Pulsafeeder PulsaPro 900 EN - Manual (Page 15)

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4. A separate system relief valve to protect piping and process equipment, including the pump,
from excess process pressures.
a) The hydraulic bypass valve (HBV) in the pump is not intended to protect the system.
Piping weight must not be supported by valve housings or other portions of the reagent head, as
the resulting stresses can cause leaks. If appropriate, provide for thermal expansion and
contraction so that no excess force or movement is applied to the pump.
In piping assembly, use a sealing compound chemically compatible with the process material.
Users of sealing tape are cautioned to ensure that the entering pipe thread ends are not taped,
and that tape is removed from previously-used threads prior to re-use. Both new and existing
piping should be cleaned, preferably by flushing with a clean liquid (compatible with process
material) and blown out with air, prior to connection to the pump.
5.3.1 Suction Pressure Requirements
Although metering pumps have suction lift capability, all pump installations should be designed
to minimize lift for optimal performance. A flooded suction (i.e., suction fluid level higher than
the centerline of the pump) is preferable whenever possible. The pump should be located as
close as possible to the suction side reservoir or other source.
If suction lift is required, the minimum net positive suction pressure required (NPSH
R
) is 3
psia (0.21 bar) above the Vapor Pressure of the Process Fluid. If this requirement is not met
the Process Fluid may cavitate inside the pump, degrading metering accuracy.
Likewise, if the suction pressure is low enough, it is possible to cavitate the hydraulic fluid used
to move the diaphragm in the pump. Therefore, suction pressure must also be maintained at a
minimum absolute value of 5 psia (0.34 bar) to ensure proper hydraulic system and pump
operation.
The suction pressure must not exceed 165 psia (11.38 bar) for pumps with TFE diaphragms.
Please consult the factory for higher suction applications.
Higher pressures may be possible with optional alternate diaphragm materials or
modified dish plates.
Refer to Appendix I for a complete explanation of Suction Pressure Requirements including
methods to calculate values for your system.
5.3.2 Discharge Pressure Requirements
All Pulsafeeder Metering Pumps are designed for continuous service at the rated discharge
pressure. If system suction pressure were to exceed system discharge pressure (a condition
sometimes described as “pumping downhill” or “flow-through”), excess flow would be
generated, resulting in a reduction in accuracy and loss of control over the metering process. To
prevent this condition, the discharge pressure must exceed the suction pressure by at least 25
psia (1.7 bar). This can be achieved where necessary by installing a backpressure valve in the
discharge line.
D ISCHARGE PRESSURE MUST NEVER EXCEED THE HYDRAULIC BYPASS VALVE ( HBV )
SETTING ON THE NAMEPLATE . E XCESSIVE DISCHARGE PRESSURE COULD IMPAIR
PERFORMANCE , DAMAGE THE PUMP AND VOID THE WARRANTY .
Refer to Appendix I for a complete explanation of Discharge Pressure Requirements including
methods to calculate values for your system.