Trying to hold pressure or flow in a process line with a manually-adjusted valve is an expensive habit in the age of automation. Proportional valves change their opening in proportion to an input signal, making that adjustment continuous and automatic.
Basic Signal Range
4-20 mA or 0-10V | Signal size → spool position → flow
1. How Proportional Valves Differ From On/Off Valves
A classic solenoid valve only knows two states: fully open or fully closed. A proportional valve, given an analog signal, gradually changes coil current - and therefore spool position - according to the signal's magnitude.
1.1. How the Analog Signal Becomes Motion
The solenoid inside the valve produces a magnetic force proportional to the incoming current; that force pushes the spool a certain distance, and that distance determines flow. When the PLC signal changes, the valve settles into its new position within a few hundred milliseconds.
| Characteristic Type | Low-Opening Behavior | High-Opening Behavior | Typical Use |
|---|
| Linear | Proportional, predictable | Proportional, predictable | Constant pressure drop |
| Equal Percentage | Precise, fine control | Stable, wide range | Variable pressure drop |
| Quick Opening | Rapid flow increase | Limited extra control | Mostly on/off use |
2. Advantages in Process Automation
- Precise Flow Control: can hold flow within 1-2% precision, decisive in color-critical processes like painting
- PID Integration: working with pressure/flow feedback, corrects setpoint deviation within seconds
- Remote Adjustability: setpoint can be changed via SCADA/PLC without operator intervention
"A proportional valve removes the wait for 'the operator to notice and intervene' that manual valves require; the system corrects itself within seconds."
— BRS PROSES Engineering Team
3. Field Challenges
Proportional valves can stick when fed with dirty or humid air, causing delayed signal response - installation without an FRL unit isn't recommended. If the PLC's analog output card resolution is low (below 12 bit), the precision the valve offers can't be used in practice.
4. BRS Proses Proportional Valve Integration
We determine the right valve and sensor combination together based on your existing PLC infrastructure:
- PLC/SCADA compatible valve and sensor selection
- Full installation with FRL unit
- PID loop tuning and field commissioning
- Characteristic curve recommendation based on your process data
