中英文文献翻译—液压泵的简单介绍

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The commonly used sources of power in hydraulic systems are pumps and accumulators .

Similarly,accumulator connected to atmosphere will dischange oil at atmosphere pressure until it empty. only when connected to a system having resistance to flow can pressure be developed.

Three types of pumps find use in fluid-power systems: 1,rotary,2,reciprocating,3,or piston-type,and 3,centrifugal pumps.

Simple hydraulic system may use but one type of pump . The trend is to use pumps with the most satisfactory characteristics for the specific tasks involved . In matching the characteristics of the pump to the requirements of the hydraulic system , it is not unusual to find two types of pumps in series . For example , a centrifugal pump may be to supercharge a reciprocating pump , or a rotary pump may be used to supply

pressurized oil for the contronls associated with a reversing variabledisplacement

pumps .

Most power systems require positive displacement pumps . At high pressure , reciprocating pumps are often preferred to rotary pumps .

Rotary pumps

These are built in many differnt designs and extremely popular in modern fluid power system . The most common rotay-pump designs used today are spurgear ,

internal gear ,generated rotor , sliding vane ,and screew pumps . Ehch type has

advantages that make it most suitable for a given application .

Gear pumps

Gear pumps are the simplest type of fixed displacement hydraulic pump available . This type consists of two external gear , generally spur gear , within a

closed-fitting housing . One of the gear is driven directly by the pump drive shaft .

It ,in turn , then drives the second gear . Some designs utilize helical gears ,but the spur gear design predominates . Gear pumps operate on a very simple principle , illustration Fig.7.3 . As the gear teeth unmesh , the volume at the inlet port A expands , a partial vacuum on the suction side of the pump will be formed . Fluid from an external

reservoir or tank is forced by atmospheric pressure into the pump inlet . The

continuous action of the fluid being carried from the inlet to the discharge side B of the pump forces the fluid into the system .

Pressure rise in a spur-gear pump is produced by the squeezing action on the fluid as it is expellde from between the meshing gear teeth and the casing . Fluid from the discharge side is prevented from returing to the inlet side by the clearance between the gears and houseing .

Vane pumps

The vane pump ,illustration 7.4 , consists of a housing that is eccentric or offset with respect to the drive shaft axis . In some models this inside surface consists of a cam ring that can be rotated to shift the relationship between rotor are rectangular and extend radially from a center radius to the outside diameter of the rotor and from end to end . A rectangular vane that is essentially the same size as the slot is inserted in the slot and is free to slide in and out .

As the rotor turns , the vanes thrust outward , and the vane tips track the inner surface of the housing , riding on a thin film of fluid . Two port or end plates that engage the end face of the ring provide axial retention .

Centrifugal force generally contributes to outward thrust of the vane . As they ride along the eccentric housing surface , the vane move in and out of the rotor slots . The vane divide the area between the rotor and casing into a series of chambers .The sides of each chamber are formed by two adjacent vanes ,the port or end plates , the pump casing and the rotor . These chambers change in change in volume depending on their respective position about the shaft .

As each chamber approaches the inlet port , its vanes move outward and its volume expands , causing fluid to flow into the expanded chamber . Fluid is then carried within the chamber around to the dischange port . As the chamber approaches the discharge port , its vanes are pushed inward ,the volume is reduced , and the fluid is forced out the discharge port .

The variable-volume vane pump can be adjusted to discharge a different volume of fluid while running at constant speed , simply by shifting the cam ring with respect to the rotor .When the pump components are in position such that the individual chambers achieve their maximun volume as they reach the inlet port , the maximum volume of fluid will be moved . If the relationship between housing and rotor is changed such that the chambers achieve their minmum of zero volume as they reach the inlet port , the pump delivery will be reduced to zero .

Since the vane pump housing or cam ring must be shifted to change the eccentricity and vary the output , variable-displacement vane pumps cannot have the closed end fit common to fixed-displacement vane pumps . Volumetric efficiency is in the range of 90% to 95% . These pumps retain their efficiency for a considerable length of time since compensation for wear between the vane ends and the housing is automatic .As these surfaces wear , the vanes move farther outward from their slots to maintain contact with the housing .

Vane pump speed is limited by vane peripheral speed . High peripheral speed will