Pumps minimum flow bypass

A jockey pump maintains pressure on the firewater system at all times. The set pressure will typically be in the range 8—lObarg. Generally, the jockey pump will mm itself on and off depending on the header pressure. If the pump mns continuously its discharge should recirculate through a minimum flow bypass. 

When a blocked discharge could be a problem, or when large turndown ratios are anticipated, the installation of a minimum flow bypass should be considered. This type of bypass opens when the flow of liquid leaving the pump falls below a minimum value. The bypass returns discharge liquid to the suction of the pump. Since the liquid is heated as it goes through the pump, it may be necessary to put a cooler on the recycle stream, or to have the recycle stream flow to a suction tank or vessel that contains a large inventory of liquid. 

If upon a reduction in load, the speed of a compressor is reduced, Vd — Pt mill also decrease, and with it, the minimum flow requirement for surge protection. Thus with speed as the manipulated variable, the bypass valve usually does not need to be opened. Together with the reasons mentioned under centrifugal pumps, this makes manipulation of speed economically attractive. 

If we shut off the pump in the system in Prob. 6.56 and open the bypass around it, what are the j maximum and minimum values of the flow Which way does it go Neglect the friction losses in the pump bypass line. Assume that the globe valve is always wide jjpen. 

If the pump in problem 3-23 is shut and the bypass opened, what will be the direction of flow What will the minimum and maximum flow rate values be ... 

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