Nova-Tech LMI Series G - SD Metering Pump - Manual (Page 14)

2.6.1 NPSH CONSIDERATIONS
Size piping to accommodate peak instantaneous flow.
Because of the reciprocating motion of the pump dia-
phragm, peak instantaneous flow is approximately equal
to 5 times the average flow. For example, a pump rated
for 16 gallons per hour (61 L/hr.) requires piping suffi-
cient for 5 x 16 gph, or 80 gph (303 L/hr.).
To minimize viscous flow losses when handling viscous
liquids, it may be necessary to use suction piping up to
four times larger than the size of the suction connection
on the pump. If in doubt, contact your dealer to deter-
mine the necessary pipe size.
2.6.2 GENERAL PIPING CONSIDERATIONS
Use extreme care in piping to plastic liquid end pumps
with rigid pipe such as PVC. If excessive pipe stress or
vibration is unavoidable, flexible connections are rec-
ommended.
Use piping materials that will resist corrosion by the
liquid being pumped. Use care in selecting materials to
avoid galvanic corrosion at pump liquid end connections.
Use piping heavy enough to withstand maximum pres-
sures. Remove burrs, sharp edges, and debris from
inside piping. Blow out all pipelines before making final
connections to pump.
Because vapor in the liquid end will cause inaccurate
pump delivery, piping should be sloped up from pump
suction check to the supply tank to prevent formation of
vapor pockets.
When pumping suspended solids (such as slurries), in-
stall plugged crosses at all 90° line turns to permit line
cleaning without dismantling piping.
See Figure 5 for a typical recommended pump installa-
tion scheme.
2.6.3 SUCTION PIPING CONSIDERATIONS
It is preferable to have the suction of the pump flooded
by locating the liquid end below the lowest level of the
liquid in the supply tank.
To minimize the chances of a loss-of-prime condition,
the pump should be installed as close as possible to
the supply vessel.
Avoid negative suction pressure conditions (suction lift),
as such conditions adversely affect metering accuracy.
A lift of 6.6 feet (2 meters) of water column is the maxi-
mum permissible suction lift.
Series G pumps are designed to operate with process
liquid supplied at or above atmospheric pressure. Al-
though these pumps can move liquids supplied at less
than atmospheric pressure (suction lift), in these nega-
Figure 5:
General Piping
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