What is a Hydraulic Air Pump

What is to be gained. Power to produce these pressures with oil, out weight the benefit.

The only way I can think of that this would be beneficial is on equipment where you have available surplus hydraulic capacity and need compressed air. I have seen an air driven reciprocating piston hydraulic pump on equipment that had available compressed air. The hydraulic system was retrofitted to allow more precise and stiffer positioning of a particular part.

As to retaining the heat concentrated by compression, I suppose you could recover or use that, but it would be quickly lost to conduction through the walls of the tank,tubing and so on if it were not used as quickly as it is generated.

I wouldn't say that using hydraulic power to compress air would never be useful but I haven't seen or thought of the case where it is.

theres pumps just the opposite, air/hydraulic pumps for port-a-power units.

I was in a cheese plant where most of the process equipment was powered hydraulic, I could not figure out why......don't know about the air compressors.

Your responses are good. Let's say that the kinetic energy already exists to tap into. From a big flywheel with continuous power supplied to it, or a truck or train or whatever, something heavy is already moving and turning a shaft. Sure you could generate electricity to charge batteries to run electric motors to drive a compressor. You could run compressors direct off belts or gears but you'd need a flywheel, I think. But the electricity isn't what's available and there's no room for compressors with big flywheels.

Let's say that instead, you use a shaft that is already turning and has lots of available power to pump hydraulic fluid to say 3000 psi. Am I correct that this is ordinary everyday pressures in the hydraulics world? Now there are a number of small pumps that were referred to as "hydraulic air pumps". This has already been done, but my friend who told me about it has been gone a long time so I can't ask him.

I believe it was a piston pump. So my question is, as long as it's built well enough, is there any reason why a continuous source of 3000 psi oil on a hydraulic piston can't raise the pressure in a direct drive (like linear common shaft) air piston. In one stroke vs. the usual 3 or 4 stages to reach this pressure. He also mentioned worm gearing so the shaft might have been turning fast but running the pump slow.

As for the question about the heat being lost once it's trapped in the tank, assume that air is leaving the tank as fast as it's going in, so let's say the tank is a more or less constant 2000 psi. As the air leaves the tank, the tank tries to get cold, and as air enters the tank, hot air cancels out the expansion and the tank ends up hovering around ambient temperatures so dissipation throught the walls isn't that fast. The tank was insulated, lined with cork.

Luther

"From a big flywheel with continuous power supplied to it"

If you have, "continuous power supplied to it" why do you need the big flywheel?

The flywheel stores power, you don't need it, you already have "continuous power".

I must be missing something.

A shaft has continuous power, more than needed to do the work but not a hundred times more. Maybe two or three times more than what's needed.

If you direct drive piston compressors from the shaft, the pulsatory nature of compressing air from 0 to ? psi will disturb the smoothness of the source that's delivering the power. That's why I said the compressor would need a big flywheel.

What you're missing is my question. Assuming that heat, sealing, strength etc is handled, is there any reason why a continuous hydraulic push can't direct drive an air piston that's taking in atmosphere, and push it into a 2000 psi tank?

The reason I ask is that this is never done with normal compressors that use crankshafts, bearings, and piston rods. Obviously even if the compressor could take the heat of compressing air from 0-2000 psi in one stroke, the bearings and rods could not. It seems like a hydraulic piston could do this because it would replace the crankshaft, bearings, and piston rods of a normal compressor.

Luther

I think what you're missing is my answer. Once you pay the price of the combined inefficiencies of the systems, what will you do with this compressed air at 2,000PSI?

You can't ignore the "heat, sealing, strength, etc" either, it doesn't work that way.

I'm talking about something that has already been done, not trying to justify that it is the most efficient way. I'm trying to guess or figure out what my friend meant when he said "hydraulic air pumps".

I'm ignoring "heat, sealing, strength" for a period of time until I get one question answered. If it's not possible to push air into a 2000 psi tank with one stroke of a hydraulic piston, then I'm on the wrong path and don't need to waste time answering questions about something that can't work anyway.

If I can find anyone to answer one question, then I can tackle all the problems one at a time.

I'm looking for someone who knows what a hydraulic air pump is because this was in the 1970s and maybe they aren't being made anymore, or maybe they were imported or whatever.

Luther

I think your friend was talking about a hydraulic pump that was operated by air. Air is the driving force not hydraulic. Do not even try to reinvent the air compressor. It will not work the way your are talking, four stage compressors do not have a long live with a output of 2000 psig.

Thanks for your response.

My friend was talking about a hydraulic air compressor, not a pneumatically driven hydraulic pump. It was turned by a shaft as stated above. He sent me some information and it's in black and white, "hydraulic air compressor", but no further description. He has been dead for 21 years and we didn't finish the conversations we were having.

If four stage compressors have a short life doing what they're supposed to do then re-inventing the compressor sounds like just what the doctor ordered!

I can't make a decision based on skepticism alone, this was a real machine, so I'm still waiting for someone who knows what kind of hardware this might have been and what kind of pressure it might have been putting out. I guess there's something called a diaphragm pump but I think this was piston.

Luther