A displacement pump that pumps and increases the volume of work in a cylinder by alternately moving the piston, plunger, or diaphragm in the pump cylinder to increase or decrease the volume of the work in the cylinder. Reciprocating pump according to reciprocating components are divided into piston pumps, piston pumps and diaphragm pumps of 3 types.
The piston pump consists of a pump cylinder, a piston, a suction valve, a discharge valve and a drive mechanism. Figure 1 is a single acting electric piston pump. When the piston moves to the right, the pump cylinder working volume increases, the cylinder pressure is reduced, suction check valve is opened, the liquid into the pump cylinder; when the piston moves to the left (return trip), working cubage, cylinder pressure, suction check valve closed, open the discharge valve to discharge the liquid one-way. The piston is provided with a sealing filler to prevent the liquid from leaking to the other side of the piston. Piston pump is divided into two types of crankshaft, connecting rod transmission and steam direct action. According to the number and mode of the pump cylinder, the piston pump is divided into single cylinder, double cylinder and multi cylinder, as well as single acting and double acting types. A single acting pump is discharged in only one direction of movement; the pump is discharged in two directions (on the direction of the trip and the return stroke). A twin or multi cylinder pump is equivalent to two or more parallel single cylinder pumps. Most of the multi cylinder pumps are single acting type. The piston pump is generally applicable to high pressure (up to 7 MPa) and smaller flow (100 meters / 3 below), crankshaft driving piston pump by motor or internal combustion engine through the reduction gear drive, and by the crank (see slider crank mechanism) the rotary motion into reciprocating motion. Generally speaking, the pressure of the pump is higher than that of the steam directly, and the number of reciprocating is also large, but it can only change the number of reciprocating or stroke length by mechanical method, and the structure is more complicated. In addition, running in the case when the barrier discharge pipe (such as discharge valve does not open or pipeline blockage), pump pressure and shaft power increases to the pump cylinder rupture or the motor is burnt, therefore must set the safety valve to prevent overload. The steam direct acting piston pump (Fig. 2) uses steam (and sometimes compressed air) to push the cylinder piston together so as to move together with the pump cylinder piston at the same piston rod. The pump regulates the flow by changing the opening of the steam valve (i.e., by changing the amount of steam in it). Flow can be adjusted from maximum to zero. The pressure of the pump can also be changed by varying the pressure of the steam inlet. When the steam pressure is not enough to overcome the external resistance, the pump will stop automatically, so there will be no risk of overload. The steam direct acting piston pump is designed only as a single cylinder, double acting or double cylinder. Steam direct acting pump, sometimes flow up to 460 meters 3 / time.
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