Book - School of Science and Technology

System arrangements 619C.W. feedFlowC.W. feedFlowPumpReturnPumpReturn(a)(b)Figure 21.13 Circulating pumps for secondary systemsrequired in circulation to counter heat loss. It is necessary, therefore, to introduce a bypass, incorporating a non-return valve, around the pump to avoid outflow being inhibited.During times other than of high demand, water will pass through the pump creatingstagnant conditions in the bypass line, thereby allowing the possible development oflegionella. Positioning the circulation pump on the return without a bypass obviatesthis problem.As in the case of heating systems, centrifugal-type pumps are best suited to thecirculation of the comparatively small quantities of water involved. The pump bodyshould be of a pattern which may be opened for cleaning and removal of any scale andshould preferably be made of a copper alloy which is compatible with the pipe materialsused in the system. Submerged rotor pumps are generally unsuitable for service in thesecondary pipework of hot water systems.