On Sat, 04 Aug 2007 09:35:48 -0400, dave
wrote:
I'm sure that you'll get more answerers to your questions then you
expect but I'll lay a little groundwork:


looking to buy a used hyd cylinder on ebay (or some similar source) for
use in a home-brewed tilt trailer. have a couple amateur hydraulic
questions:

if there's no label or tag on a given cylinder, how do you tell by
looking at the cylinder if it's SINGLE acting or DOUBLE acting? also

A double action cylinder will have a hydraulic oil connection to both
ends of the cylinder although as in CAT blade cylinders the
connections will be at the same end but one will have a pipe going to
the other end.

"all other things being equal", how does one tell what weight, say, a
given cylider can LIFT, straight up? for sake of discussion let's assume
load to be lifted has perfect "zero friction" bearings guiding it. I
assume the answer has a lot to do with size of the cylinder *piston*,
and amount of pressure pump puts out "to" the cylinder ? but what's
the formula?

First there are balanced and unbalanced cylinders. The balanced
cylinders have the piston rod extending all the way through the
cylinder.

The formula for a single action cylinder would be Pi X radius squared
of the piston(in inches) X PSI divided by whatever constant you want
to get pounds /Tons/Etc.

For a double action cylinder the formula would be: Pi X radius
squared of the piston O.D.(in inches) minus Pi X radius squared of
the piston rod X hydraulic pressure in PSI divided by any constant you
need to convert to pounds/tons/etc.

There are also double action cylinders that are not balanced so in
that case you use the formula for a single action cylinder on the end
without the shaft and half of the double action formula for the shaft
end.

Usually you also figure in a fudge factor to make sure it really is
big enough like adding 15 - 25% :-)

also, can -ALL- hydraulic cylinders be operated 'in any orientation'?
eg: with cyl body horizontal, vertical, or at any angle anywhere between
the two?

Up, Down, Sideways, don't make any difference.

for application in a tiltbed trailer, I assume a cylinder that's bigger
and with a LONGER stroke mounted, say, closer to the hitch, would be
-vastly- better than having a shorter cylinder with an even bigger bore
mounted closer to the axle (so it had a shorter stroke). that be
correct, then?

Well, space does enter into things a bit. If you want to raise the
front of the body 6 feet in the air and the cylinder is connected to
the front of the dump bed and the trailer hitch it will have to be a
one of those multiple sleeve cylinders like a fork lift uses - which
probably costs a bit.

If you are serious about building a hydraulic dump trailer then go
look at dump trucks and copy the design. They have been b building
them for yonks and pretty well come up with the best ways to do
things.

in same appplication, bubba here also guesses designing a tilt-trailer
to employ very nearly the FULL stroke of the cyl is better that making
it use, say, only half the stroke, correct?

Whether the cylinder is partially full or partially full of oil makes
no difference as the pressure is constant throughout a closed system..
Most designs are sized so at full travel there is some small clearance
between the piston and the end cap.

and is there a way for a guy to some sort of 'intermediate throttle
body' or something so that a single-acting cylinder can be made to
perform 'double-acting functions'?

Not really.

thanks for educating me, guys :-)

toolie

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relies by e-mail, if any, please remove the weirdstuff from my address
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Bruce in Bangkok
(brucepaigeATgmailDOTcom)