Page 279 - Reciprocating Compressors Operation Maintenance

264 Reciprocating Compressors: Operation and Maintenance

Cylinders crack for various reasons, and overheating or freezing are
among the most common. If a machine is inadvertently started with no
cooling water flow, do not apply the cooling water with the machine run-
ning. Shut the machine down and let it cool gradually, without water flow,
After it has sufficiently cooled, it may be restarted with the water circulat-
ing. If shut down in time, the worst that usually happens is scoring of the
piston and cylinders. If cold water is applied too soon, the casting will
crack, A high temperature discharge switch may prevent this damage.
In the case of freezing, the protective measures are obvious. Cooling
water should never be left in cylinders that are not in service in subfreez-
ing temperatures. Simply opening drain valves does not guarantee that all
water has been removed. Discharge lines can be plugged. Note, also, that
some cylinders have several drain lines for each head and the cylinder,

Metal Spray

Worn or scuffed cylinder bores on compressors on low pressure air
service may be restored to original size by building up the bore with
metal spray. The cylinder must first be prepared by boring and undercut-
ting, degreasing, and spraying. As much as %>" on the diameter has been
replaced in this manner.

Inspection of Valve Seats

At the time of inspection and taking measurements of the cylinder
bore, an in-depth visual inspection should be done of all the valve seats,
paying particular attention to the condition of the gasket seating area.
Valve seats become damaged by not properly torquing the valve jam
screws or other devices that hold the valves in position. If the jam screw
is not torqued to a high enough value, the valve may become loose dur-
ing operation and "pound" the seat, or if over-torqued, distortion or
cracking of the seat may occur.
Valve seat damage may occur also when the valve seat gasket is not in
the proper position to seal, and wire drawing might then take place. A
folded or wedged gasket can cause indentations in the seating surface.
Many so-called valve problems are not due to bad valves, but rather to
bad valve seat gaskets or valve seats in such poor condition that seating
cannot take place and leakage occurs. In this situation, it is common to