Control with throttle

Control of the flow rate of a hydraulic system by flow resistances in general with the objective of controlling the velocity of a cylinder or motor. For this purpose flow valves, manually controlled directional valves, proportional or high response proportional valves are used (Figure D 46).

In a hydraulic system with constant pumps the flow rate not required Q V (Q V = Q 1 – Q N) is fed back to the tank (Figure D 47). The power converted into heat at the throttling point on the 3-way flow control valve is proportional to the product of Q v and the load pressure p L:

With all other methods (that is also with continuously adjustable valves) Q v must be reduced via the pressure-limiting valve, i.e. under full nominal pressure. In addition there is also the loss on relieving the useful flow Q N from the nominal pressure to the load pressure (Figure D 48):

If, despite these relatively high losses, control with throttle is used relatively frequently, this situation is because it is relatively cheap (constant pumps) and because it has a very high dynamic performance (up to a few hundred Hz for control with throttle using servo valves).

Alternative: Pump control

Figure D 46: Overview of control with throttle

Figure D 47: Energy balance for control with throttle a) 2-way flow control valve, b) 3-way flow control valve

Figure D 48: Q-p diagram with power loss on throttling using 2-way flow control valve