The function of constant power pump is to ensure that the motor does not overpower, large flow at low pressure and small flow at high pressure; Constant pressure pump can achieve zero flow pressure.
1) Constant pressure pumps are generally used in such hydraulic systems: the beginning stage requires low pressure to move quickly, and then turn to slow approach, and finally stop moving and maintain pressure, such as hydraulic presses. Here, the pressure set by the constant pressure pump is the pressure required for the system to maintain pressure. Here, the basic principle of "the pressure of the hydraulic system is determined by the load, and the relief valve is added to the limit" should be in line. In order to better understand the pump control system, you can consider modifying it to "the system pressure is determined by the load, and is limited by the constant pressure pump." Like the example of the press, the reaction force of the press can be very large, and the specific amount applied is adjusted by the constant pressure pump.
2) Constant current pump is mainly used in construction machinery on this equipment on an engine, to make full use of its power. The hydraulic system can have large flow at low pressure and small flow at high pressure. This is similar to the constant pressure pump on the surface, but it is not. The constant power pump follows the constant power when the pressure flow changes, and the constant pressure pump is the maximum displacement quantitative pump before reaching the set value, and there is no inflection point at which the constant power begins. After entering the constant pressure condition, in principle, the flow can be provided according to the needs of the system and the pressure remains unchanged.
3) The constant pressure variable pump starts after reaching the set pressure of the pump flat body, and the flow rate drops into a steep line. Constant power variable pump is almost the full pressure stage in the variable, basically to ensure that the output power is constant within a certain range, but in the power range set by the pump, the pressure rises, the flow is the full flow output, when exceeding this pressure, the flow begins to decline to ensure that the output power is constant (that is to say, when below the rated power, the actual use of power is not constant). There is also an electronically controlled variable pump, whose variable curve is determined by the electronic control part and has nothing to do with the actual pressure. In any case, the power matching between the motor and the oil pump must be considered.
4) The more important point of constant pressure pump is that it saves energy when the pressure is unchanged. Constant power pump is able to change the speed of movement according to the load change, but also mainly used for this load change requires the speed to change.
5)1) Under normal circumstances, fixed industrial hydraulic selection of constant power cases are less, most of the walking machinery (construction machinery) power is the engine, in order to make full use of power, the selection of constant power pump is more. Of course, the world is too big to be generalized.
6) For a system in which the two parameters of pressure and flow have relatively large differences in the process of repeated cycles or random operations, people often adopt the mode of "a key to open a lock" to deal with it flexibly.
There are many options for flow, such as: DC phase addition and subtraction (multiple quantitative pumps in parallel), full AC (variable frequency motor drive quantitative pump, variable displacement pump), DC plus AC (several quantitative pumps, plus variable displacement pump), plus accumulator, etc., constant pressure constant power situation as previously said.
For pressure changes, there are many ways, but finally it should be combined with flow changes. For example, multistage pressure switching, electro-hydraulic proportional valves, proportional pressure pumps, plus superchargers, plus electric high pressure pumps as booster pumps (both are local booster), and so on.
7) Constant pressure is used in conditions where the pressure does not change, but the flow rate changes; Constant power is used in conditions where pressure and flow vary, but the power is not on either side.
