Variable Volume Clearance Pockets
(VVCP)
A VVCP is used to change the clearance
volume of the head end of a cylinder. The amount of clearance will vary
depending upon the position of the clearance pocket piston. Clearance
is added to the cylinder by turning the piston / stem assembly counter
clockwise (CCW).
Most compressor cylinders can
be equipped with variable volume clearance pockets. The VVCP is mounted
in place of the head end cylinder head. The VVCP includes an adapter,
piston, seal ring, stem, Teflon vee packing, turning handle and locking
wheel.
The expected change in compressor
flow and absorbed power will depend upon the application compression ratio
and the properties of the gas being compressed. Always check to see that
the head end suction volumetric
efficiency or discharge event
are within limit when setting the pocket.
To set the VVCP at the desired
percentage open, fully close the VVCP, and then fully open it, counting
the number of turns to the full open position. Fully close the VVCP. Multiply
the number of turns by the desired percentage open, and turn the VVCP
open the resulting number of turns.
The pocket position can be measured
with a ruler on site. A
pocket position nameplate is attached to newer pockets showing the measurements
for open and closed. This
data can also be found in the Ariel Performance Software.
Refer to the compressor cylinder
DataBook for available VVCP for each cylinder.
Ariel
Corporation Application Manual
27Sept 2005