A proportional valve provides a change in output pressure or flow in the same ratio as the change in the input; for example, if the input doubles then the output will also double.
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Proportional Valves are suited to applications where output pressure will vary - either in steps or continuously. Stepped output pressure means the pressure is held at one value before the pressure is increased to another value. Continuous output pressure is where pressure is continually increased at a set rate.
Proportional Valves can be interconnected, for example, the output from one being used as an input to another. Many are programmable, with onboard diagnostics, making them highly suited to Industry 4.0 system design.
They are dependable, cost-effective (particularly air-pilot operated), give fast response and consistent control.".
Proportional Valves can help reduce cycle times, by quickly achieving a stable pressure. They have a fast, precise response, which will improve efficiency. They also give repeatable control and pressure output, giving an expected response each time.
There are some basic parameters to consider. Firstly, what is being controlled? Pressure, flow or some other characteristic. What input and output pressure range will be required, and at what range of flow rates? What is the likely operating temperature that the Proportional Valve will experience? Are there other environmental considerations, such as a wet and dirty application.
It is important to consider if the process is a static, a step-by-step, or dynamic one. This may very well dictate the response time required and hysteresis performance.
Cost may be a consideration and, as stated, air pilot operated valves are particularly cost-effective.
Proportional Valves are suited to analytical and test instrumentation, process applications such as tensioning, spraying and blow molding. They are also found in medical and foundry applications. However, they can also be used in many other applications. Please contact us with any specific enquiries.
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A throttle valve in the tank line of a conventional solenoid valve controls actuator speed in a meter-out configuration. The actuator cannot run away with a throttle valve at this location. Make sure the directional valve can withstand any backpressure in the tank line that is greater than the circuit produces.
One throttle valve in the main pump line can vary the speed to one actuator or several that cycle at different times. This type of circuit is less expensive but requires a more-complex electrical control circuit.
The throttle valve configuration in Figure 14-10 gives infinitely variable flow. Adding the hydro stat module to the pump line keeps the pressure drop across the orifices constant. With a constant pressure drop, flow does not fluctuate. Because the 4-way valve never sees reverse flow, both flow paths can supply the circuit. Either flow path has a nominal pressure drop at a specified flow. This arrangement gives twice rated flow without excess pressure drop or heat.
The parallel flow path module comes with all flow paths internally drilled and sized to keep pressure drop to a minimum. This module is available in D03 and D05 sizes for flows up to approximately 50 gpm.
Use proportional control valves to reduce shock and give a finer degree of control to circuits that do not require extreme position accuracy, or repeatable speed and force.
Proportional valves restrict flow to and from an actuator. They work best with a pressure-compensated pump in a closed-center circuit. An accumulator in the circuit enhances cycle response time and protects the pump from pressure spikes. Systems that use proportional valves usually require a heat exchanger because energy waste is higher with this type circuit.
The following sections describe a few more circuits ' with some pointers for using proportional valves in several applications. Always remember to size the valves for maximum flow and pressure drop to get optimum response and repeatability from the circuit.
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The circuits in Figures 14-11 and 14-12 control acceleration and deceleration of an actuator. Electronic signals to these circuits also can vary the speed of the actuators infinitely.
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