MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

20HDD = H SD + HFD + HP ’ (2.7)(1) Total dynamic head (HTD) , also referred to as effective heador just total head, is the entire energy potential of the systemagainst which the water lifter or pump must operate. Where asuctionhead exists,HTD = HDD - ‘DSH ’(2.81but where a suction lift is present,‘irD = HDD + HDSL -(2.93As shown in Figure 2.1, the total static head will remain constantfor any discharge of the water lifting system. However, because velocityincreases with discharge, the velocity and friction heads, being a directfunction of velocity, will increase. Similarly, in applications of highcapacity pumps in wells, or where a fixed or slow recharging water supplyexists, drawdown also increases with discharge. Thus, as the discharge ofa pump increases, the total head against which it must operate alsoincreases, as illustrated in the example system head curve of Figure 2.1.Two additional head terms need to be discussed concerning any waterlifting device which operates with a dynamic suction lift. They applyparticularly (but not limited) to rotodynamic pumps, which cannot displaceair sufficiently enough to reduce intake pressure and thus llsuck” water.--Net Positive Suction Head Required (NPSHR) is a function of aspecific pump’s design and is determined by the pump manufacturer. 1