This is a engine/pressure issue?

Question

OK not sure where to ask this hopefully someone knows.

If I have a air canaster presurized with 30 psi on the inflow side of the air conpressing engine and on the outflow side I had a canaster that could hold up to 40 psi on the other..... Nowthe real issue is this lest say the aircompressing motor could only compress to 10psi would it be able to fill the 40 psi tank or would you need a 40 PSI compressor?

I know nothing of engineering but wondered if 30 psi inflow plus the 10 its able to compress might allow the smaller motor to work???

Im think im not seeing the forest for the trees here could someone tell me if it might or might not work and WHY?

Anonymous · Accepted Answer

I think I can see what you're getting at - you're thinking that if the air pressure has already been raised above atmospheric before entering the compressor cylinder will a lower powered compressor be able raise it to the pressure you want. 
Mechanically speaking It depends on the design of the compressor & some may be able to do as you suggest if the air entering the compressor is able to act on the underside of the piston (if it is a piston compressor) throughout it's stroke. That way the effective load on the compressor would be the differential between the underside & the top on the piston. Some compressors may allow this but by no means all of them. Generally what you're suggesting would overload a compressor that was only designed to pump to 10 psi & the pressure at the beginning of it's stroke would be very high in comparison to what it was designed for. 
From a fluid mechanics point of view these things get a bit involved as no gas will compress adiabatically since heat is given off when it's compressed & absorbed when it expands. That means that when you've compressed a given volume of a gas & some of it's heat is given off it will not expand back to it's original volume until it absorbs the same amount of heat it gave off. But to cut a long story short you're compressor is increasing the pressure of the air it sucks from the atmosphere by about 2/3 of an atmosphere. If it were to take in air at 30 psi & increase it to 40psi it would be increasing it by about 30% of it's original pressure. It probably stands a reasonable chance of doing it. 
As I've said above the limiting factor would be the mechanical load on the compressor which I don't think would be up to the job.

Anonymous · Answer

interesting!

seems it might work. the compressor is taking air at some pressure and compressing it further.

On the other hand the compressor only has enough force to move the piston against 10 psi no matter what p was used when the intake valve was open. Filling it with 30 would stall the motor just as if it had started with 1 atmosphere and tried to compress it past 10

I think it depends on the design of the compressor. Is the back of the piston at 1 atmosphere or at the same as the intake p?

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This is a engine/pressure issue?

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