Page 404 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 7.8
Lube, Seal and Control Oil System Best Practices Be st Practice 7.9
subject to wear should be redundant. Critical equipment sys- such that its maximum discharge pressure does not force the
tems incorporate stand-by pumps. Usually, the main and spare centrifugal pump to a low or no flow operating point, when both
pumps are identical in design. This is particularly true if dynamic pumps are operating.
pumps are used, since their performance curves should be The stand-by pump is combined with a control system that
similar to ensure trouble free operation. will automatically start the pump on an abnormal system con-
There are exceptions; some systems use a main, shaft-driven dition (low flow or low pressure). The stand-by pump unit
centrifugal pump and a positive displacement stand-by pump. In (pump, coupling and driver) must be designed for fast, reliable
this case, the positive displacement pump must be controlled start-up and operation on demand.

Best Practice 7.8Practice 7.8
Best

Install differential pressure transmitters to alarm on high caused critical machinery trips when main pump wear
differential, for control room monitoring, around pump caused the auxiliary pump to start too late.
suction strainers e especially screw and gear pumps.
Since only the oil film keeps gear and screw components from Benchmarks
contacting each other, a plugged main pump suction strainer will This best practice has been used since 1990 to ensure that rotary
rapidly increase pump clearance and cause the auxiliary pump to start. pump wear can be prevented, which has resulted in optimum oil
The source of the main pump strainer blockage will eventually plug console reliability and critical machinery train reliability above 99.7%.
the auxiliary strainer and result in auxiliary pump damage.
Lessons Learned
Failure to detect rotary pump (screw or gear) strainer
blockage has resulted in excessive pump wear that has

B.P. 7.8. Supporting Material

This best practice is rarely used by project teams, but can easily adding suction strainer alarms is small compared to the potential
impact critical equipment reliability. The additional cost of reliability reduction and loss of revenue.

Best Practice 7.9Practice 7.9Practice 7.9
Best
Best
Consider motor drives or shaft-driven and not steam tur- Lessons Learned
bine main pump drivers if the electrical system is reliable. Numerous case histories have shown that steam turbine, main pump
Small steam turbine reliability is the lowest of all the lube oil pump drivers have the lowest reliability of any oil pump driver alternative,
driver alternatives. since they cause critical machinery unit trips.
If the electrical system is reliable, dual motor drives operating from
different electrical systems should be a favored alternative or, if the Benchmarks
electrical system is not totally reliable, a shaft-driven main pump is also This best practice has been used for projects and field modifications
a viable alternative. since the mid-1990s to ensure the highest critical machinery reliability.

B.P. 7.9. Supporting Material
Shaft-driven, positive displacement main pump;
Types of lubrication system motor-driven auxiliary pump
Refer to Figure 7.9.1. In this system, a shaft-driven main pump
The classical lube system arrangement consists of a steam tur- is supplied. The function of having a shaft-driven pump is to
bine-driven main pump and motor drive auxiliary pump. In this continuously provide some amount of lubrication to the system
section, we will devote our attention to other system variations. bearings while the critical equipment is in operation. The idea

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