Page 150 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 3 .4 Compressor Best Practices
Reciprocating compressor cylinder valves

There are many different types of reciprocating compressor
valves. Regardless of their design, all valves perform the
same function, in that they allow gas to enter the cylinder,
prevent recirculation flow back to the suction piping and
allow gas to pass into the discharge system when the process
discharge pressure at the compressor flange is exceeded.
Valves are the highest maintenance item in reciprocating
compressors. Their life is dependent on gas composition and
condition, gas temperature and piston speed. Typical valve
lives are:

- Process gas service in excess of one (1) year
- H 2 (hydrogen) gas service e 8-12 months
In hydrogen service, particular attention should be paid to
cylinder discharge temperature in order to obtain maximum valve
life. Cylinder discharge temperature for service with > 60%

H 2 should be limited to 250 F. Recently, light weight, non me-
tallic valves (made from PEEK) have been used successfully to
increase the valve life in H 2 service to above one (1) year.
Figure 3.4.8 shows a typical channel valve assembly.
The life of the channel valves shown is controlled by the
spring force of the valve springs. The channel arrangement re-
Fig 3.4.9 HDS suction and discharge valves (Courtesy of Dresser Rand)
duces the forces on the valve seal and usually results in increased
valve life.
Figure 3.4.9 depicts a ring or plate valve assembly. This type
of valve is most widely used. Piston assembly
Regardless of the type of valve, condition monitoring of valves
is important to the profitability of any operation. The following Figure 3.4.10 presents a typical piston assembly consisting of the
parameters should be monitored: piston rod nut, piston rod, piston and piston nut.
Piston rod materials are hardened steel and can include metal
Type of valve spray in packing areas to extend rod life. Piston materials can be
steel, cast nodular iron or aluminum. The most common is cast
Suction - Valve body temperature
- Compressor volume flow rate iron due to its durability. Aluminum pistons are used in large
Discharge - Interstage process gas temperature cylinder applications (usually first stage) to minimize piston rod
- Compressor volume flow rate assembly weight.
Figure 3.4.11 shows piston rider bands (2) (items 111) and
Changes in these parameters in excess of 10% from original piston rings (3) (items 113).
(baseline) values should be cause for component inspection and The rider band and ring material is dependent on cylinder
replacement. lubrication. If the cylinder is lubricated, carbon materials or

Fig 3.4.10 Rod and piston

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