Hydraulic systems can use either of two methods of load control: energy-loss, in which flow to the actuator is set by valving, or volume-control, in which the stroke of a variable-displacement pump sets the rate at which fluid flows to the actuator. Although systems using variable-displacement pumps inherently are more efficient, they are more costly and cannot react as quickly as systems using servo or proportional valves operating from a constant pressure source.
Most industrials hydraulic systems care designed using the energy loss method. Such
systems cost less to build and are more responsive because system energy is
immediately available. But because of the inherent poor efficiency of these systems, energy lost as heat can exceed that of the mechanical power produced by the system.
Even well-designed electrohydraulic servovalve or proportional valve systems may
convert 60 to 80% of input horsepower to heat. Well-designed non-servo systems can
produce heat losses of only 20 to 30%.
www.dhtnet.com
