On another Forum a question was asked about how to evaluate a compressor system and one of the answers included several ways to reduce air consumption. One way noted was this one:

"1 - Is the compressed air system designed for the pressure required by the process? The system may generates more pressure than required to be reduced by a pressure reducing valve in the system. This means you are wasting lot of energy."

Is tis a true statement????????????????

I have only worked on large systems in a mining environment for mobile equipment. A compressor is rated by flow e.g 2600 cubic feet per minute, the pressure is obviously regulated.Air systems are great generators of heat because of the friction between lobes(example only)to pull air through them.The simple movement of air generates heat through friction of the parts.Im not entirely sure this is what you are looking for Bud?

newmanite;

The part I have a problem with is:

"The system may generates more pressure than required to be reduced by a pressure reducing valve in the system. This means you are wasting lot of energy."

Does using a Reducing Valve (Pressure Regulator in Pneumatic Circuits) to reduce High Pressure from the Compressor to a lower pressure WASTE ENERGY?

In other words, My compressor is operating at 120 PSI and at a pneumatically powered machine I use a Regulaator to lower pressure to 65 PSI. The machine operates satisfactorily at that pressure but it also operates satisfactorily at 120 PSI compressor pressure after a few Flow Control adjustments to slow it down.

At the reduced pressure (65 PSI) is the machine using more or less compressor energy?

I believe it is using less energy since the Air (Gas) expands and its volume increases. The added volume moves the actuators at the necessary speed and less energy is used.

Another way of saying it is:

I can pressurize three tires to 80 PSI from an Air Tank filled to 300 PSI but only one tire to 200 PSI. Thes figures may not be mathmatically correct but only to show my way of understanding Gasses.

quote:

Originally posted by Bud T:
"1 - Is the compressed air system designed for the pressure required by the process? The system may generates more pressure than required to be reduced by a pressure reducing valve in the system. This means you are wasting lot of energy."

Is tis a true statement????????????????

It does waste energy. How much depends on the pressure drop just like in hydraulics. If the pump is set to supply 100 psi air then any load will cause the compressor to cycle. If the compressor can recharge its accumulator faster than the load can discharge it the compressor will cycle on and off which is not good.
It may be best to have a little hysteresis where the compressor starts at 90 psi and stops at 100 psi to avoid the compressor cycling problem. If pressure must be maintained at 100 psi then it may be best to charge the accumulator to 120 psi and reduce the pressure. This is similar to what must happen on a servo system. Energy is wasted in return for performance.

Peter wrote:

quote:

It does waste energy. How much depends on the pressure drop just like in hydraulics.

Looks like I have another rewrite in my basic book. I'm beginning to think I have a very poor understanding of Hydraulics and Pneumatics and better leeave it to the experts.

Oh well, I can blame it on senility since turning 75 last December.

I guess those 2,000 PSI botles of breathing air do'nt last any longer than one filled at 200 PSI. What a waste of energy and a Regulator for no good reason.

Same goes for Oxygen and Acetylene containers, just a waste to pump that gas up to those high pressure and waste it all.

And how about pumping Propane Gas up to pressure high enough to turn it into a liquid. What a waste of energy since it does'nt have any more volume when it is used in a gas burner at less than 10 PSI.

Now Liquids at atmospherc pressure is another story.

A container, completely full of water, pressurized to 2,000 PSI has very little energy since it may oly take a few strokes of a Manually Operated pump to reach that pressure. Then when a valve is opened pressure drops when only a few drops of water is allowed to leave the container.

Thats why a well water system for a home uses a tank that is approximately half filled with water and half filled with air. The stored energy in the air can push the water out and the pump does'nt have to run every time a faucet is opened.

Even in hydraulics, an Accumulator uses a Gas to store energy, since Hydraulic Oil, or any other Liquid. has very little compressibility and will not allow energy storage.

Could be wrong though since I get so muddled any more.

Newmanite wrote:

quote:

Air systems are great generators of heat because of the friction between lobes(example only)to pull air through them.The simple movement of air generates heat through friction of the parts.

Book Rewrite coming up again.

Heat in a typical Plant Compressed Air system is from the SQUEEZING the Atmospheric air at approximately 14.5 PSI into roughly 1/8 of its original volume and concentrating the heat into that smaller volume. Needless to say there is some heat due to friction but it is minimal in comparison to the concentration of the heat in the air in th normal plany atmosphere.


The other thing that happens with an Air Compressors Output is it has a lot of water in a liquid form since the amount of vapor in the atmospheric air is also concentrated due to reducing its volume about 8 times so the air comes out HOT and WET on most days in countries with ambient air temperatures well above freezing.

One company puts a Refrigeration type AIr Dryer on a comprssors Air Inlet Flow to cool and condense out the water Vapor. This cooled air is much denser and is rewarmed due to compressing the volume about 8 times.

It's in the book.

Nice Bud, I should have been more exacting with my wording about the friction caused in a pneumatic system.I spoke very loosely in those terms from mow on I shall be more exacting.BTW well done,you are not going senile if this is making you feel better about your understanding of pneumatics,then you are right up there with your explanations

Bud,
Questions you post are thought-provoking and yet very dicey.

In hydraulic systems, pressure reduction would lead to energy wastage for the example quoted.

However even in Pneumatic systems I guess this is energy wastage as HP-output to HP-input ratio is less during 65 PSI conversion.

AKB wrote;

quote:

However even in Pneumatic systems I guess this is energy wastage as HP-output to HP-input ratio is less during 65 PSI conversion.

,

There are some losses since efficiency of any compressor is reduced as pressure increases. However some air users require the higher pressure so one way to conserve air is to reduce the pressure any place possible. AND I DON'T SELL REGULTORS in fact all I sell any more is my Books and my Time.

However, since we are talking about a Compressible Gas instead of Non-compressible Liquid the Volume of the Gas increases as its pressure is reduced, Opposite of What Happens when the Atmospheric Air is Compressed. I can fill several containers with air at a lower pressure from one container at a higher pressure. I can also do the same amount of work longer on a machine powered by air Reduced to 60 PSI in place of supplying the 120 PSI air directly from the compressor.

Both the 60 PSI and the 120 PSI supply will do the work requred but the 60 PSI will do it almost twice as long or at less HP input.

Many would be surprised to know how much compressor HP they are wasting by not operating all Air Powered Devices at the lowest possible pressure that will maintain production cycle.

Even to the point of adding Pressure Regulators at individual actuators on machines that have only one actuator that requires the higher pressure.

I even recommend using 5-Way valves plumbed as Dual Inlets with Working Pressure on the Work Stroke of a cylinder and Reduced Pressure on the Retract Stroke. May not sound like much but the yearly savings in Compressor Energy can be eye opening. Also the need for added compressor capacity might be put on hold if Air Systems were monitored and modified to reduce air cosumption by this and other methods.

When I started working in Fluid Power I learned in one training session that air is not Free as was noted at a lot of auto service atations in the Good Old Days. One thing I learned that has stuck with me since 1959 was "Every Leak You Can Hear Cost's $100.00/Year." A little higher now but you get the point.

A typical hand operated Blow Off Gun requires 3-5 Cmpressor HP and are used by some operators like a Cooling Fan in hot weather. Air Motors use from 7-15 Compressor HP for each 1 HP output. but are often let run continuously while only working a portion of the time.

FREEAIR IS NOT FREE!!!!

This message has been edited. Last edited by: Bud T,

Peter wrote:

quote:

It does waste energy. How much depends on the pressure drop just like in hydraulics.

Do you still brlieve your sttement is true?
If you do can you explain why or how the energy is lost.
Curious in INDIANA.

As a RULE.
If there is a Flow - Q
If there is a pressure Drop - dP
If No Work was Done - W
There is Energy Loss.
No matter if it is Gas or Fluid.

Nahum wrote:

quote:

As a RULE.
If there is a Flow - Q
If there is a pressure Drop - dP
If No Work was Done - W
There is Energy Loss.
No matter if it is Gas or Fluid.

That is true, BUT, it does not apply to the original Post in my opinion.

WORK is being done but at a lower PRESSURE since a REDUCING VALVE allowed the AIR to EXPAND and give more VOLUME that was capable of doing the WORK.

At least it sure proves to WORK in a bunch of applications I have worked with.

but across the pressure reducing valve there is no work done, so the throttling there, pressure drop, is wasted, not?

Kevin weote:

quote:

but across the pressure reducing valve there is no work done, so the throttling there, pressure drop, is wasted, not?

The way I understand it is, an Air Line Regulator is fully open up to or very near its Set Pressure. Then it closes and stops flow that tries to raise pressure at its Outlet.

So, Yes it is a restriction but not like a Flow Control that only restricts flow while Fluid is moving on its Outlet. However, it continues to flow at a reducing rate until the Outlet Pressure reaches In;et Pressure.

That may be Nit-Picking but I know Ross Controls believes in it enough to have a page on it in their catalog:

http://www.rosscontrols.com/energy_saver_valve_from_ROSS_Controls.htm

Take a look at the above page for Ross Controls
valves that tout an air savings of up to 30% while only using reduced pressure on the Retract Stroke.

In fact they are not actually using reduced pressure but are Closing the Inlet to the retract side as soon as the cylinder reaches the retract Limit Switch.

Could be they don't know what they are talking about though???

This message has been edited. Last edited by: Bud T,