volley in news:Hd2dndYNYZ_

311vSnZ2dnUVZ snipped-for-privacy@web-ster.com:

Yeah. They were within the flow rating at the time it failed. Their pump _can_ exceed the flow, but they had it dialed down.

I called the manufacturer. They had heard of the problem, and had issued a new, longer but lighter spring for the low pressures. They are also considering adding a "caging" screw that protrudes into the tank port just far enough to prevent the ball from "washing" out of the valve.

Good idea, I think!

LLoyd

Reply to
Lloyd E. Sponenburgh

And Not A Moment Too Soon.

--Winston

Reply to
Winston

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.