If the pressure is allowed to build in the exhaust, this reduces the effectiveness of the power stroke, but where the reduced pressure can be used immediately this does appear logical.

Would it not make more sense in most applications to take the exhaust air for re-pressurisation, in the same way that hydraulic units are operated? Even if the pressure has to be reduced on the way, there is still the benefit of the air already being clean and dry.

Hi GM1964

The exhaust pressure would be a problem if uncontrolled. For items dependent on the lower pressure a make up regulator should be teed in to the low pressure (exhaust) manifold and a relief valve into a coalescing muffler or as you suggest back to the compressor intake.

A large percentage of the pneumatic cylinders in operation have speed control valves or restricted exhaust to control their speed. The net result is that during the work stroke only a part of the potential pressure differential is used. Restricting the exhaust results in opposing pressure on the exhausting side of the piston like a tire pump. In many cases 30 psig or ??? back pressure in an exhaust manifold would produce a similar result. The speed control valves could still be used but with less restriction. For those cases where every bit of energy and speed is required the exhaust connection can be omitted.

My guess is that in many cases 10% or more of the energy used to compress the air could be saved. If the compressor is driven by a 50 HP motor would it be safe to say this might save 5 HP at about $2 - $3 each eight hours?

Using the output from one component to directly drive another would also mean that a defect - or re-tool shutdown - in one could cause the other to stop.

I'm sure that the savings are there to be made, but the effort to design & fit return pipes, regulators, etc would mean that returns would be slow in coming - unless a new generation of equipment was designed with the return system in place (twin wall hoses?)

This would have the benefit of a degree of suction from the pump, and the possibility of reducing noise levels caused by vibrating air. (In case you have not guessed by now, my experience is limited to air tools)

Hi GM1964

Yes indeed. Air tools, air motors, would be a category of devices that would be hard to incorporate into a low pressure exhaust system. All back pressure on the tool would be reducing torque.

Since you obviously have an inquiring mind think of how this might work with items other than air motors, tools.

This is obviously so far from my field...I can't think of what sort of power sources you mean. Are we talking exhaust gases from engines? Or reclaiming the compressed air exhausted from commercial vehicle brakes?

I think the subject is pneumatic actuators on production lines, where a single supply is used to feed many devices, some of which require much less pressure than others, and could therefore be run from the "used" air from another device, rather than constricting their supply or fitting springs/dampers to regulate the speed.

The forward pressure of a press would remain the same, but the unloaded return would be damped by the back-pressure in the "exhaust" hose.

Ah! Ta - I think!

Yes!, but as others say, we need someone to make the 'tools' and associated hoses and accessories first.

It is well within the wit of engineers to design things to give ADDED VALUE to exploit the idea, but unfortunately once the accountants and lawyers get hold of it, they simply create ADDED COST to kill it stone dead.

Good luck!

Hi Horace40

I was actually thinking of separate plumbing for the high pressure and the low pressure (recycled exhaust). Parallel pipes should not be difficult. They could be color coded or have visible gauges to differentiate them.

An additional benefit would be a pristine work environment with all exhaust piped away.

"RECYCLE EXHAUST AIR Sept. 27, 2005 --- Recycled May 2007"

This comes under the heading of "It All Depends."

Do you have a work area where it is feasible or scattered small applications? The first should be analyzed in detail, the latter could be dismissed as either to expensive to implement and/or too small to consider.

Hi Stirling Stan Sir (SSS)

At some point and now would work for me architects and mechanical contractors could start installing duplicate parallel plumbing systems for compressed air in new facilities. One of these systems would be for conventional "Shop Air" and this air would serve many devices and applications in the usual manner. The exhaust flow from some of the valves could be connected to the second plumbing loop with the proper contingencies provided.

Enlightened manufacturing engineers and maintenance people could then decide when, if and how they might utilize a new opportunity and ingenuity.

It would be somewhat difficult to retrofit a captured exhaust system piece meal. It might require a commitment to install a complete second system and then teach a better way.

Same old, same old, force of habit pneumatic systems are not a study in creativity.

What ever happened to that high speed motor cycle engine that had large oval shaped pistons. It looked to me like it could have been made into one heck of a compressor.