Analysis of the reasons why the water pump does not deliver water:
Air in the suction pipe or inside the pump body
(1) The water pump was not fully primed with water before startup. Sometimes, it may appear that the water has overflowed from the vent hole, but the pump shaft was not rotated to completely expel the air, leaving some air trapped in the suction pipe or the pump body.
(2) The horizontal section of the inlet pipe connected to the water pump should have a downward slope of more than 0.5% in the reverse direction of the water flow, with the end connected to the pump inlet being the highest point. It should not be perfectly level. If it tilts upward, air will remain in the inlet pipe, reducing the vacuum level in the pipe and the pump, which affects water intake.
(3) The packing of the water pump may have worn out after long-term use or may be too loose, causing a large amount of water to spray out from the gap between the packing and the pump shaft sleeve. As a result, external air enters the interior of the pump through these gaps, affecting the water delivery.