F
OR
M
ODELS
: JGI, JGM, JGN, JGP
AND
JGQ
S
ECTION
5 - M
AINTENANCE
PAGE 5-45
VVCP - Maintenance
To replace or clean the VVCP packing, mechanically depress the packing assembly spring
and remove the snap ring. A piece of threaded rod, two hex nuts and two heavy washers
may be used to compress the packing assembly. The inner washer must be large enough to
catch the packing assembly, and small enough to allow the snap ring to be compressed and
removed. Use proper snap ring pliers. Replace the VVCP packing when excessive leakage
is noted at the vent. Remove the VVCP piston ring; replace as necessary.
Clean all parts to remove all debris, rust, etc. The stem and piston are permanently attached
to each other, do not attempt to disassemble. When replacing the VVCP packing, place new
packing between two flat surfaces, such as two pieces of wood and tap wood with hammer
to relax the packing elements prior to assembly.
Reassemble the VVCP in reverse order, lubricate and install a new O-ring at the bolt flange
between the two-halves. Refer to Section 1 for bolting tightening torque value. Lubricate
stem with three to four pumps of all-purpose petroleum grease with a hand pump grease
gun at the grease fitting.
To re-install the VVCP on the cylinder, use a new head gasket. Lubricate threads and bolting
seating surfaces with petroleum type lubricant and install bolting. Tighten each cap screw
until snug using a criss-cross pattern. Next tighten each cap screw to 25 percent of full
torque, moving from cap screw to cap screw in a criss-cross pattern. Repeat this step for 50,
75, and 100 percent of full torque. Refer to Section 1 for tightening torque value.
Reconnect VVCP packing vent. Re-install and tighten locking handle (or locknut), install bel-
lows, adjusting handle and Nylon-insert locknut, if applicable. Be sure that thread protector
bellows are properly aligned when installing adjusting handle. Tighten Nylon-insert locknut.
Refer to Section 1 for tightening torque value. When installing a new VVCP, check total pis-
ton end clearance, check crank end/head end feeler gage clearances with VVCP completely
closed. Refer to Section 1 for clearances.
VVCP - Adjustment
VVCP clearance volume may be changed with the compressor running or stopped. Consult
the Packager’s instructions regarding where to set the VVCP. Also refer to the VVCP data
sheet in the Ariel Technical Manual Parts Book.
The VVCP piston ring is designed not to be gas tight, to allow a nearly balanced gas pres-
sure for ease of VVCP adjustment with the cylinder pressurized. Gas pressure behind the
VVCP piston normally vents when cylinder is vented. Process debris or rust around the pis-
ton ring can make a seal that takes some time to vent. If gas is trapped behind the piston,
the VVCP can be adjusted when the cylinder is pressurized, but difficult to turn when cylin-
der is vented. This problem is corrected by disassembling the VVCP and cleaning.
To adjust volume, loosen stem locking handle (or locknut), so that stem is free to turn. Turn
stem by use of adjusting handle on outboard end of shaft (or wrench flats). Turn clockwise to
load; counterclockwise to unload the compressor cylinder. See the VVCP instruction plate
on the equipment for the dimensional positions for fully closed (load) and fully open (unload).
Reference Section 1 for an illustration. Re-tighten stem locking handle (or locknut) to hold
stem in place.
