Air Accumulator Sizing
For critical valves, it is sometimes required to provide an instrument
air accumulator so that in the event of an instrument air failure, the
accumulator enables the valve to still operate correctly a certain number
of cycles (often 3 strokes are required by the customer).
Sizing the accumulator, while at first appearing complicated, is in fact
quite straightforward.
The variables required for the sizing to be carried out are:
- V0:
- The Accumulator volume which we want to
calculate.
- Vact:
- The valve actuator actual volumetric
displacement
- Pact:
- The minimum pressure guaranteed to correctly
stroke the valve fully. Note: This pressure is in absolute units.
- Pair:
- The minimum operating instrument air pressure.
(ie. the pressure below which the air can be considered as having
failed. This is also the pressure at which the accumulator lock-up
system will operate). Note: This pressure is in absolute units.
- N:
- Number of strokes required.
- K:
- A factor depending on the type of actuator, K=1 for spring
return actuators, K=2 for double acting actuators.
The formula giving the correct size, on the assumption that the process
can be considered isothermal, is:
Do not hesitate to email me
for any question about this set-up!
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