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往復盾構機頂管專用泵

往復盾構機頂管專用泵泵是容積泵的一種,它依靠盾構機頂管專用泵在泵缸中往復運動，使泵缸工作容積呈周期性的擴大與縮小來吸排液體。往復盾構機頂管專用泵泵具有自吸能力，且在壓力劇烈變化下仍能維持幾乎不變的流量,它特別適用于小流量、高揚程的情況下輸送黏性較大的液體。在油庫中,往復盾構機頂管專用泵泵的主要用途是輸送專用燃料油和潤滑油，還可以作為鍋爐給水泵或為離心泵抽真空引油、抽罐車底油等。由于往復盾構機頂管專用泵泵結構復雜，易損件多，流量有脈動，大流量時機器笨重，所以在許多場合為離心泵所代替。但在高壓力、小流量、輸送黏度大的液體，要求精確計量并要求流量隨壓力變化小的情況下仍采用各種型式的往復盾構機頂管專用泵泵。
一、往復盾構機頂管專用泵泵的結構和工作原理

如圖2-6所示，往復盾構機頂管專用泵泵的主要部件有泵缸、盾構機頂管專用泵、盾構機頂管專用泵桿、吸入閥和排出閥。吸入閥和排出閥均為單向閥。電動往復盾構機頂管專用泵泵通常是用曲柄連桿機構,把電動機的旋轉運動變為盾構機頂管專用泵的往復運動。當盾構機頂管專用泵向右移動時，泵缸的容積增大而形成低壓。排出閥受排出管內液體壓力作用而關閉;吸入閥受貯槽液面與泵缸內的壓差作用而打開,使液體吸入泵缸。當盾構機頂管專用泵向左移動時,由于盾構機頂管專用泵的推壓,缸內液體壓力增大,吸入閥關閉，排出閥開啟,使液體排出泵缸，完成一個工作循環。盾構機頂管專用泵在泵缸內兩端間移動的距離，稱為行程。
    盾構機頂管專用泵在泵缸內往復一次只有一次排液的泵，稱為單作用泵，如圖2-6所示。當盾構機頂管專用泵兩面都作用，即一面吸入，另一面就排出,這時一個往復行程內完成兩次吸排過程.其流量約為單作用泵的兩倍.稱為雙作用泵,如圖2-7所示。
    往復盾構機頂管專用泵泵啟動前不用灌泵，能自動吸入液體,即有自吸能力。但實際操作中，仍希望在啟動時泵缸內有液體，這樣不僅可以立即吸、排液體,而且可避免盾構機頂管專用泵在泵缸內干摩擦，以減少磨損。往復盾構機頂管專用泵泵的轉速(即往復頻率)對泵的自吸能力有影響。若轉速太大，液體流動阻力增大，當泵缸內壓力低于液體飽和蒸氣壓時，會造成泵的抽空而失去吸液能力。因此,往復泵轉速n不能太高，一般在80~ 200r/min之間,吸入高度(安裝高度)為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.