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About Constant Power Variable Pump and Constant Pressure Variable Pump

2018-04-27

The function of constant power pump is to ensure that the motor will not overpower, large flow at low pressure and small flow at high pressure. Constant pressure pump can realize zero flow and pressure maintenance.
The function of constant power pump is to ensure that the motor will not overpower, large flow at low pressure and small flow at high pressure. Constant pressure pump can realize zero flow and pressure maintenance.
 
1) Constant pressure pumps are generally used in such hydraulic systems: at the beginning, low pressure is required to advance quickly, then it is turned to approach slowly, and finally it stops and keeps pressure, as is the case with 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 hydraulic system pressure is determined by the load, and the relief valve is limited" should be met. In order to better understand the pump control system, it can be considered to be modified to "the system pressure is determined by the load and limited by the constant pressure pump". Like the example of the press, the counter force of the pressed part can be very large, and the specific amount is adjusted by the constant pressure pump.
 
2) The constant flow pump is mainly used for an engine on such equipment as construction machinery, and its power should be fully utilized. The hydraulic system can be large flow at low pressure and small flow at high pressure. This is similar to a constant pressure pump on the surface, but it is not. The constant power pump follows the constant power when the pressure and flow change, while the constant pressure pump is the quantitative pump with the maximum displacement before reaching the set value, and there is no inflection point to start the constant power. After entering the constant pressure condition, in principle, the flow can be provided according to the needs of the system while keeping the pressure unchanged.
 
3) The constant pressure variable pump starts to change after reaching the set pressure of the pump flat body. At this time, the flow rate drops to a steep line. Constant power variable pump is almost full pressure stage in the variable, the basic guarantee that the output power is constant within a certain range, but within the power range set by the pump, the pressure rises and the flow rate is full flow output. When the pressure is exceeded, the flow rate begins to drop to ensure constant output power (that is to say, when the power is lower than the rated power, the actual 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 of the motor and the oil pump must be considered.
 
4) The more important point of the constant pressure pump is to save energy under the condition of constant pressure. Constant power pump can change the speed of movement according to the change of load, and it is also mainly used when the speed can be changed due to the change of load.
 
5)1) Under normal circumstances, there are few cases in which fixed industrial hydraulic pressure uses constant power. Most of them are mobile machinery (construction machinery) powered by engines. In order to make full use of power, there are many cases in which constant power pumps are used. Of course, the world is big, can not be generalized.
 
6) For a system with relatively large differences in pressure and flow parameters during repeated cycles or random operations, people often use the "one key to open a lock" model to deal with it flexibly.
There are many options for large and small flow rates, such as: DC phase addition and subtraction (multiple quantitative pumps are connected in parallel), full AC (variable frequency motor drives quantitative pumps, variable displacement pumps), DC plus AC (several quantitative pumps, plus variable displacement pumps), accumulator, etc. The situation of constant pressure and constant power is as mentioned above.
For pressure changes, there are many ways, but in the end, it should be considered in combination with flow changes. For example, multi-stage pressure switching, electro-hydraulic proportional valve, proportional pressure pump, booster, plus electric high-pressure pump as booster pump (both of which are local booster), and so on.
 
7) Constant pressure is used in working conditions where the pressure does not change, but the flow changes; constant power is used in working conditions where the pressure and flow change, but the power is not limited.
 
8) There are two schemes for speed regulation: one is a pump-controlled motor system; One is a valve-controlled motor system. The former scheme is:
1 Quantitative Pump Variable Motor
2 variable pump (variable frequency motor quantitative pump) quantitative motor