Ned Simmons writes:

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I've designed hydraulic systems that included sequence valves, but I
wouldn't want to make a prediction on how repeatable the cracking
pressure might be, especially at high cycle rates relative to the size
of the device. It's also likely to drift with oil temp, though that's
a slow-changing parameter that could be compensated for manually.
Probably best to speak to manufacturers, Eaton/Vickers, for example.

--
Ned Simmons

Ned - that's what I "feared" - it will likely settle down to a stable
pattern, but what that is will drift around in time, with many
variables, including ambient temperature, etc.

Running 24hrs a day for many days, you couldn't keep fine-tuning to
stay on one condition.

I'm seeing why servo-hydraulic with digital logic control on the basis
of pressure transducer(s) is the way things are done.

By the way Ned - "drift" affects welding - not sure how much that is
your thing. "drift" is central to a funny (?) story.

This Company owner knew I wanted to get ahead, so ordered the Foreman
- "Don't let Richard weld - he doesn't know how to". Well, this job
comes in with far thicker plate than anyone has ever met - even the
"old-timers" with 40+ years experience. They couldn't get their welds
to "stick" in those slot-welds. None knew spray-transfer. Co. had
one really good machine, and I flipped it up into spray and was
putting in these slot welds easier than shelling peas. These big
structurals were up on plinths, so I was up there in the middle of the
shop, on top of these things, putting in the welds no-one else could.

No-one came and asked me how I did it.

Reason - they knew I'd say "Don't know. I can't weld. I just pick up
the torch and it seems to work".

The reason they couldn't just copy my setting, or order me go buy
striped paint while they take the torch and continue on that setting
is - conditions drift...
You have to tune and get back to the right condition every few
minutes.
Variables?
Line voltage?
Ambient temperature?
How long since the machine was turned on?
etc.

If you drift downwards, the wire will stub and the weld will
transition to dip transfer. Get too long and it can burn-back to the
torch which will instantly destroy the contactor tip and probably the
shroud. You'll spend a long time rebuilding your torch (N.Am. "gun")
if you don't know how spray works.

So yes, drift...

Again Ned - thanks, appreciated.