Low Suction Pressure
At low suction pressures
(below 10 psig) it is difficult for the end user to predict what the actual
supply pressure will be within 1 to 2 psi and/or for the packager to predict
pressure drops within a fraction of a psi. These variations in inlet pressure
and pressure drops can result in a significant change in horsepower and
flow, either upward or downward, depending upon the actual suction pressure.
Ariel recommends that compressor
cylinders in this application be oversized between 5 to 10% and equipped
with variable volume clearance pockets or high clearance valve assemblies
to produce the desired flow. The effect of the actual suction pressure
being 1 to 2 psi higher or lower should be considered when selecting the
driver horsepower rating.
Vacuum Suction Pressure
Vacuum suction pressures can be
applied to Ariel cylinders. The
sensitivity of changes in suction pressure should be reviewed, as in the
above Low Suction Pressure paragraph. Additionally,
the mean cylinder pressure should be maintained above atmospheric pressure.
If the
mean cylinder pressure drops below atmospheric pressure, air can be pulled
into the cylinder and into the gas stream through the packing cases. The
Ariel Performance Program will flag both the suction pressure and discharge
pressure when the net cylinder pressure is less than atmospheric pressure.
Ariel
Corporation Application Manual
21 March 2005