How to Select a Liquid Proportional Valve
Proper selection of the liquid proportional valve depends on matching of valve features to real working conditions of the liquid system.
1. Determine the liquid medium
Find out if the valve is going to handle water, oil, coolant, chemical solution or any other liquid. Find out the liquid viscosity, concentration, temperature & chemical compatibility. Body and seal materials must be compatible with the selected liquid medium.
2. Define the required flow range
Identify the minimum, average and maximum flow rates required. Select the valve with sufficient capacity, but which would still provide useful control resolution at low flow range.
3. Check the operating pressure
Identify the inlet pressure, outlet pressure, differential pressure and possible pressure spikes. The valve must have rated pressure and differential pressure ranges large enough for the whole system.
4. Choose the control signal
The common industrial control signals are voltage signals and current signals. Ensure that the valve input is the same as the PLC, controller, driver or automation system.
5. Consider the response time
Fast response valves are suitable for dynamic applications requiring fast flow adjustment. If the process is slow, then slow response might be acceptable.
6. Evaluate the accuracy and repeatability
If the application includes dosing, laboratory equipment, process control or precise manufacturing equipment, you should consider stability of proportionality characteristics, repeatability, low hysteresis and suitable feedback options.
7. Check temperature requirements
Temperature of the liquid and the temperature of the surroundings. Body materials, seals and electrical components must be suitable for the conditions.
8. Check the connection and installation requirements
Check the port size, connection type, mounting dimensions, valve orientation, space available for installation and electrical connector requirements.
9. Control method selection
Determine whether open loop control is sufficient or closed loop operation with pressure, flow or position feedback is needed.
10. Service requirements review
Consider operating cycles, accessibility for maintenance, spare parts availability and cleanliness standards.
Give all the information about operating parameters of the valve to the manufacturer for OEM applications so that the proportional valve can be properly sized and configured.
How to Prevent Typical Mistakes in Liquid Proportional Valve Design
Don’t choose based on port size alone. More important are the flow coefficient, the pressure differential and the actual flow range.
Don’t forget liquid compatibility. Check the valve body, seals, coatings and internal materials for liquid compatibility.
Don’t oversize the valve. Oversized valve will give poor low-end flow resolution.
Don’t undersize. Undersized valve will cause excessive pressure losses and will affect system performance.
Define the control signal in the beginning. Confirm voltage, current, PWM or any other control requirements before finalizing the actuator.
Consider minimum controllable flow. The maximum flow doesn’t define the quality of proportional control.
Consider pressure fluctuations. Pressure fluctuations will affect the relationship between the input signal and the flow.
Consider temperature effects. Temperature will affect the viscosity of the liquid and performance of the seals.
Allow filtration. Small internal passages and regulating elements can be clogged.
Calibration schedule. Specify the relationship between the control input and the flow at the time of commissioning.
Fail-safe mode. Determine the behavior of the valve in case of loss of power or control signal.
Service design. Allow easy access for inspection, cleaning, replacement and troubleshooting.
Test the entire system. Valve performance should be checked using the actual pump, piping, liquid, pressure and controller.
