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The Practical Pumping Handbook ...........

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Recirculation Line By-Pass -~
Valve i

Figure 10.8: Recirculation pipe diagram

some kind of isolating valve. As the check valve protects the pump from
being driven backwards by returning fluid when the pump is shut
down, it should be located closest to the pump discharge vane. In
addition to isolating the pump for maintenance, the isolating vane may
be opened slowly when the pump is started up on an open system, and
thus prevent the pump from running too far out on the pump
performance curve while the system is being filled. Both discharge
valves should be located in the system downstream from the concentric
pipe increaser to prevent unnecessary turbulence at the valve.

A By-Pass Valve may be necessary to regulate the discharge flow if
prolonged periods of low flow operation arc expected due to variable
system demand. It may also prevent an excessive number of pump stops
and starts which is particularly important with larger motor drivers.
As shown in Figure 10.8, the recirculated flow should direct excess flow
back to the suction source of the pump. It must not be directed back to
the suction of the pump where excessive line turbulence may result.

10.3 Alignment

Industry has progressed well beyond any discussion of the statement
that good alignment is essential to safe and trouble-free operation of
rotating equipment. The only questions that still remain in some areas
are; 'what is alignment?', and, 'what is good alignment?'.
When we discuss 'Alignment' in the pump industry, we are discussing
either 'Piping Alignment' (which we reviewed in Chapter 10.2.1.6) or
'Shaft Alignment'. It must be noted that the term 'Coupling

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