The function realized by the constant power pump guarantees that the motor will not be overpowered at the time, the flow at low pressure will be high, and the flow at high pressure will be small; the constant pressure pump can realize zero flow and hold pressure.

 

1) The constant pressure pump is generally used in such a hydraulic system: the initial stage requires the low pressure to rapidly advance, and then it turns to the slow approach, and finally stops and maintains the pressure, like the hydraulic press. Here, the pressure set by the constant pressure pump is the pressure required by the system to maintain the 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 considered. In order to better understand the pump control system, it may be considered to modify the system pressure to be determined by the load and the constant pressure pump to the limit. In the case of presses, for example, the reaction force of a pressed part can be large, and how much is applied by a constant pressure pump.

 

2) The constant flow pump is mainly used for an engine on a construction machine. The power should be fully utilized. For the hydraulic system, high flow at low pressure and low flow at high pressure are possible. This is similar to a constant pressure pump on the surface, but it is not. The constant power pump follows 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 turning point to start the constant power. After entering the constant pressure working condition, in principle, the flow rate can be maintained according to the needs of the system while keeping the pressure constant.

 

3) The constant pressure variable pump starts the variable after reaching the set pressure of the pump's flat body. At this time, the flow rate drops down to a sharp line. The constant power variable pump is almost variable in the full pressure phase, basically ensuring that the output power is constant at a certain level. In the range, but within the power range set by the pump, the pressure rises and the flow rate is the full flow output. When this pressure is exceeded, the flow rate starts to drop to ensure that the output power is constant (this means that when the power is lower than the rated power, it is actually used. The power is not constant.) There is also an electronically controlled variable pump. Its 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 that it can save energy even if the pressure is not changed. Constant power pumps are capable of changing the speed of motion in response to changes in load, and are also used primarily in situations where such changes in load require speed to change.

 

5) 1) Under normal circumstances, there are few cases of using fixed power for fixed industrial hydraulics. Most of them are powered by the walking machine (engineering machinery). In order to make full use of power, there are many situations in which constant power pumps are used. Of course, the world is big and cannot be generalized.

 

6) For a system in which the parameters of pressure and flow have relatively large differences in the course of repeated cycles or during random operations, people often use the "one key to open a lock" mode to handle flexibly.

There are many options for the flow rate, such as: DC phase addition and subtraction (multiple fixed pumps in parallel), full AC (inverter motor driven quantitative pumps, variable displacement pumps), DC plus AC (several quantitative pumps , plus variable displacement pump), plus accumulator, etc., constant pressure constant power as mentioned before.

There are many ways to change the pressure, but in the end, it should be considered in conjunction with changes in the flow rate. For example, multi-stage pressure switching, electro-hydraulic proportional valves, proportional pressure pumps, boosters, and electric high-pressure pumps are used as booster pumps (both of which are local boosters), 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 the pressure and flow rate change, but the power is not.

 

8) There are two types of speed control: one is a pump-controlled motor system; the other is a valve-controlled motor system. The former scheme is:

1 quantitative pump + variable motor

2 Variable Pump (Inverter Motor + Dosing Pump) + Dosing Motor

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