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?)G

LLoyd

"Lloyd E. Sponenburgh" wrote:

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?)G

LLoyd

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?

"Pete C." fired this volley in news:4fc5805c$0$2982
:

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?


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

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...

(better'n Car Talk, huh?)G

Does your brother build machines better than you do?

"Bob La Londe" fired this volley in news:1_gxr.16557
:

Does your brother build machines better than you do?

Don't build machines like my brother!

Lloyd

On Tue, 29 May 2012 21:21:34 -0500, Lloyd E. Sponenburgh wrote:

"Pete C." fired this volley in
news:4fc5805c$0$2982 :

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?


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

Is it rated for flow?

Weird. Or stupid. Or something.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

Tim Wescott fired this volley in news:Hd2dndYNYZ_
:

Is it rated for flow?

Weird. Or stupid. Or something.

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! G

LLoyd

On Wed, 30 May 2012 11:33:04 -0500, Lloyd E. Sponenburgh wrote:

Tim Wescott fired this volley in news:Hd2dndYNYZ_
:

Is it rated for flow?

Weird. Or stupid. Or something.

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! G

And Not A Moment Too Soon.

--Winston