Self-priming pumps are inherently designed to allow the pump to re-prime itself typically under lift conditions. These pumps are very effective to the end user in that they will eliminate the need for foot valves, vacuum and ejector pumps which can become clogged or be impractical to use for prolonged or remote operation. Although the pump itself is designed to accomplish this task, it Is important to understand the principle of how self-priming is achieved so that the piping system can be designed so as not to conflict with this function.
A self-priming pump, by definition, is a pump which will clear its passages of air if it becomes air bound and resume delivery of the pumpage without outside attention. To accomplish this, a charge of liquid sufficient to prime the pump must be retained in the casing (See Fig. A) or in an accessory priming chamber. When the pump starts, the rotating impeller creates a partial vacuum; air from the suction piping is then drawn into this vacuum and is entrained in the liquid drawn from the priming chamber. This air-liquid mixture is then pumped into the air separation chamber (within the casing) where the air is separated from the liquid with the air being expelled out the discharge piping (Fig. B) and the liquid returning to the priming chamber. This cycle is repeated until all of the air from the suction piping has been expelled and replaced by pumpage and the prime has been established (Fig. C).

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SP self-priming pump Features
SP Non-clogging self-priming sewage pump is our latest developed product, and is suitable for the treatment project of municipal sewage and industrial sewage as well as stage treatment and concentrated treatment system of various sewages. It's known as "King of Self-priming Sewage Pump", and the most ideal new-generation sewage product.
1. Stable performance, reliable operation;
2. Rapid self-priming, high suction head;
3. Back-pull-out construction: Convenient for maintenance and troubleshooting. Daily maintenance can be performed rapidly by common head tools, saving time and labor;
4. Semi-open impeller structure and non-clogging design: Strong passing capacity. Diameter of maximum passing grain for SP-6 is 76 mm;
5. Convenient usage: The pump can be mounted high and dry at floor level, with only the suction line down in the liquid. (the pump shall be filled with water for first start).

SP self-priming pump Application
1. Rain Water and common sewage;
2. Municipal drainage project, construction site, drainage station of people's air defense system;
3. Industrial sewage of light industry, paper mill, textile, food processing plant, chemical industry, electric utility, deep mines, etc.;
4. Sewage discharge in the residential area;
5. Sewage and deposit of water purifying system;
6. Tanning industry, sewage of slaughter house, fish breeding in the river and pond;
7. Wine and sugar industry;
8. Sewage discharge not having strong corrosiveness but seriously polluted.

SP self-priming pump Operating Limits
1. Liquid temperature: 0 degree---40 degree, medium density 1.2χ 10 3 kg /m 3, PH5 -- 9;
2. Volume ratio of solids in the medium <2%;
3. Diameter of maximum grain: SP-3 63mm; SP-4/SP-6 76mm;
4. Ambient temperature: < 40 degree;
5. Altitude: Max. 1000m;
6. Max. Working pressuresee Performance Curve;
7. Max. Suction head: See Performance Table.