Unusual pneumatic problem

[swabbie58]

I have a project where compressed air might be useful, but would like to hear from those with more experience. Due to specific limitations, I can't use electricity to power a compressor--but there is the option to use a square chamber into which a bar can be intruded with over 1000 lbs force (probably more). The volume of the chamber is 950 cu.in. and the bar that plunges into it eats up 864 cu.in.--displacing an equivalent amount of air. This air will exit the chamber through a hose of any diameter I wish. What psi can I expect at the end of the hose?

 

[viscomike]

If there is no pressure rise or temperature rise then flow is simply 864 cu.in. per stroke.

Otherwise:

(PxV/T)1 = (PxV/T)2

P = Pressure (absolute pressure, not gauge pressure)
V = Volume
T = Temperature (absolute units - Kelvin or Rankine)

If the temperature stayed constant (it won't, it will rise), and you have a 9 atmospheres flow restrictor at the end of the chamber then approximately you have a 90% decrease in volume and the pressure will increase by 900 per cent.

Flow at this pressure/volume/temperature is dependent on how many strokes per minute.

 

[zdas04]

If I assume that the throw on the rod is 4-inches, then the square hole is almost 15X15 inches (216 in^2). Exerting 1,000 lbf on this area gets less than 5 psi.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

 

[MintJulep]

Pressure will not be greater than 1000 pounds / area of the end of the rod.

At this point, the pressure will balance the insertion force, and the rod won't go in any further.

Depending on the geometry of the chamber and rod, you may or may not reach this limit.