往复盾构机顶管专用泵

往复盾构机顶管专用泵泵是容积泵的一种,它依靠盾构机顶管专用泵在泵缸中往复运动，使泵缸工作容积呈周期性的扩大与缩小来吸排液体。往复盾构机顶管专用泵泵具有自吸能力，且在压力剧烈变化下仍能维持几乎不变的流量,它特别适用于小流量、高扬程的情况下输送黏性较大的液体。在油库中,往复盾构机顶管专用泵泵的主要用途是输送专用燃料油和润滑油，还可以作为锅炉给水泵或为离心泵抽真空引油、抽罐车底油等。由于往复盾构机顶管专用泵泵结构复杂，易损件多，流量有脉动，大流量时机器笨重，所以在许多场合为离心泵所代替。但在高压力、小流量、输送黏度大的液体，要求精确计量并要求流量随压力变化小的情况下仍采用各种型式的往复盾构机顶管专用泵泵。
一、往复盾构机顶管专用泵泵的结构和工作原理

如图2-6所示，往复盾构机顶管专用泵泵的主要部件有泵缸、盾构机顶管专用泵、盾构机顶管专用泵杆、吸入阀和排出阀。吸入阀和排出阀均为单向阀。电动往复盾构机顶管专用泵泵通常是用曲柄连杆机构,把电动机的旋转运动变为盾构机顶管专用泵的往复运动。当盾构机顶管专用泵向右移动时，泵缸的容积增大而形成低压。排出阀受排出管内液体压力作用而关闭;吸入阀受贮槽液面与泵缸内的压差作用而打开,使液体吸入泵缸。当盾构机顶管专用泵向左移动时,由于盾构机顶管专用泵的推压,缸内液体压力增大,吸入阀关闭，排出阀开启,使液体排出泵缸，完成一个工作循环。盾构机顶管专用泵在泵缸内两端间移动的距离，称为行程。
    盾构机顶管专用泵在泵缸内往复一次只有一次排液的泵，称为单作用泵，如图2-6所示。当盾构机顶管专用泵两面都作用，即一面吸入，另一面就排出,这时一个往复行程内完成两次吸排过程.其流量约为单作用泵的两倍.称为双作用泵,如图2-7所示。
    往复盾构机顶管专用泵泵启动前不用灌泵，能自动吸入液体,即有自吸能力。但实际操作中，仍希望在启动时泵缸内有液体，这样不仅可以立即吸、排液体,而且可避免盾构机顶管专用泵在泵缸内干摩擦，以减少磨损。往复盾构机顶管专用泵泵的转速(即往复频率)对泵的自吸能力有影响。若转速太大，液体流动阻力增大，当泵缸内压力低于液体饱和蒸气压时，会造成泵的抽空而失去吸液能力。因此,往复泵转速n不能太高，一般在80~ 200r/min之间,吸入高度(安装高度)为4~ 5m。

Special pump for pipe jacking of reciprocating shield machine

The special pump for pipe jacking of reciprocating shield machine is a kind of positive displacement pump. It depends on the reciprocating motion of the special pump for pipe jacking of shield machine in the pump cylinder, which makes the working volume of the pump cylinder expand and shrink periodically to absorb and discharge liquid. The special pump for pipe jacking of reciprocating shield machine has self-priming capacity, and it can maintain almost constant flow under the condition of drastic pressure change. It is especially suitable for conveying viscous liquid under the condition of small flow and high head. In the oil depot, the main purpose of the special pump for pipe jacking of reciprocating shield machine is to transport the special fuel oil and lubricating oil. It can also be used as the boiler feed water pump or the centrifugal pump to pump the vacuum oil and the bottom oil of the tank car. Due to the complex structure of the special pump for pipe jacking of reciprocating shield machine, many vulnerable parts, pulsating flow and heavy machine in large flow, it is replaced by centrifugal pump in many occasions. However, in the case of high pressure, small flow and high viscosity liquid transportation, which requires accurate measurement and small flow variation with pressure, various types of special pump for pipe jacking of reciprocating shield machine are still used.

1、 Working principle of reciprocating pump for shield machine

As shown in Figure 2-6, the main components of the special pump for pipe jacking of reciprocating shield machine are pump cylinder, special pump for shield top pipe, special pump rod for shield top pipe, suction valve and discharge valve. Both the suction valve and the discharge valve are one-way valves. The special pump for pipe jacking of electric reciprocating shield machine usually uses crank connecting rod mechanism to change the rotary motion of motor into the reciprocating motion of special pump for pipe jacking of shield machine. When the special pump for pipe jacking of shield machine moves to the right, the volume of pump cylinder increases and low pressure is formed. The discharge valve is closed by the liquid pressure in the discharge pipe; the suction valve is opened by the liquid level in the storage tank and the pressure difference in the pump cylinder, so that the liquid is sucked into the pump cylinder. When the special pipe jacking pump of shield machine moves to the left, due to the push of the special pipe jacking pump of shield machine, the liquid pressure in the cylinder increases, the suction valve closes and the discharge valve opens, so that the liquid is discharged from the pump cylinder and a working cycle is completed. The distance between the two ends of the special pump in the pump cylinder is called the stroke.

The special pump for shield top pipe reciprocates in the pump cylinder once and only discharges liquid once, which is called single acting pump, as shown in Figure 2-6. When both sides of the special pump for pipe jacking of shield machine work, that is, one side inhales and the other side discharges, the two suction and discharge processes are completed in a reciprocating stroke. The flow rate is about twice that of the single acting pump. It is called double acting pump, as shown in Figure 2-7.

The special pump for pipe jacking of reciprocating shield machine can automatically inhale liquid without filling the pump before starting, that is, it has self-priming capacity. However, in actual operation, it is still expected that there will be liquid in the pump cylinder when it is started, which can not only absorb and discharge the liquid immediately, but also avoid the dry friction of the special pump for pipe jacking of shield machine in the pump cylinder, so as to reduce the wear. The rotation speed (i.e. reciprocating frequency) of the special pump for pipe jacking of reciprocating shield machine has an influence on the self-priming capacity of the pump. If the rotation speed is too high, the liquid flow resistance increases, when the pressure in the pump cylinder is lower than the liquid saturated vapor pressure, the pump will be evacuated and lose the suction capacity. Therefore, reciprocating pump speed n can not be too high, generally between 80 ~ 200R / min, suction height (installation height) is 4 ~ 5m.