Types and characteristics of metering pumps

According to the structural type of the hydraulic end of the metering pump, the metering pump is often divided into plunger type, hydraulic diaphragm type, mechanical diaphragm type and electromagnetic metering pump.

1. Plunger metering pump

The structure of the plunger metering pump is basically the same as that of the ordinary reciprocating pump. Its hydraulic end is composed of hydraulic cylinder, plunger, suction and discharge valves, sealing packing, etc. in addition to meeting the design requirements of the hydraulic end of the ordinary reciprocating pump, the suction valve, discharge valve, sealing and other components affecting the metering accuracy of the pump shall be carefully designed and selected.

Features of plunger metering pump:

(1) Lower price;

(2) The flow can reach 76m / h, the flow is in the range of 10% ~ 100%, the metering accuracy can reach ± 1%, and the maximum pressure can reach 350Mpa. When the outlet pressure changes, the flow is almost unchanged;

(3) It can transport high viscosity media and is not suitable for transporting corrosive slurry and dangerous chemicals;

(4) The shaft seal is a packing seal. If there is leakage, the packing needs to be adjusted periodically. The packing and plunger are easy to wear, so the packing ring needs to be pressure washed and discharged;

(5) No safety relief device.

2. Hydraulic diaphragm metering pump

Hydraulic diaphragm metering pump is the most widely used metering pump in industrial production. The hydraulic diaphragm metering pump is usually called diaphragm metering pump. Figure 3 shows a single diaphragm metering pump. A layer of diaphragm is installed at the front end of the plunger (the plunger is not in contact with the diaphragm) to separate the hydraulic end into infusion chamber and hydraulic chamber. The infusion chamber is connected with the pump suction and discharge valves. The hydraulic chamber is filled with hydraulic oil (light oil) and is connected with the hydraulic oil tank (makeup oil tank) at the upper end of the pump body. When the plunger moves back and forth, the pressure is transmitted to the diaphragm through the hydraulic oil, and the front and rear deflection deformation causes the change of volume, which plays the role of conveying liquid and meets the requirements of accurate measurement.

There are two kinds of hydraulic diaphragm metering pumps: single diaphragm and double diaphragm. Once the diaphragm of single diaphragm metering pump is broken, the transmitted liquid is mixed with hydraulic oil, which is prone to accidents for some media. The double diaphragm pump fills the inert liquid between the two diaphragms, such as soft water, alcohol, aromatic hydrocarbon and fatty hydrocarbon, and requires that the inert liquid will not cause harmful reaction when mixed with the transmitted medium or hydraulic oil. When one of the diaphragms breaks, it can give an alarm in time by means of pressure gauge, acousto-optic device or chemical inspection. When the conveying liquid is not allowed to contact with any inert liquid, vacuum can be generally used between the two diaphragms.

SH / T 3142-2004 stipulates that double diaphragm metering pump shall be used for hazardous media, harmful media or media that will react with hydraulic oil. In order to increase the reliability of the pump, double diaphragm metering pump is also recommended for other occasions.

Features of hydraulic diaphragm metering pump:

(1) No dynamic seal, no leakage, safety relief device and simple maintenance;

(2) The outlet pressure can reach 100MPa; within the range of 10:1 regulation ratio, the measurement accuracy can reach ± 1%;

(3) The price is high

3. Mechanical diaphragm metering pump

The diaphragm of the mechanical diaphragm metering pump is connected with the plunger mechanism without hydraulic oil system. The front and rear movement of the plunger directly drives the front and rear deflection and deformation of the diaphragm, as shown in Figure 4. Since the diaphragm bears the pressure on the medium side, the maximum discharge pressure of the mechanical diaphragm pump generally does not exceed 1.2MPa.

Characteristics of mechanical diaphragm metering pump:

(1) Lower price;

(2) No dynamic seal and no leakage;

(3) It can transport high viscosity media, abrasive slurry and dangerous chemicals;

(4) The diaphragm bears high stress and its service life is low;

(5) The outlet pressure is below 2MPa, and the measurement accuracy is ± 2%;

(6) No safety relief device.

4. Electromagnetic metering pump

The electromagnetic drive technology of metering pump breaks the structural form that the motor is used as the prime mover and the gear and crank connecting rod are used as the transmission mechanism in the traditional design. The electronic control circuit is used to generate electromagnetic pulse, the electromagnetic force of the energized solenoid coil is used to drive the plunger to move back and forth in a straight line, and the stroke rate is used to adjust and control the flow. However, due to technical reasons, the power of electromagnetic metering pump is still very small.

Features of electromagnetic metering pump:

(1) Low price;

(2) No dynamic seal and no leakage;

(3) Small volume, light weight and convenient operation;

(4) It is suitable for micro dosing systems such as laboratory, water treatment, swimming pool, vehicle cleaning, small tower and reverse osmosis water treatment system