# Re: mechanism query

I'm trying to generate 20,000 psi for pressure testing assemblies. Volume
is very small so flowrate is not an issue. I'm trying to design it so that
standard orings and backups can be used to rebuild it. I've pretty much
decided on using 2 - 005 orings with backups for the piston. That size
piston will require just over 250 lbf to generate 20,000 psi. Another goal
is for it to be as simple as possible. I'm considering just pounding it
with a hammer to generate the 250 lbf.

"Kirk Gordon" <kg1@xxxxxxxxxxxxxxx> wrote in message
news:4588B2E8.80909@xxxxxxxxxxxxxxxxxx
dlevy wrote:
I need some suggestions on a mechanism. I'm essentially designing a
piston pump. Maximum required pressure takes too much force.

I need to be able to stroke the pump and then lock in some sort of screw
mechanism to be able to generate enough force to reach max pressure. I
seem to remember something like a nut milled in half but it's not real
clear in my mind. I seem to remember seeing something that was
associated with a mill table clamp set.

Anyone have any suggestions? pictures? funny stories? free money?
tia.

What kind of pressure are you trying to generate?? Piston pumps,
especially with small bores, can develop some monstrous pressures. The
piston can be driven by a crankshaft, which, because of the sinusoidal
action of converting rotary motion to linear, has an effectively infinite
mechanical advantage as it crosses top dead center. Or, you can drive the
pison with a cam to create even more advantage. Or you can simply put the
piston on the end of a screw, and use whatever size or thread pitch it
takes to generate almost any pressure you can imagine.

Multi-stage piston pumps are pretty serious stuff, too. Remember that
the piston mechanism only has to create a difference in pressure between
what comes in and what goes out. For example, if the incomming pressure
is, say, 3,000 PSI, and you want an output pressure of 3,100 PSI, you
don't need a 3,100 PSI pump. You only need a pump that can do 100 PSI
differential between input and output. Of course, it'll have to be
something that won't burst; but the actual pumping part can be fairly
wimpy. Several pumps in series, usually with progressively smaller bores
and volumes, can create any pressure I'd care to get close to.

Hope this helps. Please post more specifics.

KG

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