The axial flow pump is a pump that transfers the liquid in the axial direction by the force exerted by the blades of the rotating impeller on the liquid. There are vertical, horizontal, inclined and tubular types.
It is assumed that the wing is suspended in the fluid, and when the fluid flows at a certain speed, a negative pressure occurs on the airfoil surface, and a positive pressure occurs on the wing back. The magnitude of the positive and negative pressures is related to the wing shape and the angle of attack (the inclination of the wing back to the direction of the liquid flow) and the magnitude of the fluid velocity.
If the fluid does not move and the wing moves in the fluid at equal speed, the wing back and airfoil are subjected to the same positive and negative pressure as before, that is, the airfoil (above the wing) is negative pressure, and the wing back is positive pressure. The wing will gain lift under this pressure.
If the airfoil-shaped blade is fixed on the rotating shaft, the propeller is formed and it can not be moved in the axial direction. When the rotating shaft rotates at a high speed, the airfoil (lower side of the propeller) has a suction effect due to the negative pressure, and the wing back has a drainage effect due to the positive pressure, which causes the flow of the liquid (or gas).
The axial flow pump impeller is equipped with 2 to 7 blades and rotates in a circular tubular pump casing. The pump casing on the upper part of the impeller is provided with fixed vanes to eliminate the rotational movement of the liquid, to make it move axially, and to convert the kinetic energy of the rotary motion into pressure energy.
Axial pumps are usually single-stage and a few are made in two-stage. The capacity is in wide range of 1800000-3600000m³/h and the head is usually less than 20 meters. The axial flow pump is generally vertical, the impeller is submerged under water, and there is also a horizontal or inclined axial flow pump.
When the impeller installation position of the small axial flow pump is higher than the water surface, it needs to be started by the vacuum pump exhaust water. The blades of the axial flow pump are of fixed and adjustable construction. The working conditions of the large axial flow pump (mainly the flow rate) often need to be changed greatly during operation. Adjusting the installation angle of the blade enables the pump to operate in a high efficiency zone under different working conditions.
The blade mounting angle of a small pump is generally fixed. The axial flow pump is the one with the highest number of revolutions in the power pump, and the specific number of revolutions is 500 to 1600. The pump flow-lift, flow-shaft power characteristic curve is steep in the small flow area, so it should be avoided in this unstable small flow area. The axial pump has the highest shaft power at zero flow, so the pump valve must be opened before the start to reduce the starting power.
The axial flow pump is mainly suitable for low lift and large flow situations, such as irrigation, drainage, dock drainage, water level adjustment of canal locks, or large circulating water pump for power plants. The axial pump with a high lift (made in two stages if necessary) can be used for water jet propulsion of shallow water vessels.