On Wed, 28 Jan 2004 22:32:42 GMT, Anthony
vaguely proposed a theory
.......and in reply I say!:


I suggest the open center valve, since constant flowing fluid requires
less energy than running everything through the pressure relief back to
tank. There will still be some go through the relief, depending on your
pump and the rest of the plumbing.
The open center, to my understanding, will, as you move the spool off-
center, divert flow from the T line to either A or B ports. when the
valve returns to center, all flow goes to T. Remember, unlike pneumatic
systems, you have a constant flow of fluid. It has to flow somewhere. If
it doesn't flow back to the tank through the spool, it will have to go
through the pressure relief, meaning your engine will have to produce
enough power to maintain the max system pressure at all times, not the
best way...you only need pressure when there is work to do.

No kidding there. If you run a hnydraulic FEL, and let it keep pumping
when the ram has reached full stroke, you feel even a quite powerful
machine (120HP) hesitate. I have been caught by the crowd a couple of
times (the lift is a little more obviuos G). A little tractor will
die, at anything other than something approaching full revs, trying to
run the max pressure of a hydro system of any grunt. I learned this
when I took a backhoe off a Massey 40 tractor with FEL/backhoe and
forgot to join the out and in hoses. They have an auto stop on them. I
wanted to move the tractor a few yards, and it just would not run.
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Spike....Spike? Hello?