Page 50 - Reciprocating Compressors Operation Maintenance

Reciprocating Compressors and Their Applications 37

3. Less maintenance.
4. Ability to increase use of air without immediately increasing plant size.

Load factor is particularly important with air-cooled machines where
sustained full-load operation results in an early build-up of deposit on
valves and other parts, thereby adding to maintenance. Intermittent oper-
ation is always recommended for these units; the degree depends upon
the size and operating pressure. Air-cooled units for higher than 200 psig
pressure are usually rated by a rule that states that "pump-up" (compress-
ing) time shall not ordinarily exceed 30 minutes, nor be less than 10 min-
utes. Shutdown or unloaded time should be at least equal to compression
time. This means 50% load factor.

Mtiltistaging

Any air-cooled compressor for 80 psig or higher pressure should have
two or more stages of compression, unless it is very small. A two-stage
unit for 100 to 200 psig will run 100° to 150°F cooler than a single-stage
unit, thus reducing deposit formation and the need for cleaning valves.
Two-stage compression of air to 100 psig also saves 10 to 15% in power
over single-stage compression.
Heavy duty water-cooled units for the same service are more economi-
cal to operate than the air-cooled units and normally run at considerably
lower speed and temperatures. Hence, maintenance will consistently be
less. They are universally two-staged for 100 psig air service above
approximately 125 BHP.

Floor Space

Floor space and its shape will, at times, influence selection. The
opportunity for selection will be broadened if the exact dimensions of the
space available are given to all manufacturers. Design adjustments or
alternate arrangements are often available.

Foundation Needs

Foundation requirements for rotating compression machinery will
almost always be less than for an equivalent reciprocating compressor,