Page 226 - Reciprocating Compressors Operation Maintenance

Operation and Maintenance of Reciprocating Compressors 211

cooling in order to avoid condensing the gas or one of its constituents in
the intercooler.
In multistage compressors, the possibility of moisture condensation in
the cylinder is greater at high pressures than at low pressures. Therefore,
in a two-stage unit, the water should flow through the low-pressure cylin-
der jacket first, then through the high-pressure cylinder jacket.
One benefit of series flow is that it requires less water than parallel
flow. Also, if the water source is cold, the temperature rises as the water
first passes through the cooler. This is beneficial in avoiding over cooling
of the cylinders.
Often the water requirement of the cylinders is less than that of the
cooler. It may then be advantageous to divide the water flow leaving the
cooler, directing one part through the cylinders and the remaining portion
through a bypass around the cylinders. The temperature of the water
leaving the cooler can be controlled by a thermostat in the bypass line.
Similarly, a thermostat in the water line leaving the cylinders could be
used to control the temperature of water leaving the cylinder.

Parallel Flow

Parallel flow is preferred in cases of warm water, or low water pressure,
or both. With warm water (approximately 95°F and higher), there is little
danger of causing condensation, and the problem is to achieve effective
cooling, assuming sufficient water is available. Cylinder cooling is
improved slightly because the water is not preheated in the cooler. Also,
due to lower pressure drop in parallel circuits, higher flow rates are possi-
ble. Higher flow rates may be needed with warm water. Lack of water
pressure differential available to the compressor frequently necessitates
parallel flow. This may be due to low inlet pressure or high back pressure.
All components should be considered when estimating water pressure
drop in a compressor system. This includes not only coolers, cylinders,
and piping, but also automatic valves, thermostatic control valves, hand
control valves, and sight flow indicators. Although sometimes over-
looked, accessories often constitute a large part of the total pressure drop.

Open Water Systems

While its use in new installations is declining, open raw water systems
are still in wide use today. Usually, a city water supply, river, pond, lake,