Pneumatic accumulator

nanju:

It might help to know the maximum flow rate into the accumulator before you design the 1/4" neck of the accumulator to get good efficiency from it. After you have that number, calculating the size will also be simple.

Mark

Hi Nanju

Last time I looked 1 kg/cm² = 14.28 PSI.

Your range of 5 to 7 kg/cm² = 71.4 to 99.96 PSIG. One accumulator (volume) can hold enough volume to give a 5 sec. decay period with your 1/4 Dia outlet tube at one of these pressures only. When you change the pressure you change the decay time.

It is easy to determine the decay rate of compressed air from a given volume with a spread sheet but the discharge rate (coefficient of discharge) of your outlet tube can vary significantly from a theoretical .25 Dia. orifice.

If you have an adjustable pressure switch you could use one volume and set the drop out pressure at different set points for different accumulator pressures.

The mid range of your pressure span, approximately 6 kg/cm² (85 PSIG + 14.7PSIA = 99.7 PSIA) would come close to a 5 second decay time (Barring any unusual Coefficient of Discharge from your 1/4" Dia outlet tube) with .6 cubic feet of volume. The time would be longer at 100 (99.96) PSIG and less at 70 (71.4) PSIG.

A Rube Goldberg trick would be to start with an accumulator slightly oversized. Pour liquid into the accumulator until your decay time is satisfactory. Dump out and measure the amount of liquid. Subtract that volume from the accumulator size.

For example: Start with an accumulator with 1 ft³ internal volume. Assuming we want about .6 cubic feet the time will be too long. Add 3.5 cubic feet of liquid and test again. When just right subtract the liquid volume from 1 cubic foot and you have a very close size for that pressure.

TM