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

PLH_KKK_U2_31.QXP 25.05.2007 11:01 Uhr Seite 8FUNDAMENTALSA change in the duty point can generally onlybe achieved by changing the speed n or the impellerdiameter D of a pump in the case of radialimpellers.pValve authority∆p PQ 1 n 1=Q 2 n 2 H 2 n 2H 1 n 12= P 2 n 2P 1 n 12=Delivery head H [m]Delivery head H [m]Delivery head H [m]Change in flowChange in speedH 1n 1n 2H 2Q 1H 1B = duty pointn = speedQ 2Change in the impeller diameterø D 1ø D 2H 2Q 1Q 2Q 1 D 1 D 2 D 1Q 2 D 2 H 2 D 2H 1 D 12 D 2 D 1System curve H AB 1B 2B 3n 1n 2n 3D 1 D 2Q 2Q 1H 2H 1QH curvesFlow Q [m³/h]Flow Q [m 3 /h]Flow Q [m³/h]p 0Pump curve with valve authorityFor the working characteristics, it is importanthow high the pressure drop at the valve is whenthe valve is completely open with respect to thetotal pressure at the lines to be regulated. Thisratio is called the "valve authority P v ":∆p v100 ∆p v100P V = ==∆p ges ∆p v + ∆p rAbbreviationp 0∆p P∆p v∆p rp b∆p LV˙V˙100P VDescriptionMaximum pump pressurePressure loss in the pumpPressure drop at the valvePressure drop in the rest of the systemReference pressure of the systemPressure loss in the systemFlow∆p LFlow with valve completely openValve authorityPump curveNetwork curve0 0.2 0.4 0.6 0.8 1.0∆p v100∆p v0V˙/V˙100The last expression is especially practical froman instrumentation point of view because thevalve authority can be calculated from the pressuredrop at the open (∆p v100 ) and at the closedvalve (∆p vo ).p 0∆p v100 ∆p P100∆p L100∆p v8 Subject to change without prior notice 02/2007 WILO AG