Before the horizontal single-stage centrifugal pump is started, it must first be filled with water to discharge the air in the pump casing. It can be known from the working principle of the centrifugal pump that when the impeller rotates, the water is thrown to the outer edge of the impeller by centrifugal force, a vacuum is formed at the center of the impeller, and the water is sucked in, forming the continuous working process of the pump. If the pump body is not filled with water, but with air when it is started, since the density of air is much smaller than that of water, the centrifugal force generated by the air will be much smaller than that of water when the impeller rotates at the same speed. This will accumulate in the center of the impeller, so that the center of the impeller cannot form a sufficient vacuum, hinder the suction of water, and affect the formation of the continuous working process of the pump. Therefore, before the horizontal single-stage centrifugal pump is started, it must first be filled with water and the air in the pump body must be emptied, so as to maintain the normal operation of the pump.

Before the horizontal single-stage centrifugal pump is started, the water pump and the water inlet pipe should be filled with water, otherwise the pump will not be able to pump water. The horizontal single-stage centrifugal pump does not produce water after it is started, which is often due to the fact that the air in the pump is not drained and the water is not filled.
Before starting the pump, fill the tank with water to seal it. After the water pump is started, the water pump enters the water from the vacuum tank. Due to the drop of the water level in the water tank, a certain vacuum is formed in the water tank. The pump starts to run normally. This water filling method has the following advantages: small hydraulic loss, high pumping station efficiency, low labor intensity of technicians, easy start-up, and the realization of automatic control of the pump unit.
There are two main water filling methods before the horizontal single-stage centrifugal pump is started: one is to use the assembled bottom valve to fill the water. The bottom valve is a one-way valve and is installed at the inlet of the water inlet pipe. The loss is relatively large, which affects the efficiency of the pump; the other is to fill with water without a bottom valve. The great advantage of this method is energy saving, which can save 10% to 15% of energy compared with the pump station with a bottom valve.