The water pump isn't pumping? Where do you usually look for the cause?

Is your Water Pump not pumping water? Where do you usually look for the cause?

Air in the inlet pipe or Pump body:
1. If the Pump wasn’t filled with enough water before starting, sometimes it seems like the water has overflowed from the air vent, but the Pump shaft hasn’t turned enough to fully expel the air, leaving some air in the inlet pipe or Pump body.
2. The horizontal section of the inlet pipe in contact with the Pump should slope downward at more than 0.5% against the reverse water flow direction, with the end connected to the Pump inlet being the highest. Don’t keep it completely level. If it curves upward, air will remain in the inlet pipe, reducing the vacuum in the pipe and Pump, affecting suction.
3. The Pump packing may have worn out from long-term use or may be too loosely pressed, causing a large amount of water to spray through the gaps between the packing and the Pump shaft sleeve. This allows external air to enter the Pump, affecting water delivery.
4. If the inlet pipe has been underwater for a long time, corrosion may create holes in the pipe wall. When the Pump operates and the water level falls, air will enter the inlet pipe through these holes once they are exposed.

Low Pump speed:
1. Human factors. Some users replace a broken original motor with another motor arbitrarily, which can result in low flow, low head, or even no water delivery.
2. Mechanical issues of the Pump. Loose impeller-to-shaft nuts, bent Pump shafts, impeller rubbing against the Pump body, or damaged bearings can all reduce Pump speed.
3. Improper engine maintenance. Electric motors that lose magnetism due to burnt windings or changes in winding turns, wire diameter, wiring methods, or unresolved faults during maintenance can also alter Pump speed.

Excessive suction lift:
Some water sources are deep or in flat terrain, and the pump’s allowable suction lift is overlooked, causing low or no water intake. Note that the vacuum a self-priming centrifugal pump can generate at the inlet is limited. Too much vacuum can vaporize the water inside, which is bad for the pump.

Excessive resistance loss in the inlet and outlet pipes:
Some users find that even if the vertical distance from the water tank or tower to the water surface is slightly less than the pump head, the water flow is still low or insufficient. This is often due to long pipes, too many bends, or high resistance loss in the flow.

Other factors:
1. Bottom valve won’t open. Usually because the pump was left idle too long, causing the bottom valve gasket to stick, or a valve without a gasket may rust and seize.
2. Bottom valve screen blockage, or sediment buildup in the submerged area blocking the filter.
3. Severe impeller wear, as long-term use wears down the blades and affects performance.
4. Gate valves or check valves malfunctioning or blocked can reduce flow or stop water delivery.
5. Leaks in the outlet pipe can also affect water delivery.