The metering pump is a pump designed to measure the delivery of liquid. Most metering pumps use plunger pumps and diaphragm pumps, and are also useful for gear pumps because they can maintain constant flow regardless of discharge pressure. The metering pump has two kinds of adjustable and non-adjustable flow, the applicability of the former is wider. The flow is mainly adjusted by changing the length of the stroke, for example by changing the crank radius, the distance between the trailing point of the plunger return and the plunger rod and the crosshead, and by adjusting the number of reciprocations or by adjusting the flow rate in two ways. Although the stroke length can be adjusted from zero to the maximum, but in order to ensure the measurement accuracy, are generally limited to 30 to 100% range.
The metering accuracy of the metering pump is the accuracy of the flow reproducibility, usually calculated by the maximum flow rate. In the range of 10 to 100%, the metering accuracy of the metering pump is ± 1% (the special metering pump is more accurate). The main factors that affect the measurement accuracy are the sealing of the plunger packing and the perfection of the suction and discharge valve work.
The plunger metering pump has the advantages of high measurement precision, wide adjustment range and high pressure, but there is leakage in the packing seal, which will affect the measurement accuracy of the pump after the packing is corroded and worn. This metering pump flow is generally 4 to 4000 liters / hour, the pressure is generally below 5 × 105 Pa.
The main advantage of diaphragm metering pumps is that there is no leakage and is therefore particularly suitable for applications where leakage is not allowed, such as flammable, explosive, toxic and radioactive media, and can be used to transport liquids containing solid particles. The This metering pump flow is generally below 2500 liters / hour, the pressure can be up to 35 MPa.
The metering pump can be used to complete the three functions of conveying, measuring and adjusting, thus simplifying the production process, realizing automation and semi-automation, and improving product quality. Using multiple cylinders or multiple metering pumps, several media can also be mixed into the reactor in an accurate proportion.
Dosing pumps are increasingly used in chemical, oil refining, pharmaceutical, food and nuclear industries. Metering pump efficiency is low, generally 20%, power is also very small.