Page 127 - Reciprocating Compressors Operation Maintenance

1 1 4 Reciprocating Compressors: Operation and Maintenance

Excessive oil volumes can cause fouling of valves, gumming of the
packing, and accumulation in the downstream piping system. Because of
the higher pressures and low flow rates involved, a "pressured header"-
type system, similar to the frame lubrication system, is neither workable
nor acceptable.
These systems are "positive displacement" systems that must be capa-
ble of accurately delivering, monitoring, and protecting the oil flow to
each of the required lubrication points.
The force-feed lubrication system used for cylinder lubrication could
well be the most important support system used on reciprocating com-
pressors today. Should it fail or not work properly, the compressor units
could be seriously damaged in a short time of operation.
Ironically, because of its apparent complexity, the lube system is in
many cases the most misunderstood, ignored, neglected, and misused
system on the compressor.

Method of Application

Oil is fed directly to the cylinder walls at one or more points by means
of a mechanical force-feed lubricator or a centralized lubricator system.
The oldest and most basic lube system is the box lubricator, Here, an
individual pump feeds each point, each with an adjustable stroke and
some sight glass to view the adjusted feed rate. The suction stroke of the
pump pulls oil from the reservoir and discharges it down the line.
Box lubricators are driven either from the crankshaft, another moving
part of the machine, or by a separate electric motor. They contain a reser-
voir for oil and individual pumping elements. A camshaft operates the
pumping elements.
There are two types of pumping elements used in the box type lubrica-
tor system: pumps with sight glass (Figure 3-3), and pumps with pressur-
ized supplies (Figure 3-4).

Pumps With Sight Glass

Rotation of the lubricator cam actuates the pump rocker arm assembly
to operate the pump piston. On the piston downstroke, spring pressure is
exerted on the piston causing it to follow the cam. As it moves down, a
pressure reduction is created between the piston and the check valve and