MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

24whereyWis the specific weight of water and K is a constant whichdepends on the unitsof measurement used for the other terms.Of course, since water lifting devices like any other machinery havelosses (e.g., internal friction, slippage, leakage, etc.), in order toadd a given WHP to the water, some higher brake horsepower (BHP) willhave to be applied to the pump. This BHP will be the energy which mustbe delivered to the pump by its prime mover. It should be noted herethat this parameter of power is not limited to mechanical prime movers, butthat manual and animal BHP can be determined to evaluate the performanceof water lifters utilizing such mears of motivation.2.2.4 Efficiency (Eff)The efficiency of a water lifter is the ratio of energy added to thewater over the energy put into the device to obtain the increase in waterenergy,or put in terms of power,WHPEff=m . (2.15)An efficiency can also be calculated for the prime mover which suppliesthe BHP to the water lifter. Where the method of transmitting this primemover power (BHP) to the water lifter is not direct, losses may alsooccur in the transmission. For example, when belts are used between amotor and pump, slippage and heat losses occur which prevent getting allthe motor’s output power to the pump. Thus, an efficicney for the trans-missioncan also be calculated.