Force, Area, Pressure Question: Positive Displacement Pump
Force, Area, Pressure Question: Positive Displacement Pump
(OP)
I have an exercise I'm working on and had a question wiht regards to P = F/A. If I have a pump used to compress oxygen in order to increase pressure to an external cylinder, which surfaces would incur force as the piston in the pump compresses the gas?
Within the chamber holding the gas (there would be a tube/cylinder wall) and a piston within being pulled back to compress the gas. Would the force to be overcome (which needs to overcome the pressure in the cavity as the piston moves back) be only on the surfaces (area) in which the piston is moving (in that specific direction) or does the pressure on any opposite walls help cancel the forces seen in the direction of movement and this should be taken into account.
Any insights would be appreciated. Thanks.
Within the chamber holding the gas (there would be a tube/cylinder wall) and a piston within being pulled back to compress the gas. Would the force to be overcome (which needs to overcome the pressure in the cavity as the piston moves back) be only on the surfaces (area) in which the piston is moving (in that specific direction) or does the pressure on any opposite walls help cancel the forces seen in the direction of movement and this should be taken into account.
Any insights would be appreciated. Thanks.





RE: Force, Area, Pressure Question: Positive Displacement Pump
Ted
RE: Force, Area, Pressure Question: Positive Displacement Pump
So, just to clarify, the force needed to be overcome the pressure would be related only to the area of the walls inside the cylinder in the direction of the movement.
The attached graphic will give a better idea of the exercise. So the surfaces outlined in green will be the only areas (A) of concern needing to overcome the pressure using P = F/A and pressures on other surfaces do not play a part in determining the force (F) to move the piston?
Thanks again. Just want to be clear on this.
RE: Force, Area, Pressure Question: Positive Displacement Pump
If you want to prove this out do a free body diagram of the piston assembly. For each axial surface, determine the pressure acting on that surface and the area it acts upon. Sum it all up being careful of your sign convention.
Johnny Pellin
RE: Force, Area, Pressure Question: Positive Displacement Pump
Ted
RE: Force, Area, Pressure Question: Positive Displacement Pump
RE: Force, Area, Pressure Question: Positive Displacement Pump
Ted
RE: Force, Area, Pressure Question: Positive Displacement Pump
Ted