Page 413 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 7 .12
Be st Practice 7 .13 Lube, Seal and Control Oil System Best Practices

r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Therefore, the maximum pressure at 1000 SSU will be 262
viscosity
4
overpressure @viscosity ¼ overpressure @500 SSU psi, or 19%.
500 SSU
Relief valve overpressure expressed as a percentage of relief-
r ffiffiffiffiffiffiffiffiffiffiffi
1000 valve set point is defined as accumulation. Typical values of ac-
4
¼ 35 psi
500 cumulation vary between 10 and 20%.
¼ 35 psi 1:19
¼ 42 psi

Best Practice 7.12Practice 7.12
Best
Install sight glasses in the drain lines of positive displace- required start of the auxiliary pump which did not occur in
ment pump relief valves to confirm that the relief valve is time to prevent a low oil pressure trip.
not passing. Feeling the discharge line of the relief valve gives a false impression
It is very difficult to confirm that a positive displacement pump relief of valve condition, since most oil system relief valves are the modu-
valve is not passing. lating type with a small bypass hole to prevent sticking of the valve that
A friction-bound relief valve can cause an unexpected shutdown of allows a small continuous of flow to pass through the valve.
an oil system by passing an amount of additional oil flow that can force Therefore, the use of sight glasses in relief valve discharge lines of
the start-up of an auxiliary pump, thus exposing the unit to a shutdown the proper pressure is the most effective way to confirm the proper
if the auxiliary pump does not start in time. operation of relief valves.
Requiring all pump relief valve discharge lines to be supplied with
a sight glass of the proper pressure rating will enable personnel to Benchmarks
monitor the condition of the relief valve, and so be able to take ap- This best practice has been used since 1990, when a project with
propriate action when necessary. a Europe-based compressor vendor used relief valve sight glasses as
a standard scope of supply. This practice has saved many un-
Lessons Learned necessary unit shutdowns for critical equipment trains and has opti-
Critical (un-spared) unit trips have been caused by friction- mized train reliability (99.7% or greater).
bound relief valves being stuck open, resulting in a

B.P. 7.12. Supporting Material

Please refer to material in B.P: 7.11.

Best Practice 7.13

Use oil-actuated control valves with a sensing line anti- Lessons Learned
pulsation device whenever possible in oil systems, for End users have found, after many oil system trip events,
rapid transient response and stability. that the use of oil-actuated control valves to replace
Oil systems can use oil or pneumatically actuated control valves. pneumatically actuated valves ensures optimum oil system
It has been my experience that pneumatically actuated control and serviced unit reliability.
valves require more corrective adjustment than oil-actuated valves,
and they do not respond at the required speed during most oil system Benchmarks
transient events (main oil pump trip, auxiliary pump start, etc.). This best practice has been used since the early 1970s, when I was an
Oil-actuated valves can always be used for the backpressure
(bypass) valve, lube oil supply valve, control oil supply valve and seal oil oil system designer for a compressor/steam turbine vendor. Many field
installed systems with pneumatic actuated control valves have been
differential pressure control valve. replaced with oil actuated valves, resulting in trouble-free system
Oil-actuated valves should be supplied with an oil sensing line anti-
pulsation device to ensure stability during transient events. operation and optimum unit reliabilities (99.7% or greater).

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