500QZB Submersible Axial Flow Pump

Tianjin Zhijiang Pump Industry500QZBComplete Range of Submersible Axial Flow Pump Models

Zhijiang Pump Industry500QZBSubmersible Axial Flow PumpSpecial Operating Conditions

(1) In cases where the well contains a high sand content, special attention must be paid during pump operation. The pump should continue running until the water in the well shows no turbidity before it can be stopped. Otherwise, sand particles will settle on the rear cover plate of the impeller, and the pump may fail to start again. Further operation under such conditions could burn out the motor. This situation often occurs when well cleaning is incomplete in the market. In such cases, the motor must be allowed to run continuously until the water in the well is clear before shutdown.

(2) The insulation resistance of the stator winding of the submersible motor is zero, but the electric pump can still operate normally.

This phenomenon can only occur in star-connected submersible motors. If the star point of the motor is poorly insulated, the stator winding's insulation resistance to ground becomes zero. Although the motor appears to be grounded, no abnormal phenomena such as increased motor current occur, and the pump continues to operate normally. However, this does not meet the requirements of electrical safety regulations. In such cases, the pump should be lifted out of the well for disassembly and inspection. The star point should be reinsulated to restore the insulation resistance of the motor stator winding.

The operation of an axial flow pump is based on the lift theory of airfoils in aerodynamics. Its blades have a cross-section similar to that of an airfoil, generally referred to as an airfoil-shaped blade. Wind tunnel tests on airfoils show that when fluid flows around an airfoil, it separates at point A at the leading edge into two streams. These streams pass over the upper surface (i.e., the working surface of the axial flow pump blade) and the lower surface (the back surface of the axial flow pump blade) of the airfoil, respectively, and then converge at point B at the trailing edge. Since the path along the lower surface of the airfoil is longer than that along the upper surface, the fluid velocity along the lower surface is greater than that along the upper surface. Correspondingly, the pressure on the lower surface will be lower than that on the upper surface, resulting in a downward force P exerted by the fluid on the airfoil. Similarly, the airfoil exerts an equal and opposite reaction force P' on the fluid, directed upward.

When blades with an airfoil cross-section rotate at high speed in water, the water flow relative to the blades generates rapid circulation. As described above, the blades exert a force P on the water.

Under this force, the water is pressurized and lifted to a certain height. From the derivation of the basic equation of centrifugal pumps, it is known that regardless of the blade shape, the form of the equation depends only on the momentum moment at the inlet and outlet. That is, regardless of the internal flow conditions of the impeller, energy transfer is determined by the velocity quadrilaterals at the inlet and outlet. Therefore, this basic equation applies not only to centrifugal pumps but also to axial flow pumps, mixed flow pumps, and all other vane pumps, hence it is also called the basic equation of vane pumps.

Zhijiang Pump Industry500QZBSubmersible Axial Flow PumpPerformance Characteristics

Compared to centrifugal pumps, axial flow pumps have the following performance characteristics:

(1) The head increases sharply as the flow rate decreases. The Q-H curve drops steeply and has an inflection point, as shown in Figure 2-77. The main reason is that at low flow rates, backflow occurs at the inlet and outlet of the impeller blades, causing the water to receive energy multiple times, similar to a multi-stage pressurization state, resulting in a sharp increase in head. Additionally, backflow increases hydraulic resistance losses, leading to an increase in shaft power. The no-load head is typically about 1.5-2 times the head at the design operating point.

(2) The Q-N curve is also a steeply descending curve. When Q=0 (with the discharge valve closed), the shaft power N₀ = (1.2 to 1.4) N_d, where N_d is the shaft power at the design operating point. Therefore, when starting an axial flow pump, the motor should be started with the valve fully open, generally referred to as "open-valve starting."

(3) The Q-N curve is hump-shaped, meaning the range of high-efficiency operation is very narrow. Efficiency drops rapidly even with slight deviations from the design operating point. Due to this characteristic, flow regulation using a valve is unfavorable for axial flow pumps. Typically, only the blade angle β is adjusted to change the performance curve, a method known as variable-angle regulation. For large fully adjustable axial flow pumps, to reduce starting power, the blade angle β is usually reduced before starting and gradually increased after startup. This approach fully utilizes the characteristics of fully adjustable axial flow pumps. Figure 2-78 shows the universal characteristic curve of an axial flow pump, which includes performance curves, iso-efficiency curves, and iso-power curves for different blade angles β at a fixed speed. This graph allows for easy selection of the appropriate blade angle based on required operating parameters or for pump selection.

(4) In pump catalogs, the suction performance of axial flow pumps is generally expressed using the net positive suction head (NPSH) value, Δh_sv. The NPSH value is determined through cavitation tests by the pump manufacturer. Axial flow pumps typically require a larger NPSH, resulting in a smaller maximum allowable suction lift. Sometimes, the impeller needs to be submerged at a certain depth, resulting in a negative installation height. To ensure no cavitation occurs during operation, careful consideration must be given to the inlet conditions of the axial flow pump (including submergence depth of the suction inlet, shape of the suction flow passage, etc.), the deviation of the actual operating point from the design operating point, the manufacturing quality of the impeller blades, and the installation quality of the pump.

Zhijiang Pump Industry500QZBSubmersible Axial Flow Pump and QHB-type mixed flow submersible electric pumps are upgraded replacements for traditional pump-motor units. The motor driving the pump is a dry, fully enclosed submersible three-phase asynchronous motor. These submersible electric pumps can operate submerged in water for extended periods, offering a series of unparalleled advantages over traditional units.

The above models are for illustrative purposes only. Online prices do not represent actual selling prices. For specific prices, please inquire by phone.