5. To ensure the valve gasket is properly seated, insert
the holddown screw and tighten to the value listed
in Appendix B.
WARNING
Gaskets and O-rings are not normally reusable.
6. Replace the O-ring and valve cap (or unloader
assembly if applicable) and tighten to the value
listed in Appendix B.
7. Check bolts and valve holddown screws after first
week of operation. Re-torque if necessary. See
Appendix B for torque values.
4.1.1 Reverse Unloader Option
The reverse unloader option (valve specification 6P)
is recommended when the compressor is required to
start under a load at frequent intervals or in continuous
duty applications. The purpose of a reverse unloader is
to ensure the compressor does not start under a load;
also known as a loadless start or unloaded condition.
To unload a compressor, the reverse unloader holds the
compressor valves open approximately ten seconds
or until the compressor and motor reach a normal
operating RPM. Eliminating the load at startup reduces
the stress on the compressor and motor. To learn more
about the operation and benefits of using unloaders,
refer to pages EE160 and EE161 (latest version) in the
number 5 industrial compressor sales catalog. For part
details, see Appendix E in the back of this manual.
WARNING
The reverse unloader shown below is
pressurized. A pressurized reverse unloader
means the suction valves are closed so the
compressor is in a loaded condition. Conversely, a
depressurized reverse unloader means the suction
valves are held open so the compressor is in an
unloaded condition (see Figure 4.1.1 for details).
4.2 Heads
A compressor cylinder and head very seldom require
replacement if the compressor is properly maintained.
The primary cause of damage to a cylinder or head is
corrosion and the entry of solid debris or liquid into the
compression chamber. Improper storage can also result
in corrosion damage to the cylinder and head (for proper
storage instructions see chapter 5).
Many compressor repair operations require removal
of the cylinder and head. While the compressor is
disassembled, special care should be taken to avoid
damage or corrosion. If the compressor is to be left open
for more than a few hours, bare metal surfaces should be
coated with rust preventative.
When reassembling the compressor, make sure the bolts
are retightened to the torque values listed in Appendix B.
4.3 Piston Rings and Piston Ring
Expanders Replacement
Piston ring life will vary considerably from application to
application. Ring life will improve dramatically at lower
speeds and temperatures.
1. To replace the piston rings, depressurize the
compressor and purge if necessary.
2. Remove the compressor head to gain access to the
compressor cylinder.
3. Loosen the piston head bolts and remove the piston
head as shown in figure 4.3 by pinching two loose
bolts together.
4. Remove lock pin with needle nose pliers. Remove the
locknut and lift the piston platform off the end of the
piston rod. See figure 4.4.
Figure 4.1.1: Reverse unloader assembly for valve specification 6P.
Unloader body
Unloader cap
Unloader spring
Unloader
piston
Pressurized line
connection
Actuator
spring
Unloader
actuator
Valve
assembly
(closed position)
Valve
cage
Valve
holddown
screw
Pressurized
area
14
