Question: Presuppose that in the calculation example above there is an extra requirement
from consumer 1 of a further 200 l/s for 40 seconds on the hour. It is accepted during this
phase that the pressure in the system drops to 5.5 bar(e). How large should the receiver
volume be to meet this extra requirement?
Answer: It is possible, during a short period, to take out more compressed air than what the
compressor can manage by storing the compressed air in an air receiver. However, this
requires that the compressor has a specific over capacity. The following relation applies for
this:
where
Q = air flow during the emptying phase = 200 l/s
t = length of the emptying phase = 40 seconds
P1 - P2 = permitted pressure drop during the emptying phase = normal pressure in the
system - minimum accepted pressure during the emptying phase = 6.46 - 5.5 = 0.96 bar
Inserted in the formula to give the requisite air receiver volume:
In addition, it is required that the compressor has a specific over capacity, so that it can fill
the air receiver after the emptying phase. The selected compressor has an over capacity of 5
l/s = 18000 litres/hour. As the air receiver is emptied once per hour the compressor’s over
capacity is more than sufficient.
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