Refrigeration, air-conditioning and cooling technology - 2007.pdf

PLH_KKK_32_85.QXP 25.05.2007 10:11 Uhr Seite 55FUSE PROTECTION OF PUMPS AND REFRIGERATING MACHINESType of controlPumps which serve as admission pressure pumpsare only to be switched on/off when the volumedecrease through the secondary pump circuitlies at the required minimum/ maximum flowvolume. When several admission pressure pumpsare operating in parallel, an automatic switchon/offof the individual pumps within their permittedworking ranges is required.Circulating pumps in secondary circuits are onlyto be switched on when the primary circuit isdelivering the required minimum volume. Theyare to be switched off when the admission pressurepump provides so much pressure that thevolume flow is too high.If there is an on-site, stepless speed control,the minimum and maximum speed are to be limitedso that there is no overloading and the motorself-cooling function is guaranteed. Throttleand bypass controllers in the pump circuit areto be configured so that the maximum and minimumpermitted volume flows are always guaranteed.It makes sense to monitor the fluid temperaturewith an automatic limit shut-downfunction on the pump.The parallel operation of pumps and the simultaneousstepless control of one, several or allpumps is only possible with a load-sensitive,automatic switch-on/off or cut-in functionwithin the permissible limits of the flow anddelivery head of the individual aggregates.In order to avoid malfunctions and damage, theadmission pressure/pressurising system is to bemonitored. Because of the constantly changingpressures in controlled pump circuits, a differentfeed flow is always possible.Wilo Planning Guide - Refrigeration, air-conditioning and cooling technology 02/2007 55