Pump suction pressure

Throttling of pump discharge may also be used to provide finer control and to permit operation when pump suction pressure may be inadequate for full flow operation. 

The pump suction pressure is constant at 10 psig. The design flow rate is 500 gpm. At this flow rate the pressure drop over the flow orifice is 2 psi, through the piping is 30 psi, over three heat exchangers is 32 psi, and over the furnace is 60 psi. Assume a flat pump curve and a specific gravity of 1. 

The boiling-point pressure of the water is equal to 30 psig that is, we can assume that the water draw-off is at its bubble-point pressure. At 36 psig pump suction pressure, the available NPSH is then... 

Liquids in storage tanks are almost always subcooled. This is so because otherwise the ambient vapor losses from the tank s vent, would be excessive. This creates the potential for a negative pump suction pressure. 

Second, please note that the control valve s required pressure loss is to be governed by a 20% factor of the overall two-part pipe run pressure drop. This is good and accepted practice. The total shown is our first guess of the pump discharge pressure. Of course, the positive remaining pump suction pressure must also be added to get the pump discharge pressure in psig. 

Note If pump suction pressure is greater than 150 psig, then Fp = 1.50 otherwise, Fp = 0. 

Pump suction pressure switch contacts opened. Break or leak in chlorine vacuum line piping. 

Normal pump flow, m /h Pump head, m water head Pump suction pressure, MPa Pump discharge pressure, MPa Pump speed, rpm Rundown time (1/2 speed), s Pump weight, t Total pump power (normal operation), MW Total pump power (all pumps operating), MW Distributor headers per loop Coolant circuit material... 

Vg = actual pumping capacity required, ACFM Pj = pump suction pressure Pgo = vapor pressure of water at 60 F... 

Power requirements can be estimated based on the flowrate (FDA equiva-ient) and the suction pressure. This method uses the equation below and is approximate only although it correlates well with test data especially for liquidring pumps. Suction pressures should be limited to the range of 10 to 500 torr. 

Bottoms level, 14, 293 Bottoms sediment and water, 27 Bottoms stripper, 22 Bottoms-pump suction pressure loss (vacuum towers), 281-285 insufficient quench, 283-284 trim gas oil pan overflows, 284 gland oil, 284 suction screen, 284 air leak, 285... 

Vacuum tower wash oil, 165 Vacuum lowers, 281—300 bottoms-pump suction pressure loss, 281— 285 high flash-zone pressure, 285-288 ejector problems, 288-292 black gas oil, 292-293 trim gas oil production, 293 pumparound draw temperatures, 293 light resid, 294 steam-to-healer passes, 295-297 gas-oil recovery improvement, 297-298 transfer-line failures, 298-299 troubleshooting problems, 299-300... 

The pressure of the gland oil or seal flush fluid to the seal should be roughly 30 psi higher than the pump suction pressure. This is a fine point many operators miss. Too high a pressure can damage the seal. 

A potential case of ulcers was avoided by relocating the 10% caustic addition point. Figure 14-2 shows this point just upstream of the caustic circulation control valve. The system was revamped to add 10% caustic into the suction of the circulating pump. The pump suction pressure was 50 psi lower than the pump discharge pressure. 

Net positive suction head available is the difference between the pump suction pressure and the saturation pressure for the liquid being pumped. 

Note that this pump will increase the pressure of the influent water by 250 psi over the pump suction pressure. If the suction pressure is 10 psig, the discharge pressure will be 260 psid). The curve also indicates that the net pressure suction head required (NPSHr) to prevent cavitation of the pump is about 3.45 psi (8.0 feet of water). The efficiency of the pump is about 68%, just about the maximum efficiency for this pump. This pump would be quite suitable for use in the specified RO application. However, in the case where the actual pump efficiency was far from the theoretical maximum, another pump would need to selected that would yield higher pump efficiency. Motor efficiencies nm at about 90%. Each pump and motor combination has its own specific pump curve. 

Further reduction of pressure by pumping gaseous CO2 from the extractor into the storage vessel via a condenser. The pump suction pressure progressively falls during this operation, finally coming to a value between 2 and 8 bar which is set by the capabilities of the pump. The pump requirements are discussed further in sections 9.4 and 5.7.1... 

Measure the pump suction pressure, and add the barometric pressure (14.67 psia at sea level). 

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