Basic Hydraulic Circuit Design Energy Conservation: Part 2

摘要

Farlier this year, we discussed the general concepts of energy conservation in fluid power systems. Now we'll take a look at specific types of systems and how they can be optimized to conserve energy. Demand flow systems are defined as those that use fluid sources which are responsive to the spontaneous flow rate demand of output devices and use close-center directional control valves, Examples of fluid sources are: accumulators, charged by fixed displacement pumps which are bypassed through an unloading valve during standby periods; or pressure-compensated variable displacement pumps, which deadhead during standby or overload conditions. The concepts for energy conservation previously discussed for constant flow systems apply equally to demand flow systems. The difficulty arises in providing a simple representation like that in Fig. 1 because △p vs. Q characteristics change constantly. Component sizing for a demand flow system should be made at maximum flow rates. The circuit designer may treat it as a constant flow system, with Q{sub}c = Q{sub}(max) for sizing purposes, knowing that energy losses will be smaller for lower flow rates. If peak flow demand is short of duration, it may be more economical to size for lower flows.