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.