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Before starting a centrifugal pump (other than self-priming pumps), the pump itself and the inlet pipe must be filled with water; otherwise, the pump cannot lift water. When a centrifugal pump does not discharge water after starting, it is often because the air in the pump has not been completely removed and the pump is not filled with water. There are mainly two methods for filling water before startup: one is to use a bottom valve for filling, where the bottom valve is a one-way valve installed at the inlet of the water intake pipe. The disadvantage of this method is that it results in significant head loss due to the bottom valve, which affects the efficiency of the pump. The other method is filling without a bottom valve, and its greatest advantage is energy savings – it can save 10% to 15% compared to pump stations that use bottom valves. The following introduces several methods for filling centrifugal pumps, for users to choose from when operating the pumps. ■The self-water-introduction method: For pump stations that use semi-submerged pump houses (i.e., those where both the inlet pipe and the top of the pumps are below the water level of the inlet tank), water can be introduced into the pumps automatically, without the need for manual water filling. The disadvantage of this type of pumping station is that it does not make full use of the water suction capacity of the pumps. Additionally, lowering the installation height of the pumps increases the amount of work required for foundation excavation, and it also makes operation and management more complicated. However, its advantages are evident as well: it facilitates the automation of the pumping station and improves efficiency. ■The manual water filling method: For small pumping stations with an inlet pipe diameter of less than 300 mm, a bottom valve is usually installed at the inlet of the pipe. In such cases, the manual water filling method is generally employed, which involves filling water through a special filling and venting hole located on the upper part of the pump casing, using a filling funnel (or an inverted ordinary bottle with its bottom removed). For small pump stations with an inlet pipe diameter of less than 300 mm, a foot valve is usually installed at the inlet of the inlet pipe; it is also possible to fill the pump from the outlet pipe of the water pump (in pump stations where the outlet pipe is short). Since no additional water filling equipment needs to be purchased, this method of water filling is quite common in current small rural pumping stations. For small pumping stations that do not have bottom valves or check valves and have short pipelines, it is also possible to start the pump while filling it with water from the outlet pipe, thereby gradually removing the air from the pump and the pipelines. Usually, after a few minutes of continuous water filling, the pump can operate normally for pumping water. ■The vacuum tank water filling method can be used for small pumping stations that do not have bottom valves. The vacuum water tank is a closed-type tank welded from sheet iron; its volume must be at least three times that of the inlet pipe. The tank should be installed as close to the pump as possible, and the bottom of the tank should be slightly lower than the pump’s axis. The height of a vacuum water tank is generally twice the diameter of the tank. Before starting the water pump, fill the water tank with water to ensure it is sealed. After the water pump is started, it draws water in from the vacuum tank. As the water level in the tank drops, a certain vacuum is created within it; under the effect of atmospheric pressure, the water in the inlet pool enters the tank through the inlet pipes, thus establishing a water circulation that allows the water pump to operate properly. ■Jet pump water filling method: When a diesel engine is used to drive a water pump for pumping water, the exhaust gas discharged from the diesel engine can be directed into a jet ejector connected to the top of the water pump, thereby evacuating air and filling the pump with water. This eliminates the need for a foot valve in the water pump. When the water pump starts, close the valve cover connected to the handle; exhaust gas is ejected from the jetter, and air in the pump is drawn out through the connecting pipe. After filling with water, open the valve cover and close the control valve. The advantages of this water filling method are, first, full utilization of the power engine, and second, improved efficiency of the pumping station. ■The self-suspended water filling method utilizes the difference in specific weights of water and air, and is achieved through the principle of \"water-air displacement\". This method can remove the bottom valve of the water pump. First, design a ventilation tank with an appropriate capacity; such tanks are usually made of plastic or thin iron sheet, and their cost is only half that of the bottom valve. Then, the air exchange tank is placed at the water pump’s inlet, forming a single unit together with the water pump and the pipelines. At the same time, a ventilation control valve is installed in the ventilation duct between the ventilation tank and the water pump. When filling with water, first fill the ventilation tank with water, then seal it with a lid, and finally open the ventilation valve. Once ventilation is complete, close the ventilation valve; some water will remain suspended in the inlet pipe. By repeating this process several times, all the air will be expelled, and the water inlet pipe will be filled with water. At this point, the water pump can be started to carry out pumping operations. Before shutting down, as long as the gate valve is closed first before shutting down the machine, the water flow will not reverse. No need to refill water next time it’s started up. The advantage of this water-filling method is that the ventilation tank is inexpensive, easy to manufacture, requires less labor, and saves energy. ■The water filling method using a vacuum pump is a commonly used water filling device for large and medium-sized pumping stations with inlet pipe diameters greater than 300 mm, or for pumping stations that require a high level of automation. It is assembled from vacuum pumps and other equipment, and the vacuum pumps commonly used in irrigation stations are mostly water ring vacuum pumps. An eccentric toothed impeller is installed within the cylindrical pump casing of the water ring vacuum pump. The pump casing is filled with circulating water; during vacuum pumping, the impeller rotates, and under the effect of centrifugal force, the circulating water in the pump casing is flung around the impeller, forming a rotating water ring on the inner wall of the pump casing. Furthermore, since the impeller is mounted eccentrically within the pump casing, the size of the space formed between the water ring and the toothed blades varies. When the impeller rotates clockwise, the space between the two blades on its right side gradually increases. Under sealed conditions, as the volume of air increases, the pressure decreases, creating a vacuum. The air in the water pump and pipelines enters the vacuum pump through the suction pipe and is drawn into the crescent-shaped suction port on the right side of the vacuum pump’s casing. In the left side of the vacuum pump impeller, the space between the two blades gradually decreases; as a result, the air is compressed and the pressure rises. Eventually, this compressed air is discharged from the crescent-shaped exhaust port on the left side of the vacuum pump pump casing, entering the water-gas separation tank where the circulated water is separated before it can be reused. As the impeller keeps rotating, the vacuum pump continuously draws in and expels air, eventually filling the water pump with water. ■The manual pump water-filling method: As a type of reciprocating positive displacement pump, manual pumps are widely used in rural areas of China. Farmers can utilize their own manual pumps as vacuum pumps to fill centrifugal pumps with water; this method is both convenient and cost-effective. *A common usage is to install a manual pump on the suction port of the centrifugal pump or near the water inlet pipeline of the pump, in order to draw in air and water. This serves as a tool for filling the centrifugal pump when it is started, thereby eliminating the need for a bottom valve in the water inlet pipeline, reducing energy loss, and improving the efficiency of the pump system. Top 10 Brands of Magnetic Pumping Systems ■ Self-priming method: For pump houses that are semi-submerged (that is, where both the inlet pipe and the top of the pump are below the water level of the inlet tank), water can be drawn into the pump automatically, without the need for manual priming. The disadvantage of this type of pumping station is that it does not make full use of the water suction capacity of the pumps. Additionally, lowering the installation height of the pumps increases the amount of work required for foundation excavation, and it also makes operation and management more difficult. However, its advantages are evident as well: it facilitates the automation of the pumping station and improves efficiency. ■The self-suspended water filling method utilizes the difference in specific weights of water and air, and is achieved through the principle of \"water-air displacement\". This method can remove the bottom valve of the water pump. First, design a ventilation tank with an appropriate capacity; such tanks are usually made of plastic or thin iron sheet, and their cost is only half that of the bottom valve. Then, the air exchange tank is placed at the water pump’s inlet, forming a connected system with the water pump and the pipelines. At the same time, a ventilation control valve is installed in the ventilation duct between the ventilation tank and the water pump. When filling with water, first fill the ventilation tank with water, then seal it with a lid, and finally open the ventilation valve. After ventilation is complete, close the ventilation valve, and some of the water will remain suspended in the inlet pipe. By repeating this process several times, all the air will be expelled, and the water inlet pipe will be filled with water. At this point, the water pump can be started to carry out pumping operations. Before shutting down, as long as the gate valve is closed first before shutting down the machine, the water flow will not reverse. No need to refill water next time it’s started up. The advantage of this water-filling method is that the ventilation tank is inexpensive, easy to manufacture, requires less labor, and saves energy. ■The water filling method using a vacuum pump is a commonly used water filling device for large and medium-sized pumping stations with inlet pipe diameters greater than 300 mm, or for pumping stations that require a high level of automation. It is assembled from vacuum pumps and other equipment, and the vacuum pumps commonly used in irrigation stations are mostly water ring vacuum pumps. An eccentric toothed impeller is installed within the cylindrical pump casing of the water ring vacuum pump. Circulating water is filled inside the pump casing. During vacuuming, the impeller rotates; under the action of centrifugal force, the circulating water in the pump casing is flung to the surroundings of the impeller, forming a rotating water ring along the inner wall of the pump casing. Furthermore, since the impeller is mounted eccentrically within the pump casing, the size of the space formed between the water ring and the toothed blades varies. When the impeller rotates clockwise, the space between the two blades on its right side gradually increases. Under sealed conditions, as the volume of air increases, the pressure decreases, creating a vacuum. The air in the water pump and pipelines enters the vacuum pump through the suction pipe, into the crescent-shaped suction port on the right side of the vacuum pump’s casing. In the left side of the vacuum pump’s casing, the space between the two blades gradually decreases; as a result, the air is compressed and the pressure rises. This compressed air is then discharged from the vacuum pump through the crescent-shaped exhaust port on the left side, entering the water-gas separation tank where the circulated water is separated before it can be reused. As the impeller keeps rotating, the vacuum pump continuously draws in and expels air, eventually filling the water pump with water.