Overview of Pressure and Flow Selection of Hydraulic Pumps & Motors
Posted on 15/01/2024
1. Hydraulic pump pressure selection
Generally, medium and low pressure pumps below 80 kgf/cm2 are suitable for the following situations:
1. Occasions where the output of hydraulic cylinders and hydraulic motors is small and precise control of the correct position is required.
2. When the hydraulic cylinder is required to be sufficiently rigid.
3. Where the hydraulic pressure transmission distance is short.
4. When the power is small.
5. Due to cost requirements, cheaper pumps such as gear pumps or vane pumps need to be used.
High-pressure pumps above 200 kgf/cm2 are suitable for the following situations:
1. When hydraulic cylinders, hydraulic motors, etc. have large output and require high speed.
2. Where it is necessary to control the power loss between long pipes to a certain extent.
3. High power occasions.
4. Due to the use of high pressure, the size and weight of hydraulic cylinders, valves, piping, and mechanical devices are reduced, and the overall cost is reduced.
Under the condition that the hydraulic cylinder force and power are certain, increasing the pump pressure will correspondingly reduce the pump flow rate, thereby reducing the volume of the cylinder, valve, accumulator, fuel tank, pipe joints, and piping, and correspondingly reducing the weight. But when the pressure reaches a certain value and the reduction in volume and weight reaches the limit, if the hydraulic pump pressure continues to be increased, due to strength requirements, the wall thickness and other dimensions of each component need to be increased, causing the volume and weight to increase. The temperature rise of the hydraulic system is proportional to the pressure. The pressure is proportional to the deflection of the hydraulic cylinder. In addition, the size of the pump pressure also has a certain relationship with the reliability and life of the system.
2. Selection of hydraulic pump flow form
Dosing pumps are mainly used in systems with medium, low pressure and low power, or as auxiliary pumps in high-pressure systems. It is suitable for hydraulic devices with small changes in power and speed or short operating time. It has a large power loss and must be used in conjunction with a safety relief valve.
Variable pumps are mainly used in hydraulic systems of high-power and precision machinery or machine tools, especially hydraulic systems that have large changes in power and speed and work for a long time. It can improve system efficiency and reduce temperature rise.
Hydraulic systems often use high and low pressure combination pumps and fixed variable combination pumps to adapt to the power needs of various hydraulic devices.
4. Calculation of hydraulic pump motor power
The power of the motor driving the hydraulic pump can be calculated by the following formula
N=p·Q/612η (kilowatt)
In the formula: p - the hydraulic pressure at which the hydraulic pump consumes the maximum power (kgf/cm2)
Q——Flow rate when the hydraulic pump consumes maximum power (L/min)
η——Total efficiency of hydraulic pump
In the calculation of quantitative pumps, the rated pressure and flow rate are generally taken.
Variable pumps should be calculated based on the pressure-flow characteristic curve.
The pressure and flow rate of the double pump should be calculated according to the actual situation.
