Throttle valve with adjustable throttle (measuring throttle, A P), in which the flow remains constant through the combination of the valve with a control throttle (pressure compensator, A R), regardless of the changing load pressures p L. Here the control throttle releases a changing cross-section, which is inversely proportional to the load pressure. As a result, the flow p L remains constant, regardless of the pressure difference p P (Figure S 103).2-way flow control valve: The measuring throttle and the control throttle are connected in series so that there is only an inlet and an outlet (Figure S 104 a). The flow rate Q v that is not required must therefore be removed from the circuit via the pressure-limiting valve for the system; i.e. with high losses (cf. throttle valve).3-way flow control valve: The measuring throttle and the control throttle are connected in parallel. This creates a third connection on the control throttle, which is used to lead off the flow rate that is not required (b). This takes place under the respective load pressure plus approximately 5 bar; therefore, with less energy loss than with 2-way flow control valves (cf. throttle control). To configure the circuit of flow control valves, the flow control valves can be arranged between the directional valve and the working element. In this case, they operate only in the direction in which they are installed. They can also be arranged before the directional valve. Then they work in both directions (this arrangement is rarer). In addition, a distinction is made between an arrangement in the inlet, in the outlet and in the bypass (Figure S 105).2-way flow control valve in inlet (primary circuit, a): Fine-tuned control of the pump flow rate; pressure in the cylinder = operation pressure, pressure on the pump = nominal pressure of the system and therefore results in a higher power loss.
2-way flow control valve in outlet (secondary circuit, b): Required for pulling load. As the outlet is throttled, both sides of the cylinder are exposed to pressure; the lower volume on the rod side is controlled; the pump always operates against the nominal pressure, resulting in a high power loss.2-way flow control valve in bypass (bypass circuit, c): The controlled oil flow is fed into the tank and the residual flow into the cylinder. Fluctuations in the flow rate of the pump are passed on to the cylinder. Not suitable for accumulator operations. The pump only operates against the load pressure, resulting in as low a power loss as possible.3-way flow control valve (d): Can only be arranged in the inlet. The pump only works against load pressure, resulting in the lowest possible power loss.
Figure S 103: p-Q characteristics of throttle and flow control valves
Figure S 104: Schematic of a 2-way (a) and 3-way (b) flow control valve
Figure S 105: Circuit variants for flow valves 