4. Now measure dimension “X”, shown in figure 4.4. If
this measurement does not fall within the tolerances
shown in Appendix B, remove the piston head, adjust
the shims as necessary and re-measure the “X”
dimension. When the piston is properly shimmed,
torque the locknut to the value listed in Appendix B.
5. Now install a new lock pin to secure the locknut.
6. Install the piston head and tighten the socket head
bolts in an alternating sequence using the torque
specification in Appendix B.
7. Reinstall the compressor head and follow standard
start-up procedure.
4.5 Piston Rod Packing Adjustment
Piston rod packing should be replaced whenever
leakage approaches an unacceptable level. “Acceptable
leakage” should be determined by the customer
according to safety and environmental regulations for
their area. The upper packing sets are not adjustable.
If the lower packing sets cannot be adjusted to an
“acceptable leakage” rate, all packing sets (upper and
lower) should be replaced. Typically, it is a good idea to
replace piston rod packing and piston rings at the same
time. Instructions for packing replacement are included
with each set of packing.
To adjust the lower packing, remove the compressor
inspection plate (see Figure 4.5A), tighten the packing
adjusting screw(s) 1/4 turn with the wrench supplied,
then run the compressor a few minutes to reseat the
packing. If the leakage is still unacceptable (see Figure
4.5B), tighten the adjusting screw as necessary, 1/4 turn
at a time; do not over tighten! If the adjusting screw is
tightened until the packing spring is solid, the packing
should be replaced. If packing will not seal, carefully
inspect piston rods for possible scoring and replace if
necessary. Reattach the compressor inspection plate
after adjustments or repairs are made.
Figure 4.5A: Typical inspection plate
Also serves as the packing adjustment screw cover.
5. Piston rings and expanders may then be easily
removed and replaced. Corken recommends replacing
expanders whenever rings are replaced. To determine
if rings should be replaced, measure the radial
thickness and compare it to the chart in Appendix B.
Figure 4.3: Piston head removal
4.4 Piston Replacement
WARNING
Before replacing the pistons,
depressurize the
compressor and purge if necessary
.
Remove the compressor head after depressurizing the
compressor (see section 4.2).
1.
To replace the first or second stage piston,
remove the piston head by loosening and removing
the socket head bolts holding the piston head to the
piston platform (see Figure 4.3).
2. Next, remove the lock pin with needle nose pliers. The
locknut may now be removed and the piston platform
lifted off the end of the piston rod. Inspect the shim/
shims for damage and replace if necessary (see piston
assembly details in Appendix E).
3. Reinstall the piston platform with the same thickness
of shims as before, BUT DO NOT REINSTALL THE
LOCK PIN. Reinstall the piston with new piston rings
and expanders.
“X” Piston
Clearance
Piston Head
Shims
Roll Pin
Piston
Bolt
Piston Locknut
Piston Ring Expander
Piston Ring
Piston
Platform
Cylinder
Piston Rod
Figure 4.4: 1st and 2nd stage piston.
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