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5
5.3 Suction Pressure Requirements
Although OMNI
®
metering pumps have some suction lift capability, a flooded suction (i.e., suction
pressure higher than atmospheric pressure) is preferable whenever possible. The pump should be
located as close as possible to the suction side reservoir or fluid supply source.
For fluid with a vapor pressure of 5 psia or less (at operating temperature) the wet suction lift capability
is approximately ten (10) feet. If this requirement is not met, the pump will not provide reliable,
accurate flow. In suction lift conditions, the use of a foot valve is recommended at the lowest point of
the pickup tube or pipe. Pumps under suction lift conditions may require some liquid priming before
they will operate reliably.
5.4 Discharge Pressure Requirements
All OMNI
®
metering pumps are designed for continuous service at the rated discharge pressure. If
system suction pressure exceeds discharge pressure (a condition sometimes described as “pumping
downhill”), flow would be generated (siphoning) in addition to that caused by the pump. This results in
a reduction in accuracy and loss of control over the metering process. To prevent this flow-through
condition, the discharge pressure must exceed suction pressure by at least 0.35 Bar (5 psi). This can be
achieved where necessary by the installation of a backpressure valve in the discharge line. Conditions
where the actual discharge pressure exceeds the pump’s rating are to be avoided as they will cause
damage to the pump components.
Figure 3, sample system configuration