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Why ‘head’ and ‘pressure’ mean the same in pump?

Views: 40     Author: Site Editor     Publish Time: 2021-11-12      Origin: Site

I clearly remembered: when I participated in the Qingdao Water Exhibition in 2020, an intention client walked to our booth and asked us that one of their projects needs to be equipped with a high-pressure pump, and the requirement is that water can be pumped to a height of 800 meters. One of our sales representatives received her and said: the outlet pressure of our high pressure pump on axial piston principle technology can reach 80bar, which can meet your needs. Wonder why the sales rep used different terms?

Let’s see the origins of head, pressure

In Greece 2,200 years ago, Archimedes developed the first practical constant-flow pump. The "Archimedes screw" would elevate water from a river up into an irrigation canal for agriculture. The screw was used as a bilge pump on the king’s barge. It would also lift well water up to the surface for the wives to carry home and use to pour their husbands’ bath.

Beginning with the Archimedes screw and the Egyptian Noria (another pumping device), pump force was rated in units of energy against gravity. For this reason, pumps are rated in "head" to express what we call pressure.

In 1643 the French inventor and mathematician Blaise Pascal, realized that air (the atmosphere) also has weight and that its force is applied in all directions, not just down with gravity. So, he clarified the concept of "pressure" as it is used in the physical sciences: He defined pressure as a force applied to an area, such as a pound of force applied to a square inch of area: thus, pounds per square inch.

Buy and use efficient pumps

The pressure of the fixed displacement axial piston pump in high pressure applications mainly comes from external resistance, which is not very related to the speed and flow rate. The axial piston pump fixed displacement is related to the speed. For example, the calculation method of the theoretical flow value of BHP25 (unit: liters per minute) is as follows:

25ml/rev (geometric displacement) *1500 revolutions/1000=37.5 L/M. Because the axial piston pump in actual use of high pressure application scenario rotates once, there is leakage. After subtracting the leaked flow rate, it is the actual flow rate. Therefore, we divide the actual discharge flow rate of the hydraulic axial piston pump by the theoretically designed flow rate to calculate the volumetric efficiency of the pump, that is to say, dividing 35 L/M by 37.5 L/M, the volumetric efficiency of the BHP25 high pressure pump is about 93%.

The overall efficiency changes with the volumetric efficiency. The higher the volumetric efficiency is, the higher the overall efficiency. Generally speaking, the volumetric efficiency of AHP series axial piston pump and BHP series axial piston pump is about 92% (less than 93% because of high pressure), while the volumetric efficiency of DHP series axial piston pump is about 96%.

Flow and Speed Diagram

Flow and Speed Diagram

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