Page 225 - Reciprocating Compressors Operation Maintenance

2 1 O Reciprocating Compressors: Operation and Maintenance

AVOIDANCE OF OVERCOOLING—AN IMPORTANT ISSUE

While low gas temperature is usually beneficial, cooling should be con-
trolled to avoid harmful condensation of vapor that is always present in air
and in many gases. This is important and must be emphasized, as it is often
overlooked. Condensation can impair lubrication or cause formation of rust
in the cylinder bore. This condition can accelerate wear of the cylinder and
piston and, in non-lubricated units, Teflon rings and wearing bands.
Condensation in cylinders can usually be prevented by regulating the
cooling water rate to control the water outlet temperature. The correct
water outlet temperature is a function of inlet gas temperature, moisture
content, and discharge pressure. No one value is best for all conditions.
An outlet water temperature of approximately 100°F to 130°F is a good
average figure for many installations.
Unduly low jacket cylinder cooling water temperatures will result in
the following difficulties:

1. Piston ring wear
2. Cylinder bore wear
3. Wear of valve seats
4. Valve sealing element wear and breakage
5. Packing wear and leakage
6. Piston rod wear

CYLINDER COOLING SYSTEMS

Series and Parallel Systems

Coolers and cylinders may be arranged for series or parallel flow.

Series Flow

In series flow, the water passes through the intercooler or aftercooler
first and then through the cylinders. One of the two coolers, but not the
jacket, should receive the coldest water. In the intercooler, this results in
the greatest power savings. In the aftercooler, it permits the greatest
moisture removal.
Usually, there is no harm in cooling air to as low a temperature as pos-
sible in the coolers. However, with some gases, it is necessary to limit the