Accumulator Precharge Pressure
Accumulator Precharge Pressure
(OP)
i'm designing a very basic form of a pneumatic system which involves a telescoping cylinder with a pressurized air chamber acting as an accumulator. what i'm having trouble figuring out is how much pressure to charge the accumulator with to extend the cylinder and hold it. i want to keep the pressure to a minimum, just what's required (of course with a safety factor included).
Volume of Extended Cylinder = 12.5 gal
Volume of Accumulator = 12.98 gal
Accumulator fill temp. = 70F
Accumulator operating temp. = -45F
Pressure required to raise cylinder = 12 psig
i've been using the Ideal Gas Law P1V1 = P2V2 and P1/T1 = P2/T2 but am not sure if this is giving me the results i'm looking for. any help would be much appreciated. Thanks
Volume of Extended Cylinder = 12.5 gal
Volume of Accumulator = 12.98 gal
Accumulator fill temp. = 70F
Accumulator operating temp. = -45F
Pressure required to raise cylinder = 12 psig
i've been using the Ideal Gas Law P1V1 = P2V2 and P1/T1 = P2/T2 but am not sure if this is giving me the results i'm looking for. any help would be much appreciated. Thanks





RE: Accumulator Precharge Pressure
You are close applying the gas laws, one more step to get there would be the mass of gas involved. Presuming the the system is sealed, this will not change. Determin the mass of gas present in the volume at the extended state;
m=PV/RT
Use this mass as the basis for determining the pressure at teh smaller volume of the accumulator. The mass must remain constant.
Cheers
Mark Hutton
RE: Accumulator Precharge Pressure
Ted
RE: Accumulator Precharge Pressure
Ted
RE: Accumulator Precharge Pressure
Set up three conditions.
1. Fill the accumulator: P1, V1, T1
V1 = 12.98gal , T1 = 534.69R
2. Cool the system, a constant volume process: P2, V2, T2
V2 = V1; P1 = P2 * T1/T2
T2 = 414.69R
3. Expand the accumulator into the cyclinder, an isentropic process: P3, V3, T3
P2 = P3*(V3/V2)^k , k=1.3
V3 = 25.48gal , P3 = 26.7psia, min.
Solve for P1: P1 = P3*(T1/T2)*(V3/V2)^k = 82.74psia or 68psig.
Ted
RE: Accumulator Precharge Pressure