Self-priming pumps belong to self-priming centrifugal pumps. They have the advantages of compact structure, easy operation, stable operation, easy maintenance, high efficiency, long service life, and strong self-priming ability. The pipeline does not need to install a bottom valve. Before operation, only a fixed amount of liquid needs to be stored in the pump body. Different liquids can use different materials of self-priming pumps.
The self-priming of self-priming pumps refers to starting the pump without filling the suction pipe with water (but there must be enough water in the pump body). It has the function of automatically excluding air from the suction pipe, and it enters normal operation after a short period of operation. Self-priming pumps must be filled with enough water before initial start-up, and then they can enter normal operation when started by the water left in the pump body.
Self-priming pumps are classified into the following categories according to their structure and working principles: air-liquid mixing (internal mixing, external mixing); water-ring self-priming pump; jet (water jet, gas jet).
The performance comparison of several self-priming pumps is as follows:
The self-priming efficiency of internal mixing self-priming pump is relatively high, with low manufacturing cost, long self-priming time, self-priming height lower than 10 meters, and long service life.
The efficiency of external mixing self-priming pump is relatively low, with medium manufacturing cost, short self-priming time, self-priming height lower than 10 meters, and long service life.
The pump efficiency of water-ring self-priming pump is high, with high manufacturing cost, short self-priming time, self-priming height lower than 10 meters, and relatively short service life.
The pump efficiency of jet self-priming pump is low, with high manufacturing cost, short self-priming time, self-priming height can be higher than 10 meters, and long service life.
Due to the low liquid level, the self-priming pump needs to first draw the pipeline into a negative pressure state before pumping the water. Therefore, the installation and layout of the suction pipe of the self-priming pump should follow the following self-priming pump installation specifications:
In order to prevent the self-priming pump suction pipe from leaking air, the suction pipe must be completely sealed and no air can be sucked in. The suction pipe of the self-priming pump usually uses steel pipes, and the joints are connected by welding or flange.
When the water in the suction pipe contains dissolved gas, it will overflow due to the decrease of pressure in the pipeline. If there is accumulated gas in the suction pipe, it will form an airbag and affect the water flow capacity of the pipeline. In order to enable the water pump to timely discharge the gas in the suction pipe, the suction pipe should have a continuous slope along the direction of water flow, and i≥0.005, so that the gas in the pipeline can be discharged from the top of the pump casing at the entrance of the water pump.
The installation and laying of the suction pipe of self-priming pump should avoid the formation of an airbag inside the pipeline.