Cracking Pressure

The pressure at which the relief valve begins to open and bypass liquid. Calculating: This value can be given by the customer or established at 10-15% above the maximum differential pressure for pumps with internal relief valves or the maximum discharge pressure for pumps with return-to-tank valves or in-line system valves.

Full Bypass Pressure

The pressure at which the entire capacity of the pump is bypassing through the relief valve. In other words, this is the maximum differential pressure rating for pumps with internal relief valves or the maximum discharge pressure rating for pumps with return-to-tank valves or in-line system valves.

Calculation: Dependent on the valve used, spring used, and capacity of the pump.

Maximum Allowable Casing Pressure

Maximum rated pressure of the pressure containing components of the pump, not including the shaft seal, but including the canister in the case of Mag Drive pumps. Calculating: MACP can be established as the pressure limit of the port connections for most pump models. In the case of Mag Drive pumps, it can be considered as the hydrostatic limit of the canister divided by 1.5.

Maximum Differential Pressure

The maximum allowable difference between the Discharge Pressure and the Inlet Pressure for a given set of operating conditions. 

Calculating: Provided by the Pump Selector program or Catalog Performance Curves, but may be increased or decreased depending on the application specifics, pump size, and construction. This may be less than or equal to the Full Bypass Pressure of the relief valve. 

Differential Pressure

The difference between the Discharge Pressure and the Inlet Pressure.   Calculating: Differential pressure is a function of the system and must be calculated or measured. Measurements can be made at the gauge ports near the inlet and outlet ports of the pump.

Discharge Pressure

Pressure at the outlet port of the pump. Calculating: Discharge pressure is a function of the system and must be calculated or measured. Measurements can be made at the gauge port on the outlet side of the pump or at a point on the outlet pipe as close as possible to the pump.
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