As professionals in the water pump industry, we must master not only sales and maintenance but also installation. The installation of the pump's inlet and outlet is particularly critical; improper installation can impair performance and, over time, compromise the pump's quality and shorten its service life. Today, the experts at Shanghai Shenyin Pump will outline the key considerations for installing pump inlets and outlets.
1. Horizontal sections of the inlet pipe: Installing these sections horizontally or with an upward slope causes air to accumulate inside the pipe. This reduces the vacuum level within the inlet pipe and the centrifugal pump, thereby lowering the suction lift and decreasing the water output. The correct approach is to ensure the horizontal section slopes slightly toward the water source; it should never be perfectly horizontal or tilted upwards.
2. Excessive use of elbows in the inlet pipe: Using too many elbows increases local flow resistance. Furthermore, elbows should only facilitate turns in the vertical plane; horizontal turns are not permitted, as they can lead to air accumulation.
3. Using small-diameter pipes with large-diameter centrifugal pumps: Many people believe this increases the pump's actual head (Actual Head = Total Head - Head Loss). Once the pump model is selected, the total head is fixed. Head loss stems primarily from pipeline resistance; a smaller pipe diameter creates greater resistance and, consequently, higher head loss. Therefore, reducing the pipe diameter actually lowers the pump's actual head and reduces its efficiency, rather than increasing it.
Conversely, using a large-diameter pipe with a small-diameter pump does not lower the actual head; instead, the reduced pipeline resistance lowers head loss, thereby slightly increasing the actual head. Some operators also mistakenly believe that using a large-diameter pipe with a small-diameter pump significantly increases the motor load, assuming that a larger pipe diameter exerts greater pressure from the water in the outlet pipe onto the impeller. In reality, however, liquid pressure depends solely on the head height, not on the cross-sectional area of the water pipe. Provided the head remains constant and the impeller dimensions are unchanged, the pressure exerted on the impeller remains fixed regardless of the pipe diameter. While increasing the pipe diameter reduces flow resistance—thereby increasing the flow rate and power consumption—the pump will continue to operate normally within its rated head range; furthermore, a larger diameter can reduce pipeline losses and improve pump efficiency.
4. Connecting an elbow directly to the pump inlet causes uneven flow distribution as the water enters the impeller. If the inlet pipe diameter exceeds that of the pump inlet, an eccentric reducer should be installed. The flat side of the reducer must face upward, while the sloped side faces downward; otherwise, air may accumulate, leading to reduced output, failure to prime, or knocking sounds. If the inlet pipe and pump inlet have the same diameter, a straight pipe section should be inserted between them, with a length at least two to three times the pipe diameter.
5. Installing the bottom section of an inlet pipe (equipped with a foot valve) at a non-vertical angle prevents the valve from closing properly, resulting in leakage. The correct installation method is to ensure the bottom section of the inlet pipe is vertical. If terrain constraints make vertical installation impossible, the angle between the pipe axis and the horizontal plane must be greater than 60°.
6. Incorrect intake positioning or insufficient submergence depth: If the intake of the suction pipe is not submerged deeply enough, vortices may form on the water surface around the pipe, hindering intake and reducing discharge volume. Proper installation requires a minimum submergence depth of 300–600 mm for small-to-medium pumps and 600–1000 mm for large pumps. 7. Discharge outlet positioned above the normal water level of the discharge basin: Placing the outlet above the normal water level increases the pump's required head but reduces the flow rate. If site conditions necessitate an outlet position higher than the water level, an elbow and a short pipe section should be installed to create a siphon effect, thereby effectively lowering the discharge outlet height.
We hope you have gained some useful insights from the information above regarding the installation of pump inlets and outlets.