First, the concept and classification of self-priming pumps: 1, self-priming pump is not required in the suction pipe filled with water can automatically pump up the water pump called self-priming pump. Pump most of the internal combustion engine and supporting, mounted on a mobile car, suitable for field operations. 2, self-priming pump structure type is divided into two types: external mixed self-priming pump and self-priming pump. Second, the working principle of self-priming pump: 1, outside the mixed self-priming pump working principle is: before the start of the pump filled with water in the pump housing (or the pump itself has water). After the start of high-speed rotation of the impeller so that the impeller channel flow of water to the volute, then the entrance to form a vacuum, the inlet valve against the open, the suction pipe into the air within the pump and reach the outer edge of the impeller channel. On the other hand, the water drained by the impeller into the gas-water separation chamber flows back to the outer edge of the impeller through the left and right return holes. The water flowing back from the left backwater hole is directed to the impeller channel under pressure difference and gravity and is crushed by the impeller. After mixing with the air from the suction pipe, it is thrown to the volute and flows in the direction of rotation. Then merge with the water from the right backwater hole and flow down the volute. As the liquid in the volute continuously impact cascades, constantly being crushed by the impeller, with strong air mixing, generating gas and water mixture, and continue to flow so that gas and water can not be separated. The mixture is peeled off the tongue at the volute outlet and enters the separation chamber along the stub tube. The air in the separation chamber is separated and drained by the outlet pipe, while the water is still flowing back and forth to the outer edge of the impeller through the return holes and mixed with the air in the suction pipe. So repeated cycles, and gradually sucked into the air exhaust pipe, so that water into the pump to complete the process of self-absorption. 2, within the self-priming pump, working principle and external mixed self-priming pump the same, the difference is that the return water does not flow to the outer edge of the impeller, and flow to the impeller entrance. Internal hybrid self-priming pump at start-up, to open the back of the impeller before the return valve, so that the liquid pump back to the impeller inlet. The water is mixed with the air from the suction pipe under the action of high speed rotation of the impeller to form a gas-water mixture to be discharged to the separation chamber. Here the air is drained and the water returns from the return valve to the impeller entrance. So repeated until the air exhausted, sucked in water. Self-priming pump self-priming height, and the impeller seal before the gap, the number of pumps, separation chamber liquid level and other factors. The smaller impeller seal clearance, the greater the self-priming height, generally taken as 0.3 to 0.5 mm; in the gap increases, in addition to self-priming height drop, the pump head, the efficiency is reduced. Pump self-priming height with the impeller circumferential speed u2 increases, but to the maximum height of self-priming, the number of revolutions increased self-priming height will not increase, this time only shorten the self-priming time; when the number of revolutions As you descend, the level of self-priming drops. The self-priming height also increases with increasing reservoir height (but not beyond the optimal reservoir height of the separation chamber), with all other conditions remaining constant. In order to better self-priming pump gas and water mixing, the impeller blade to be less, so that the blade pitch increases; and should be used semi-open impeller (or impeller channel wider impeller), so that more Easy backwater depth into the impeller cascade.
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