Pumps developed head

F = Factor for fractionation allowable velocity or packed column packing factor or pump developed head, ft. 

For double suction pumps, using the HI convention, is taken as the total pump flow, although some pubHcations use half-flow, ie, flow per impeller eye. For multistage pumps, the developed head must be taken per stage for the NS calculation. By definition (eq. 9), high head, low flow pumps have low specific speed low head, high flow pumps, such as turbine and propeller pumps, have high specific speed. 

Eff. = Pump percentage efficiency F = Developed head, ft G = Flow, GPM... 

An approximate method to estimate pump efficiencies is based on the following formula. The expression is valid for flows between 100 and 1,000 gpm, and for developed heads between 50 and 300 ft. 

This shows that the pump head is determined primarily by the size and speed of the impeller and the pump efficiency, independent of the flow rate of the fluid. This is approximately correct for most centrifugal pumps over a wide range of flow rates. However, there is a limitation to the flow that a given pump can handle, and as the flow rate approaches this limit the developed head will start to drop off. The maximum efficiency for most pumps occurs near the flow rate where the head starts to drop significantly. 

Thus if a centrifugal pump develops a total head of 100 m when pumping a liquid of density p = 1000 kg/m3, the pressure developed is 981000 Pa while for p = 917 kg/m3 the pressure developed is 900000 Pa. 

A centrifugal pump develops the same feet of head, regardless of the density of the liquid pumped, as long as the flow is constant. This statement is valid as long as the viscosity of the liquid is below 40 cp or 200 SSU (Saybolt Seconds Universal). But, as process operators or engineers, we are not interested in feet of head. We are interested only in pressure. Differential pressure is related to differential feet of head as follows ... 

Answer The same elevation. Centrifugal pumps develop the same feet of head at a given volumetric flow rate, regardless of the specific gravity of the liquid pumped. This means the ability of the pump to push liquid uphill is the same, even if the density of the liquid changes. 

When needed, greater head or greater capacity may be obtained by operating several pumps in series or parallel. In parallel operation, each pump develops the same head (equal to the system head), and the flow is the sum of the flows that each pump delivers at the common head. In series operation, each pump has the same... 

Characteristic curves are plots or equations relating the volumetric flow rate through a pump to the developed head or efficiency or power or NPSH. 

The valves supplied with these pumps showed an erratic behavior at low flow rates, mainly due to a too large diameter of the valve balls and poor design of the valve seats and valve chambers. New pumpheads and valves were therefore developed, manufactured and mounted on the pumps. The heads and fittings were made from PVDF with valve seats and 3 mm diameter balls in acid resistant steel. On these pumps the stroke length has to be set mechanically and this set-screw was modified so that it could be turned by a simple manipulator, if necessary. The electronic frequency control was modified for remote operation. 

A centrifugal pump delivers 100 gpm of water at 60°F when the impeller speed is 1750 r/min and the pressure drop across the pump is 20 psi. If the speed is reduced to 1150 r/min, estimate the rate of water delivery and the developed head in feet if the pump operation is ideal. 

Pumping is a unit operation that is used to move fluid from one point to another. This chapter discusses various topics of this important unit operation relevant to the physical treatment of water and wastewater. These topics include pumping stations and various types of pumps total developed head pump scaling laws pump characteristics best operating efficiency pump specific speed pumping station heads net positive suction head and deep-well pumps and pumping station head analysis. 

The literature has used two names for this subject total dynamic head or total developed head (H or TDH). Let us derive TDH first by considering the system connected in parallel between points 1 and 2. Since the connection is parallel, the head losses across each of the pumps are equal and the head given to the fluid in each of the pumps are also equal. Thus, for our analysis, let us choose any pump such as the one with inlet g. From fluid mechanics, the energy equation between the points is... 

Total dynamic head or total developed head— The head given to the pump... 

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