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

PLH_KKK_U2_31.QXP 25.05.2007 11:02 Uhr Seite 31PUMP INTAKESuctioningThe standard circulation pumps are not selfpriming.This means that the suction line andthe pump housing on the suction side have to bevented so that the pump can work. If the pumpimpeller is not under the fluid level, the pumpand suction line must be filled with fluid. Thistedious procedure can be avoided when the inletof the suction pipe is equipped with a foot valve(non-return valve). Venting is only required atthe initial commissioning or when a fitting isleaky.Foot valveSuction operationDue to losses in the connection lines, pump andfittings, a maximum of 7 to 8 m suction head canbe achieved in practice. The head difference ismeasured from the surface of the water level tothe pump suction port.Suction lines are to be installed which have atleast the nominal diameter of the pump port,but if possible, should be one nominal diameterlarger. Reductions are to be avoided. Especiallyfine filters must be kept away from the suctionside. The suction line is to be installed so that ithas a continuous incline to the pump and a footvalve (floating discharge) is to be installed whichprevents the line from running empty. The lineshould be kept as short as possible. In long suctionlines, increased friction resistances arisewhich strongly impair the suction head.Air pocket formation caused by leaks are to beavoided under all circumstances (pump damage,operating faults).When hose lines are installed, suction- andpressure-proof spiral hoses should be used.Suction line installationcorrectincorrectWilo Planning Guide - Refrigeration, air-conditioning and cooling technology 08/2006 31