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(surftom) wrote in
om:

I'd also like some good links or recomended texts on Hydraulics as I'm
starting to 'play' with them. First project will be a press. I have a
powerpack (AC 5Hp) already but I don't want to 'screw it up'
I have found and understand the basic theories, but could anyone
suggest a good place to get a glossary or explanaition of terms like
spools, 2 3 4 way valves etc.

I understand the Army (US) had a publication, but since most of those
sites were secured last year you cannot download the docs anymore.

Any reference texts (basics) you recommend?

Most of what I know was found in the Hydraulics 101 section of
http://northernhydraulics.sofastweb.net

Sorry Don, can't answer your questions but thought I'd ask on this
thread anyway.

Tom

(don schad) wrote in message
. com...
Hi all.

I am scheming to build a front-end loader for my tractor, and I have
been looking into hydraulics. I have a couple of pretty basic
questions which I have generated after reading various sources and
looking through the catalogs. Any help/insight into any of these
questions would be much appreciated.

First question regards spools for open-center systems. Some Army
literature talks about open-center spools versus tandem-center
spools.
Assuming a 4way with lines T (tank), P (pump), A and B (ports to
cylinder) my understanding is that in neutral an "open center" spool
connects all ports (A,B and P) to the T (tank), such that there
wouldn't be any pressure to the cylinder (i.e. it is floating in
neutral). A tandem open-center spool (in neutral) connects P to T
(so it is just passing through the spool), and closes off A and B,
holding pressure in the A/B loop.

In the first case, a loader w/ an open-center as described would come
crashing down when you let off the controls, whereas the tandem would
hold it's position. Looking at the catalogs I haven't seen a
reference to a "tandem" spool, but I have seen "open-center with load
checks", and further reading suggests that load checks will hold the
cylinder in position.

So, is what I'm calling a tandem spool the same as an "open-center
with load checks"? Does a load check in a spool close off the lines
in neutral?

Second, if you have a spool that is rated for say 25GPM, will there
be any problem running it at a lower GPM? Say 12GPM or 5? Will it
still function properly/safely?

How is pressure controled in the system? Is it just a matter of
setting the relief/bypass values, and the lowest one will control the
pressure (although I guess this would depend on how it was plumbed)?
Most seem to say that they function from 1000psi to 3000psi - does
this mean I can make any combination of pressure/flow rate in the
system to achieive my goals or fit my pump/equipment?

What is the difference between a welded versus a tie rod cylinder?
Pros/cons?

Finally, in parallel spool decks is the flow simply divided between
the open spools, such that everything will work, but at a lower
speed?
And pressure in all A/B lines is the same (so all spools get there
input from the P line)? In series is it that the flow out of one
spool feeds into another spool (so input is from the T line), and we
get a decrease in the pressure (with the same flow)?

Thanks in advance for your help. I appreciate any and all comments
and info.

don

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.

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

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