Horizontal split-case pumps are commonly used water pumps. During operation, the following issues may occur, causing the pump to fail to function normally:
I. Causes of No Water Discharge from Horizontal Split-Case Pumps
- Insufficient water filling before starting the horizontal split-case pump. Sometimes, it seems that the filled water has overflowed from the air vent, but the pump shaft is not rotated to completely expel the air, leaving a small amount of air trapped in the suction pipe or pump body.
- The horizontal section of the suction pipe connected to the horizontal split-case pump should have a downward slope of more than 0.5% against the water flow direction, with the end connected to the pump inlet being the highest point (it should not be completely horizontal). If the pipe tilts upward, air will accumulate inside the suction pipe, reducing the vacuum degree in the pipe and the pump, thus affecting water suction.
- The packing of the horizontal split-case pump is worn due to long-term use or is too loose. This causes 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 pump through these gaps, impairing water lifting.
- The suction pipe is submerged underwater for a long time, leading to corrosion and holes in the pipe wall. After the pump starts working, the water level drops continuously. When these holes are exposed above the water surface, air enters the suction pipe through the holes.
- Cracks in the elbow of the suction pipe or tiny gaps at the connection between the suction pipe and the horizontal split-case pump may allow air to enter the suction pipe.
II.Causes of Low Pump Speed (Note: The original text omitted the "II." heading, which is supplemented here for logical consistency)
- Human factors: Some users randomly replace the original motor with another one when the original motor is damaged. This results in low flow rate, low head, or even no water discharge.
- Mechanical faults of the horizontal split-case pump itself: Loosening of the locking nut between the impeller and the pump shaft, or deformation/bending of the pump shaft, causes the impeller to shift and directly rub against the pump body. Bearing damage can also reduce the pump speed.
- Improper maintenance of the prime mover: If the motor loses magnetism due to winding burnout, or if the number of winding turns, wire diameter, or wiring method is altered during maintenance, or if faults are not completely eliminated during maintenance, the pump speed may change.
III. Excessive Suction Lift of the Horizontal Split-Case Pump
In some cases, the water source is deep, or the surrounding terrain of the water source is relatively flat. However, the allowable suction lift of the horizontal split-case pump is ignored, leading to insufficient water suction or even no water suction at all. It should be noted that the vacuum degree that can be established at the pump’s suction port is limited: the suction lift under absolute vacuum is approximately 10 meters of water column, but a horizontal split-case pump cannot achieve absolute vacuum. Moreover, excessively high vacuum度 can easily cause water vaporization inside the pump, which is harmful to the pump’s operation. Therefore, each centrifugal pump has a maximum allowable suction lift, typically ranging from 3 to 8.5 meters. Never prioritize convenience and simplicity when installing a horizontal split-case pump.
IV. Excessive Resistance Loss in Inlet and Outlet Pipes
After measurement, some users find that even though the vertical distance from the reservoir/water tower to the water surface of the source is slightly less than the pump head, the water lifting volume is still small or no water is lifted. This is often because the pipeline is too long or has too many bends, resulting in excessive resistance loss of water flow in the pipeline. Generally, a 90-degree elbow causes greater resistance than a 120-degree elbow: each 90-degree elbow leads to a head loss of approximately 0.5–1 meter, and the resistance of every 20 meters of pipeline can cause a head loss of about 1 meter. In addition, some users randomly change the diameter of the pump’s inlet or outlet pipe, which also has a certain impact on the head.
V. Other Causes of Insufficient Water Lifting (Note: The original text omitted the "V." heading, which is supplemented here for logical consistency)
- The foot valve fails to open: This usually occurs when the horizontal split-case pump is left unused for too long, causing the foot valve gasket to stick. Foot valves without gaskets may rust and seize.
- The foot valve filter screen is clogged: The foot valve may be submerged in the sludge layer underwater, leading to filter screen blockage.
- Severe impeller wear: The impeller blades wear out after long-term use, affecting the pump’s performance.
- Faults or blockages in the gate valve or check valve: These issues can reduce the flow rate or even prevent water from being pumped.
- Leakage in the outlet pipe: This can also affect the water lifting volume.
