Westinghouse 5026 Instruction Pamphlet page 31

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61
CROSS COMPOUND AlH COMPRESSORS
recommend that the condemning limit should never be
established below 75 per cent, for the steam end of the
tests specified hereinafter, no matter what the service
may be or the apparent ability of the compressor to meet
operating requi "ements, even with a considerably lower
efficiency than this. Where operating conditions demand
a more rigid requirement, the condemning limit should
be raised to an amount determined by the judgment of
those in eharge.
..
The steam end of the compressor should be tested in
the following manner:
The compressor steam throttle should bc opened wide
and the main reservoir pressure should be regulated by
means of a cock or valve leading to the atmosphere until
the pressure in the reservoir reaches 53 pounds. When
this pressure has been obtained, the locomotive boiler
pressure and the compressor speed in single strokes per
minute should be observed and compared with that
shown on the curves, Fig. 24, which represent what the
performance ought to be if its steam end is in good aver­
age condition.
For example, suppose with the steam throttle opened
wide and the main reservoir pressure maintained at 53
pounds, by bleeding it to the atmosphere at a given rate,
observations show that a speed of 100 single strokes per
minute is attained with a boiler pressure of 122 pounds.
The curves show that, if the steam end is in good average
condition, the 8%"-150 compressor operating against a
main reservoir pressure of 53 pounds, with 122 pounds
boiler pressure, should make 104 single strokes per min­
ute, and that the 8V2" -120 compressor operating against
a main reservoir pressure of 100 pounds, with 122 pounds
1{I'~PAll{
SHOP AND ROAD TESTH
boiler pressure, should make 110 single strokes per min­
ute. If the observed speed is less than that indicated on
the curves for the given conditions, the judgment of those
in charge should determine whether the compressor
should be over-hauled.
If the condemning limit for the steam end has been
set at 75 per cent of the performance of a compressor
in good average condition, the speed of the compr.essor
should not be less than 75 per cent of the speed called
for by the curve at a point corresponding to the particu­
lar condition of steam pressure under which the com­
pressor was tested. For instance, in the case under con­
sideration, the compressor should have a speed of not
less than 75 per cent of 104 strokes, or 78 single strokes
per minute.