Relationship between the pressure and head of a positive displacement pump

There is a direct relationship between the pressure and head of positive displacement pumps. Head refers to the height to which a pump can lift liquid, while pressure refers to the force provided by the pump to overcome the resistance in the system. Specifically, the head (in meters) multiplied by the density of the liquid and the acceleration due to gravity (9.8 m/s²) gives the pressure of the pump (in pascals). Therefore, if all other conditions remain unchanged, increasing the head will result in an increase in pressure. .

Then please ask again: when selecting a volumetric pump, if the head required for transporting clean water is 50 meters, then the design pressure of the pump should be set at 0.5 MPa. But if it is used to transport sulfuric acid, should the pump’s pressure be set at 0.5*1.84=0.92 MPa? Also, should the outlet pressure value of a centrifugal pump also be head * density * 9.8? But I noticed that in the design documents, the value selected for the operating pressure of the pipes is the same as the head value; for example, if the head is 30 meters, the operating pressure is listed as 0.3 MPa, without taking into account the density of the medium. What’s the reason for this?

This post was last edited by Yu Wusheng on 2024-10-31 at 14:51. 1. The head of 30 meters specified by the design institute corresponds to a standard pressure of 0.3 MPa. 2. The design pressure of a positive displacement pump is the pressure that the structure can withstand; this rated or design pressure is not related to factors such as size, speed, head, or flow rate. It depends primarily on the sealing performance of the internal components and the structural capacity to bear loads. 3. The head generated by a positive displacement pump depends on the power of its drive motor. (Without considering the strength of the pump body and the effectiveness of its mechanical seals), theoretically, there is no upper limit to the head that a perfectly leak-free positive displacement pump can generate. 4. Positive displacement pumps do not have the concept of outlet pressure; unlike centrifugal pumps with a head of 10 meters, which eject water at the outlet as soon as a pipe is connected, even the most powerful positive displacement pumps only discharge fluid under pressure, which is generated by the presence of pipes and resistance. You think of a hand-cranked gear oil pump or a hand-cranked piston pump for firefighting – the head pressure achieved will be different when operated by a 3-year-old child, a 20-year-old teenager, or a 30kW motor.

The outlet pressure of a positive displacement pump is related to the back pressure