1、中英文资料（一）Hardened gear reducer prices and AnalysisThe purpose of the pump ,to give pressure to the oil ; in other words, to give power to the machine .The purpose of the valves is to control the flow of oil and to apply the power when and where it may be needed .To illustrate as simply as possible ho
2、w this is accomplished in a “circuit”, that is , in the run of oil from the reservoir ,through the pump , the valves , the driven unit , and back to the reservoir, references are made to the diagrams shown in Figs,11.1 and 11.2. Every fluid-power system used one or more pumps to pressurize the hydra
3、ulic fluid the fluid under pressure, in turn, performs work in the output section of the fluid-power system. Thus, the pressurized fluid may be used to move a piston in a in a cylinder or to turn the shaft of a hydraulic motor. So we find that find that every modern fluid power system used at least
4、one pump to pressurize the fluid.TYPES OF PUMPSThree types pumps find use in fluid-power systems: rotary , reciprocating, and centrifugal pumps . Simples hydraulic systems may use but one type of pump, The trend is to use pumps with the most satisfactory characteristics for the specific tasks involv
5、ed . 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 may be used to supercharge a reciprocating pump , or a rotary pump may be used to supply pressurized oil for
6、the controls associated with a reversing variable-displacement reciprocating pump .ROTARY PUMPSThese are built in many different designs and are extremely popular in modern fluid-power system. The most common rotary-pump designs used today are spur gear , internal-gear , generated rotor , sliding-va
7、ne , and screw pump . Each type has advantages that make it most suitable for a given application. Spur-Gear Pumps. These pumps (Fig.11.3) have two mating gears are turned in a closely fitted casing. Rotation of one gear, the driver, causes the second , or follower gear , to turn . The driving shaft
8、 is usually connected to the upper gear of the pump . When the pump is first started , rotation of gears forces air out the casing and into the dis-charge pipe . This removal of air from the pump casing produces a partial vacuum on the suction side of the pump . Fluid from an external reservoir is f
9、orced by atmospheric pressure into the pump inlet . Here the fluid is trapped between the teeth of the upper and lower gears and the pump casing. Continued rotation of the gears forces the fluid out of the pump discharge. Pressure rise in a spur-gear pump is produced by the squeezing action on the f
10、luid as it is expelled from between the meshing gear teeth and casing . A vacuum is formed in the cavity between the teeth as they unmeshed , causing more fluid to be drawn into the pump . A spur-gear pump is a constant-displacement unit ;its discharge is constant at a given shaft speed . The only w
11、ay the quantity of fluid discharged by a spur-gear pump of the type in Fig,11.3 can be regulated is by varying the shat speed . Modem gear pumps used in fluid-power systems develop pressure up to about 3000psi. SLIDING-VANE PUMPS SLIDING These pumps have a number of vanes which are free to slide int
12、o or out of slots in the pump rotor . When the rotor is turned by the pump driver , centrifugal force , springs , or pressurized fluid causes the vanes to move outwad in their slots and bear against the inner bore of the pump casing or against a cam ring . As the rotor revolves, fluid flows in betwe
13、en the vanes when they pass the suction port . This fluid is carried around the pump casin until the discharge port is reached . Here the fluid is forced out of the casing and into the discharge pipe.CONTROL VALVESPressure control valves are used in hydraulic circuits to maintain desired pressure le
14、vels in various parts o the circuits . A pressure-control valve maintains the desired pr4essure level by diverting higher-pressure fluid to a lower-pressure area , or restricting flow into another area . Valve that divert fluid can be safety , relief , counter-balance , sequence , and unloading type
15、s , Valves that restrict flow into another area can be of the reducing type . A pressure-control valve may also be defined as either a normally closed or normally open two-way valve . Relief , sequence , unloading and counterbalance valves are normally closed , two-way valves that are partially or f
16、ully open while performing their design function . A reducing valve is a normally open valve that restricts and finally blocks fluid flow into a secondary area . With either type of operation , the valve can be said to create automatically an orifice to provide the desired pressure control . An orifice is not always created when the valve is piloted from an external source .One valve of this type is the unloading valve it is not self-operating
