液壓系統(tǒng)外文翻譯(參考版)
2025-01-09 09:24本頁(yè)面
【正文】 Some of the performance characteristics of different pumps are given in Table of these selection factors is described briefly in the following paragraph. The primary rating of a pump is its capacity. This is also called the delivery rate ,flow rate, or volumetric output. The capacity usually is given in gallons per minute (gpm), cubic inches per minute( ) ,or cubic inches per revolution at specified operating conditions. Pump capacity ratings usually are given at standard atmospheric inlet pressure and various output pressures, as well as at approximate fluid service temperatures. The pressure rating of a pump generally is based on the ability of the pump to withstand pressure without an undesirable increase in its internal leakage( or slippage) or damage to pump parts. Pumps are pressurerated under the same conditions( speed,temperrature,and inlet pressure) at which they are capacityrated. Most pumps are pressurerated at 100,500,1000,1500,2022,3500,or 5000 psi. Energy consumption is an important consideration not only in the selection of a pump, but also in the operating performance of the pump after the system is installed. The energy requirement for pumping depends on the pumping pressure, and on the mass of fluid pumped in a given time. Pumps often are rated at the monly available electric motor speed of 1200 or 1800 also may be rated at speeds other than motor speeds. For instance, higher speeds occur in mobile hydraulic pumps driven from internal bustion engines. These engines usually operate at a constant speed and include speeds of 2022 rpm and higher. Some industrial hydraulic pumps are rated at speeds of up to 4000 rpm. The safe speed for a rotating pump is limited by the pump’ s ability to avoid cavitation and high outlet pressures. Most rotating pumps also require a minimum operating speed. Although these speeds usually are not critical, pumps operating at high pressures require a minimum speed in order to prevent overheating or internal slippage. Maximum speed and pressure ratings for pumps often are given for both intermittent and continuous operation. Continuous ratings describe the maximum speed and pressure at which a pump can be operated for a normal design life (about 10000 hours). Intermittent ratings are maximum speed and pressure at which a pump can be operated safely for short times and still have a satisfactory service life. Operating a hydraulic pump beyond its drive speed ratings usually reduces its service life. As pointed out earlier, the pressure a system exerts on the hydraulic pump directly affects the delivery rate of the pump. As the pressure increases, the flow rate of the pump decreases. The amount of decrease varies depending on the type of pump used. This change in flow affects the pu
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