Elementary hydraulic questions

I don't know if things have changed since the 40s, but the usual pumps and rams are rated for 10,000 psi.

The spreading jaws I'm familiar with are not rated for that much pressure, but some may be.

You can buy 10,000 psi hose and quick connect fittings from Enerpac. The hoses are expensive, the QDs aren't too bad. If you need other fittings, McMaster should have hydraulic fittings rated to match, and they carry generic QDs that are compatible with but less expensive than Enerpac brand fittings.

No, plain iron pipe is not suitable for 10,000 PSI hydraulic use. The normal configuration of these units has a 10,000 PSI WP rates hose coming directly off the hand pump, and they have high pressure rated screw type hydraulic QD couplings for the attachments.

"Pete C." wrote

The quaint little specialty shops in MY kind of shopping mall:

They are behind Fastenal and the electronics surplus store. jsw

Hydraulic pressure in the line is much less than total at the piston. Area of the piston divided by area of the line is the ratio.

hose we used on autos was usually rated at 3-6kpsi and run at

1.8-3kpsi.

Here ya go. Plug in your known numbers:

I can't find burst pressure for black iron pipe or fittings.

-- I merely took the energy it takes to pout and wrote some blues. --Duke Ellington

The hand pumped porta-power and enerpak hydraulic stuff is generally considered 10,000 PSI hydraulics. The hand pumped stuff operates at much higher pressures than most mobile equipment, in part because hand pumped stuff is non-shock hydraulics that doesn't see the pressure spikes common to mobile equipment. The safe operating pressures for small dia

*quality* black pipe are going to be more like 1,500 PSI at best.

I've seen some survive 2000 PSI in hydraulics, and others crack while being assembled. Personally I buy hydraulic fittings that don't look at all like water pipe and store them separately. Reducing bushings that look kinda similar stay on more obvious fittings. The chromate finish is a good indication for new parts but it doesn't survive rough use.

Spare porta power couplers are handy, to patch in a temporary pressure gauge for instance:

's not where I bought mine, just a Google hit, but the price looks good.

jsw

That's not where I bought mine, just a Google hit, but the price looks good.

Most proper hydraulic pipe and fittings is machined from solid bar material, while most water piper fittings are cast. If it looks like it was cast it's pretty safe to assume it doesn't belong in anything but the lowest pressure hydraulic system.

The capacity of spreader jaws has always been significantly lower than a straight cylinder, mainly for keeping that accessory compact, I suspect. The pulling cylinder accessory capacity ratings are typically also lower rated.

The Blackhawks and similar models have been used for generations in autobody collision repair and heavy equipment/industrial maintenance/service areas. The spreader jaws are definitely handy because they're compact, and generally more versatile than prybars or other methods of separating parts.

Spreader jaws' lower capacity is generally acceptable where working space may be very limited.. and will generally cause little collateral damage, unlike much higher capacity jaws-of-life emergency equipment, which typically isn't intended to minimize damage.

Fittings machined from bar stock are the usual construction for the hydraulics and also the mechanical extension tube couplers.

When I got the thing apart, it was evident that the pipe was a kluge to replace an elongated coupler/bushing shown in the patent drawings. I will make a replacement out of honest steel, and it should be good to go. It would seem that the system could be rated for all kinds of power depending on the diameter of the slave cylinder.

Thanks,

Kevin Gallimore

On 1/15/2012 5:06 PM, Larry Jaques wrote: ...

No, the _pressure_ is the same throughout the system--it's the longitudinal _force_ that is proportional to the area perpendicular to the unconstrained dimension.

That's what the link illustrates--the to forces are proportional to their relative areas; the fluid pressure is constant and uniform.

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...the tWo forces...

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