A. The centrifugal pump discharge pressure
The centrifugal pump discharge pressure refers to the total pressure energy (unit: MPa) after the liquid is sent through the pump. It is an important indicator of whether the pump can complete the task of conveying liquid. The discharge pressure of the pump may affect the normal production of the user. Therefore, the discharge pressure of the pump is determined according to the needs of the actual process. According to the needs of the production process and the requirements of the manufacturer, the discharge pressure mainly has the following representation methods.
1. Normal operating pressure The pump discharge pressure required for the company to operate under normal operating conditions.
2. The maximum need to discharge pressure When the production conditions of the enterprise change, the possible discharge conditions of the pump discharge pressure may occur.
3. Rated discharge pressure The discharge pressure specified by the pump manufacturer and guaranteed. The rated discharge pressure should be equal to or greater than the normal operating pressure. For vane pumps, the discharge pressure should be at maximum flow.
4. Maximum allowable discharge pressure The pump's maximum allowable discharge pressure value determined by the pump manufacturer based on pump performance, structural strength, prime mover power, etc. The maximum allowable discharge pressure value should be greater than or equal to the maximum required discharge pressure, but should be lower than the maximum allowable working pressure of the pump pressure component.
B. The centrifugal pump head (pressure difference) H
The head of a water pump refers to the energy obtained by passing a unit of liquid through a pump. It is expressed in H, and the unit is m, that is, the height of the liquid column from which the liquid is discharged. The effective energy obtained by the unit pressure of the liquid after passing through the pump, also known as the total lift or full lift. It can also be said that the energy difference between the liquid at the outlet of the pump and the inlet is. However, it must be stated that it is only related to the performance of the pump itself, and has nothing to do with the inlet and outlet lines. The unit of the head is N·m or m liquid column height. For high-pressure pumps, the pressure difference (p2 - P1) between the pump outlet and the inlet is sometimes approximated to indicate the head size. At this time, the head H can be expressed as:
Where P1 - pump outlet pressure, Pa; P2 pump inlet pressure, Pa; p - liquid density, kg / m3; g - gravity acceleration, m / S2. The lift is the key performance parameter of the pump. According to the requirements of petroleum and chemical process and the requirements of the pump manufacturer, the following requirements are imposed on the lift of the magnetic pump.
1 Normal operation of the pump head under the normal production conditions of the pump, the pump discharge pressure and the suction pressure.
2 The maximum need for the head of the company to change the production conditions, the maximum discharge pressure that may be required (the suction pressure has not changed) when the pump lifts. The lift of the magnetic drive pump used by the enterprise should be the lift at the maximum flow required in chemical production.
3 Rated head The rated head is the head of the pump under the rated impeller diameter, rated speed, rated suction and discharge pressure. It is the head determined and guaranteed by the pump manufacturer, and the head value should be equal to or greater than the normal operating head. Generally take its value equal to the maximum required head.
4 Close the head The lift head is the head when the pump flow is zero. For the maximum limit lift of the pump, the discharge pressure under the lift is generally used to determine the maximum allowable working pressure of the pressure component such as the pump body. The head of the pump (pressure difference) is the key characteristic parameter of the pump. The pump manufacturer should provide the flow head with the pump flow as the independent variable (pressure difference curve).
