"Ned Simmons" wrote in message
...

On Wed, 19 May 2021 12:43:21 -0400, "Jim Wilkins"
wrote:

Ned Simmons" wrote in message
.. .

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:



The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

Look at "sequence valves."

For example:
http://valveproducts.net/pressure-se...sequence-valve


Rich Smith

--
Ned Simmons
---------------------------

You need some bistable hydraulic, mechanical or electrical memory device
that remembers if the pressure should be increasing or decreasing after the
limit sensors stop signaling the limit condition, and operates the valves
accordingly, and that sequence valve could be the trigger that switches it
at the high pressure side.

The proper sequence valve may do it all. See Figure 2 on the page I
pointed to. Connect the IN port to a tee at the cylinder's port; the
OUT port resturns to tank. It'll act like a relief valve when the
pressure reaches the preset, but unlike a normal relief, won't reclose
until the pressure drops to a very low value.

--
Ned Simmons
-----------------------------------

I'll take your expert word for it. My brain is still in a primitive BC
state. (Before Coffee)
https://www.hydraulicspneumatics.com...equence-valves

"When flow stops, spring force closes the main poppet because pressure has
equalized."