Appendix H—Aboveground Installation/Piping Instructions
7
11
12
8
No!
Yes!
No!
Yes!
Yes!
No!
9
10
Since liquefied gases boil when drawn into a pump by its own suction, the pump must be fed by gravity flow to give
stable, trouble-free operation.
Always locate pump below tank level
...the lower the better!
Never locate pump above level
of liquid feeding pump. Product
must be able to flow by
gravity into pump.
Back Check Valve
Positive closure of back check valve
prevents proper vapor return for
pump priming.
Excess Flow Check Valve
Necessary for proper vapor elimination
when using priming type bypass valves.
Always pipe bypass
back to tank! Make
sure bypass line is
large enough to
handle full pump
flow without
excessive pressure build-up.
Note that bypass line must
be capable of bypassing full
pump capacity without
excessive pressure build-up.
High pressure rise can
cause bypass valve to
chatter and vibrate.
Don’t pipe bypass line
back into suction piping!
Heat Building in
recirculated products
causes flashing of liquid to
vapor with immediate cavitation and
ultimate dry-running. This is why the
bypass relief valves which are built
into many positive displacement
pumps should not be used for
normal bypass action when
handling liquefied gases. The internal valve should be considered to be a
back-up safety relief in in addition to a back-up safety relief in addition to a
back-to-tank bypass valve and should be set to relieve at pressure 10 to 20
psi higher than the working bypass. Some built-in bypass valves have the
capability of being piped back-to-tank so check with the pump manufacturer.
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