Precautions for the selection of self-priming pump

1. Types of self-priming pumps and their advantages and disadvantages in practical applications

Commonly used self-priming pumps are: self-priming self-priming pumps and self-priming pumps with diversion tanks.

Self-priming self-priming pump: refers to a centrifugal pump that can automatically pump water up without filling the suction line with water, which is called a self-priming pump.

The self-priming pump with a diversion tank is actually a combination of a water tank and an ordinary centrifugal pump, and the structure is different from that of a self-priming pump.

2. Advantages and disadvantages:

(1) The self-priming pump with diversion tank mainly covers a large area and has more preliminary design work, but it is suitable for many occasions and has high pump efficiency.

(2) The self-priming centrifugal pump system is simple in design, especially suitable for low-flow wastewater transportation occasions.

(3) Self-priming self-priming self-priming pump has many limited conditions, such as large flow, high head, complex working conditions, materials, etc., and the self-priming pump is not as selective as centrifugal pump.

(4) Compared with centrifugal pumps with the same performance parameters, the self-priming self-priming pump has lower efficiency and poor cavitation performance.

(5) Both pump types need to be filled when starting, and some manufacturers have proposed that the self-priming self-priming pump can not be filled before starting, but due to the inhalation of air and exhaust time, it will lead to a long waiting time for normal suction.

2. Precautions for the design of self-priming pumps with diversion tanks

(1) To determine the volume of the diversion tank, first determine the diameter of the inlet pipe according to the flow rate, and the volume of the diversion tank is generally 3-5 times the gas volume of the inlet pipe.

(2) The diversion tank must be kept closed after filling and does not leak, otherwise it will make the water absorption poor.

Haihua nanofiltration project, 800m3/h self-priming pump, water absorption instability occurred during the early start-up, and I thought it was a design problem at first.

(3) The inlet pipeline should be short, straight and with few elbows as much as possible to reduce the inlet resistance and ensure the vacuum level.

(4) Diversion tank design type:

3. Precautions for the design of self-priming self-priming pumps

(1) The inlet pipeline should be short, straight and with fewer elbows to reduce the inlet resistance and ensure the vacuum sucking.

(2) The diameter of the inlet pipeline is generally consistent with the diameter of the pump, and it can only be larger by one specification at most, otherwise it will increase the air volume of the inlet pump and cause difficulty in water absorption;

(3) When the water in the suction pipeline contains dissolved gas, it will escape due to the decrease of pressure in the pipeline, and if there is gas accumulation somewhere in the suction pipeline, an air bag will be formed, which will affect the water passing capacity of the pipeline. In severe cases, it will destroy the vacuum water absorption. In order to make the pump can drain the gas in the suction line in time. The suction pipe should have a slope that rises continuously along the water flow. and i≥0.005. make the gas in the pipe be discharged from the top of the pump casing at the inlet of the water pump. The installation and laying of the suction pipe of the self-priming pump should avoid the formation of air bags in the pipeline.

(4) The design flow rate of the suction pipe of the self-priming pump is generally as follows: when the diameter of the suction pipe is less than 250mm, the flow rate is 1.0~1.2m/s; When the diameter of the suction pipe is 250~1000mm, the flow rate is 1.2~1.6m/s; When the diameter of the suction pipe is greater than 1000mm, the flow rate is 1.5~2.0m/s.

4. the self-priming pump can not suck up the water reasons and solutions

(1) Because the suction pipe of the self-priming pump is not tightly sealed, the self-priming pump has been in the state of pumping air, so the self-priming pump cannot suck up water.

Solution: It is to check the inlet pipeline seal of the self-priming pump, repair the air leakage point, such as the weld, the pipe joint and other places that are suspected of possible air leakage, for example, you can use the operation for about 5 minutes to stop the machine close to the pipeline and listen to whether there is a suction sound.

(2) The self-priming pump that has been used for a period of time will be the reason why the self-priming pump cannot suck up water due to corrosion or wear and leakage of mechanical seals.

Solution: Replace the damaged part with a new one.

(3) Due to the large amount of debris in the conveyed liquid, the pipeline or the bottom valve or even the pump body is blocked, which will also be the reason why the self-priming pump cannot suck up the water.

Solution: Find the specific blockage point and clean up the debris to solve the problem.

(4) Due to the unreasonable installation of the inlet pipeline, such as the number of elbows is too large, the number of elbows should be controlled as much as possible in 1-2 or 2 elbows, and the elbow of 45 degrees should be used as much as possible.

(5) After the self-priming pump sucks up the water for the first time, it must be filled with water to suck it up for the second time, indicating that there is air entering the pump body, for example, the outlet pipe of the self-priming pump is not equipped with a check valve, because the outlet is connected to the atmosphere, there will be water backflow after the pump is stopped, and the air will be sucked into the pump body, because there is air entering, so the next start also needs to fill and exhaust to suck the water up.

The solution to the problem of this self-priming pump not being able to suck up water: installing a check valve at the outlet can solve the problem.

(6) In the actual installation and use of the self-priming pump, the suction height exceeds the allowable suction height of the self-priming pump.

It is recommended to replace the self-priming pump with a higher self-priming height, or to solve the problem by increasing the start-stop pump level.