外文翻譯--泵站中水泵的選型問題

1、<p><b>　　中文7762字</b></p><p>　　The pump in pumping station selection problem</p><p>　　Rotary pumps </p><p>　　These are built in many different designs and

2、 are extremely popular in modern fluid-power system. The most common rotary-pump designs used today are spur-gear, generated-rotary , sliding-vane ,and screw pump ,each type has advantages that make it the most suitable

3、for a given application .</p><p>　　Spur-gear pumps. these pumps 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 . th

4、e driving shaft is usually connected to the upper gear of the pump .</p><p>　　When the pump is first started ,rotation of gears forces air out the casing and into the discharge pipe. this removal of air from

5、 the pump casing produces a partial vacuum on 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

6、 discharge .</p><p>　　Pressure rise in a spur-gear pump is produced by the squeezing action on the fluid ad it is expelled from between the meshing gear teeth and casing ,.a vacuum is formed in the cavity be

7、tween the teeth ad unmesh, 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 way the quantity of fluid discharge b

8、y a spur-gear pump of type in figure can be regulated is by varying the shaft speed .modern gea</p><p>　　Figure shows the typical characteristic curves of a spur-gear rotary pump. These curves show the capac

9、ity and power input for a spur-gear pump at various speeds. At any given speed the capacity characteristic is nearly a flat line the slight decrease in capacity with rise in discharge pressure is caused by increased leak

10、age across the gears from the discharge to the suction side of the pump. leakage in gear pumps is sometimes termed slip. Slip also increase with arise pump discharge pressure .th</p><p>　　Power input to a sq

11、ur-gear pump increases with both the operating speed and discharge pressure .as the speed of a gear pump is increased. Its discharge rate in gallons per minute also rise . thus the horsepower input at a discharge pressur

12、e of 120psi is 5hp at 200rpm and about 13hp at 600rpm.the corresponding capacities at these speed and pressure are 40 and 95gpm respectively, read on the 120psi ordinate where it crosses the 200-and 600-rpm HQ curves .&l

13、t;/p><p>　　Figure is based on spur-gear handing a fluid of constant viscosity , as the viscosity of the fluid handle increases (i.e. ,the fluid becomes thicker and has more resistance to flow ),the capacity of

14、a gear pump decreases , thick ,viscous fluids may limit pump capacity t higher speeds because the fluid cannot into the casing rapidly enough fill it completely .figure shows the effect lf increased fluid biscosity on th

15、e performance of rotary pump in fluid-power system .at 80-psi discharge pressure </p><p>　　Capacity lf rotary pump is often expressed in gallons per revolution of the gear or other internal element .if the o

16、utlet of a positive-displacement rotary pump is completely closed, the discharge pressure will increase to the point where the pump driving motor stalls or some part of the pump casing or discharge pipe ruptures .because

17、 this danger of rupture exists systems are filled with a pressure –relief valve. This relief valve may be built as of the pump or it may be mounted in the discharge</p><p>　　Sliding-Vane Pumps,These pumps ha

18、ve a number of vanes which are free to slide into or out of slots in the pup rotor . when the rotor is turned by the pump driver , centrifugal force , springs , or pressurized fluid causes the vanes to move outward in th

19、eir slots and bear against the inner bore of the pump casing or against a cam ring . as the rotor revolves , fluid flows in between the vanes when they pass the suction port. This fluid is carried around the pump casing

20、until the discharge port is</p><p>　　In the sliding-vane pump in Figure the vanes in an oval-shaped bore. Centrifugal force starts the vanes out of their slots when the rotor begins turning. The vanes are he

21、ld out by pressure which is bled into the cavities behind the vanes from a distributing ring at the end of the vane slots. Suction is through two ports A and AI, placed diametrically opposite each other. Two discharge po

22、rts are similarly placed. This arrangement of ports keeps the rotor in hydraulic balance, reliving the bearing</p><p>　　Two vanes may be used in each slot to control the force against the interior of the cas

23、ing or the cam ring. Dual vanes also provide a tighter seal , reducing the leakage from the discharge side to the suction side of the pump . the opposed inlet and discharge port in this design provide hydraulic balance i

24、n the same way as the pump, both these pumps are constant-displacement units.</p><p>　　The delivery or capacity of a vane-type pump in gallons per minute cannot be changed without changing the speed of rotat

25、ion unless a special design is used. Figure shows a variable-capacity sliding-vane pump. It dose not use dual suction and discharge ports. The rotor rums in the pressure-chamber ring, which can be adjusted so that it is

26、off-center to the rotor. As the degree of off-center or eccentricity is changed, a variable volume of fluid is discharged. Figure shows that the vanes create a</p><p>　　Figure shows how maximum flow is avai

27、lable at minimum working pressure. As the pressure rises, flow diminishes in a predetermined pattern. As the flow decreases to a minimum valve, the pressure increases to the maximum. The pump delivers only that fluid nee

28、ded to replace clearance floes resulting from the usual slide fit in circuit components.</p><p>　　A relief valve is not essential with a variable-displacement-type pump of this design to protect pumping mech

29、anism. Other conditions within the circuit may dictate the use of a safety or relief valve to prevent localized pressure buildup beyond the usual working levels.</p><p>　　For automatic control of the dischar

30、ge , an adjustable spring-loaded governor is used . this governor is arranged so that the pump discharge acts on a piston or inner surface of the ring whose movement is opposed by the spring . if the pump discharge press

31、ure rises above that for which the by governor spring is set , the spring is compressed. This allows the pressure-chamber ring to move and take a position that is less off center with respect to the rotor. The pump theb

32、delivers less fluid, and</p><p>　　The characteristics of a variable-displacement-pump compensator are shown in figure. Horsepower input values also shown so that the power input requirements can be accuratel

33、y computed. Variable-volume vane pumps are capacity of multiple-pressure levels in a predetermined pattern. Two-pressure pump controls can provide an efficient method of unloading a circuit and still hold sufficient pres

34、sure available for pilot circuits.</p><p>　　The black area of the graph of figure shows a variable-volume pump maintaining a pressure of 100psi against a closed circuit. Wasted power is the result of pumping

35、 oil at 100psi through an unloading or relief valve to maintain a source of positive pilot pressure. Two-pressure –type controls include hydraulic, pilot-operated types and solenoid-controlled, pilot-operated types. The

36、pilot oil obtained from the pump discharge cannot assist the governor spring. Minimum pressure will result. The plus </p><p>　　Another type of two-pressure system employs what is termed a differential unload

37、ing governor. It is applied in a high-low or two-pump circuit. The governor automatically, Through pressure sensing, unloads the large volume pump to a minimum deadhead pressure setting. Deadhead pressure refers to a spe

38、cific pressure level established as resulting action of the variable-displacement-pump control mechanism. The pumping action and the resulting flow at deadhead condition are equal to the leakage in th</p><p>

39、;　　The governor is basically a hydraulically operated, two-pressure control with a differential piston that allows complete unloading when sufficient external pilot pressure is applied to pilot unload port.</p>&l

40、t;p>　　The minimum deadhead pressure setting is controlled by the main governor spring A. the maximum pressure is controlled by the relief-valve adjustment B. the operating pressure for the governor is generated by the

41、 large-volume pump and enters through orifice C. </p><p>　　To use this device let us assume that the circuit require a maximum pressure of 1000psi, which will be supplied by a 5-gpm pump. It also needs a lar

42、ge flow (40gpm) at pressure up to 500psi; it continues to 1000pso at the reduced flow rate. A two-pump system with an unloading governor on the 40-gpm pump at 500psi to a minimum pressure setting of 200psi (or another de

43、sired value) , which the 5-gpm pump takes the circuit up to1000psi or more.</p><p>　　Note in figure that two sources of pilot pressure are required. One ,the 40-gpm pump, provides pressure within the housing

44、 so that maximum pressure setting can be obtained. The setting of the spring, plus the pressure within the governor housing, determines the maximum pressure capacity of the 40-gpm pump. The second pilot source is the cir

45、cuit proper, which will go to 1000psi. this pilot line enters the governor through orifice D and acts on the unloading piston E . the area of piston E is 15 p</p><p>　　As pressure in the circuit increases fr

46、om zero to 500psi, the pressure within the governor housing also increases until the relief-valve setting is reached, at which time the relief valve cracks open, allowing flow to the tank.</p><p>　　The press

47、ure drop in the hosing is a maximum additive value, allowing the pump to deadhead. Meanwhile, the system pressure continues to rise above 700psi, resulting in a greater force on the bottom of piston E than on the top. Th

48、e piston then completely unseats poppet F, which results in a further pressure drop within the governor horsing to zero pressure because of the full-open position of the relief poppet F. flow entering the housing through

49、 orifice is directed to the tank pass the relief po</p><p>　　Axial Piston Pumps</p><p>　　In axial piston pumps of the in-line type, where the cylinders and the drive shaft are parallel ,the reci

50、procating motion is created by a cam plate, also known as a wobble plate ,tilting plate ,or swash plate .This plate lies in a plane plate that cuts across the center line of the drive shaft and cylinder barrel and does n

51、ot rotate .In a fixed-displacement pump ,the cam plate will be rigidly mounted in a position so that it intersects the center line of the cylinder barrel at an angle approxima</p><p>　　delivery axial piston

52、pumps are designed ,so that the angle that the cam plate makes with a perpendicular to the center line of the cylinder barrel may be varied from zero to 20 or 25 degrees to one or both sides. One end of each piston rod i

53、s held in contact with the cam plate as the cylinder block and piston assembly rotates with the drive shaft This causes the pistons to reciprocate within the cylinders .The length of the piston stroke is proportional to

54、the angle that the cam plate is set fr</p><p>　　A variation of axial piston pump is the bent-axis type is shown in 1-1 .This type does not have a tilting cam plate as the in-line pump does .Instead ,the cyli

55、nder block axial is varied from the drive shaft axis .The ends of the connecting rods are retained in sockets on a disc that turns with the drive shaft .The cylinder block is turned with the drive shaft by a universal jo

56、int assembly at the intersection of the drive shaft and the cylinder block shaft ,In order to vary the pump displacement </p><p>　　Figure 1-1 Bent –axis axial piston pump</p><p>　　The pumping ac

57、tion of the axial piston pump is made possible by a universal joint or link .Figure 1-2is a series of drawings that illustrates how the universal joint is used in the operation of this pump .</p><p>　　First

58、,a rocker arm is installed on a horizontal shaft .(See fig 1-1view A )The arm is joined to the shaft by a pin so that it can be swung back and forth ,as indicated in view B。Next, a ring is placed around the shaft and sec

59、ured to the rocker arm so the ring can turn from left to right as shown in view C, This provides two rotary motions in different planes at the same time and in varying proportions as may be desired .The rocker arm can sw

60、ing back and forth in one arc ,and the ring can simult</p><p>　　Next ,a tilting plate is added to the assembly .The tilting plate is placed at a slant to the axial of the shaft, as depicted in figure 1-1,vie

61、w D. The rocker arm is then slanted at the same angle as the tilting plate ,so that it lies parallel to the tilting plate .The ring is also parallel to ,and in contact with ,the tilting plate .The position of the ring in

62、 relation to the rocker arm is unchanged from that shown in figure 1-2,view C.</p><p>　　Figure 1-2view E shows the assembly after the shaft ,still in a horizontal position ,has been rotated a quarter turn .T

63、he rocker arm is still in the same position as the tilting plate and oscar now perpendicular to the axial of the shaft The ring has turned on the rocker pinstripe ,so that it has changed its position in relation to the r

64、ocker arm ,but it remains parallel to ,and in contact with the tilting plate .</p><p>　　View F of figure 1-2 shows the assembly after the shaft has been rotated another quarter turn. The parts are now in the

65、 same position as shown in view D, but with the ends of the rocker arm reversed ,The ring still bears against the tilting plate .</p><p>　　As the shaft continues to rotate ,the rocker arm and the ring turn a

66、bout their pivots ,with each changing its relation to the other and with the ring always bearing on the plate .</p><p>　　Figure 1-2, view G wheel added to the assembly .The wheel is placed upright and fixed

67、to the shaft ,so that rotates with the shaft .In addition ,two rods A and B, are loosely connected to the tilting ring and extend through two holes sanding opposite each other in the fixed wheel. As the shaft is rotated

68、,the fixed wheel turns perpendicular to the shaft at all times. The tilting ring rotates with the shaft and always remains tilted ,since it remains in contact with the tilting plate .Referring t</p><p>　　As

69、the assembly rotates ,the rods move in and out through the holes in the fixed wheel .This is the way the axial piston pump works. To get a pumping action , place pistons at the ends of the rods ,beyond the fixed wheel an

70、d insert them into cylinder .The rods must be connected to the pistons and to the wheel by ball and socket joints .As the assembly rotates ,each piston moves back and forth in its cylinder .Suction and discharge lines ca

71、n be arranged so that liquid enters the cylinder while th</p><p>　　The main parts of the pump are the drive shaft , pistons ,cylinder block , and valve and swash plates , There are two parts in the valve pla

72、te . These Portsmouth connect directly to openings in the face of the cylinder block . Fluid is drawn into one port and forced out the other port by the reciprocating action of the pistons .</p><p>　　Figure

73、1-2 Relationship of the universal joint in operation of the axial piston </p><p>　　IN-LINE-VARIABLE-DISPLACEMENT AXIAL-POSTON-PUMP------When the drive shaft is rotated , it rotates the pistons and the cylind

74、er block with it . The swash plate placed at an angle causes the pistons to move back and forth in the cylinder block while the shaft , piston , cylinder block and swash plate rotate together (The shaft piston , cylinder

75、 block , and swash plate together is sometimes referred to as the rotating group or assembly ) . As the pistons reciprocate in the cylinder block, fluid ent</p><p>　　The tilt or angle of the swash plate dete

76、rmines the distance the pistons move back and forth in their cylinder, thereby, controlling the pump output .</p><p>　　When the swash plate is at a right angle to the shaft, and the pump is rotating, the pis

77、tons do not reciprocate, therefore, no pumping action takes place. When the swash plate is tilted away from a right angle, the pistons reciprocate and fluid is pumped .</p><p>　　Since the displacement of thi

78、s type of pump is varied by changing the angle of the tilting box, some means must be used to control the changes of this movement-manual, electric, pneumatic, or hydraulic .</p><p><b>　　Gear pump<

79、/b></p><p>　　The concept of gear pump is very simple, that it is two of the most basic form of the same size gear in a close co-operation of mutual engagement with the rotating shell, the shell's inte

80、rnal similar "8" shape, the two gears mounted inside , the diameter of gear and work closely with both sides and shell. From the extruder the material inhaled into the mouth of two intermediate gears, and full

81、of the space, with the teeth along the shell of the rotary movement, the final two hours from the meshi</p><p>　　Speaking in terms of gear, also known as positive displacement pump device, that is, inside th

82、e cylinder like a piston, when a tooth to another tooth space of the fluid, the liquid was squeezed mechanically to row out. Because the liquid is incompressible, so the liquid and the tooth at the same time will not be

83、able to occupy the same space, so that the liquid has been ruled out. Because of the constant mesh gear, this phenomenon occurs on a row and, therefore, the pump provides a continuous ex</p><p>　　In fact, th

84、ere is little pump of the fluid loss, which makes the operation of pumps can not achieve 100% efficiency, as these fluids are used to on both sides of bearing and gear lubrication, and the pump body is also not possible

85、with no gap, it can not be so that 100% of fluid discharged from the export, so a small amount of fluid loss is inevitable. However, a good pump can be run out of material for the majority, will still be able to achieve

86、93% ~ 98% efficiency. </p><p>　　For the viscosity or density change in the process fluid, the pump will not be affected too much. If there is a damper, for example, in the export side, one row or a limiter f

87、ilter, pumps will push fluid through them. If the damper changes in their work, that is, if the filters become dirty, blocked, or limiter on the back of the hypertension, the pump will maintain a constant flow, until the

88、 device in the weakest parts of the mechanical limit (usually equipped with a torque limiter). </p><p>　　For a pump speed, in fact, there are restrictions, which mainly depends on the process fluid, if the t

89、ransmission is oil, pump can rotate at high speed, but when the fluid is a high viscosity of the polymer melt, such restrictions will be significantly reduced. </p><p>　　Promote blood flow into the intake si

90、de of the two tooth space is very important, if not fill in this space is full, the pump will not be able to discharge the flow of accurate, so the value of PV (pressure × velocity) is also a limiting factor, and is

91、 a process variable. As a result of these restrictions, gear pump manufacturers will provide a range of products, that is, different specifications and emission (per week to the emission of volume). These pumps will fit

92、the specific application of </p><p>　　PEP-II pump shaft gear and a total of one species hardened using technology, will be a longer working life. "D"-type bearing a combination of forced lubricatio

93、n mechanism, so that the polymer surface by the bearing, and return to the import side of pump to ensure effective lubrication of the rotation axis. This feature reduces the degradation of polymers and the possibility of

94、 being stranded. Precision machining of the pump body can "D"-type gear shaft with precision bearings to ensure non-eccen</p><p>　　PEP-II with a gear pump with the pump to match the specifications

95、of the heating elements for the user matching, which ensures rapid heating and heat control. Heating the body and pump in different ways, the damage to these components is limited to a board, the pump has nothing to do w

96、ith the whole. </p><p>　　Gear pump by an independent motor drive, to be effective in blocking the upper reaches of the pressure pulsation and flow fluctuations. Gear pump in the outlet of the pressure fluctu

97、ation can be controlled within 1%. In the extrusion production line using a gear pump, can increase the output flow rate of material in the extruder to reduce the shear and residence time to reduce the extrusion temperat