What are the differences between a self-operated valve and one with an actuator?

A self-operated valve uses the energy of the fluid itself (gas or liquid) to regulate itself; it does not need an external power supply or signal. An actuated valve (e.g., pneumatic ) is moved by an external device governed by a control signal (on/off or modulating), ideal when dynamic precision and integration with PLC/SCADA are required.

A self-operated valve (also called self-regulating) is a device that maintains a stable process variable —usually the downstream pressure (P2) —by leveraging the balance of forces between the fluid pressure and an elastic element (spring/diagram) or a piston/bellows.
It requires no electricity, instrument air, or positioner: the process itself is its energy source and signal.

Table of contents

1. In normal service, the shutter remains in the position that sustains the setpoint value.
2. If P2 rises, the spring–diaphragm/piston assembly corrects the opening to absorb the variation and return to the set-point.
3. Upon regaining equilibrium, the valve stabilizes the line again without external intervention.

1. Autonomy and simplicity: fewer components, fewer points of failure.
2. Reliability and low maintenance: ideal for environments with few control signals.
3. Proportional response: stabilizes pressure variations without “saw teeth.”

Some of our most requested valves:

• Pressure reduction/stabilization in industrial water, compressed air, neutral gases, or steam.
• Processes with fixed set-point and stable demand.
• Installations where robustness, contained cost, and ease of assembly are prioritized.

• M1, M2 (robust regulation in service networks, also steam).
• PRV20, PRV30, PRV44 (compact; balanced by piston or bellows; very versatile in laboratory, gases, and high temperatures).
• VD (direct action with piston for water and neutral gases).

Related articles:

An actuated valve incorporates an external mechanism —pneumatic, electric, or hydraulic—that positions the shutter based on a control signal (e.g., 4–20 mA). It allows working on/off or in continuous modulation within a PID loop, with setpoint changes in real time and integration in PLC/SCADA.

1. High precision and repeatability in flow/pressure/temperature.
2. Fast response and dynamic control in the face of disturbances.
3. Easy automation (interlocks, sequences, remote control, records).

1. Processes with variability of flow or pressure and changing setpoints.
2. Need for traceability and advanced control from the plant system.
3. Functional safety requirements (failure positions, interlocks).

C1 (pneumatic actuator): control valve for modulating or on/off service, with 4–20 mA positioner option, top-entry design for agile maintenance, and versions/materials compatible with industrial regulations and demanding environments. Ideal when the process demands precision, stability and automation without sacrificing mechanical robustness.

• Stand-alone reduction and stabilization of pressure in industrial water, compressed air, neutral gases, or steam.
• Networks with few control signals, fixed setpoints, and need for robustness and low maintenance.
• Plants where simplicity, rapid installation, and contained TCO are prioritized.

• Processes with variable set-points, PID loops, sequences, and startups/shutdowns with ramps.
• DCS/PLC integration with remote control, safety limits, and interlocks.
• Lines that require fine precision of flow/pressure/temperature and traceability.

1. Fluid and conditions (P/T, corrosivity, cleanliness). Defines body, trim, and elastomers (stainless steel, PTFE, EPDM, FKM) and the appropriate family.
2. Control requirement. Is proportional pressure modulation sufficient (self-operated), or is modulating control with changing setpoints required (C1)? Consider precision, dead band, and hysteresis.
3. Process dynamics. Response times, possibility of cavitation/noise , and presence of water hammer; dimension by Kv/Cv and not by DN.
4. Available energy and signals. Are there instrument air and 4–20 mA /digital I/O signals? If not, favor self-operated valves.
5. Regulations. PED/CE and, if applicable, ATEX (zones 1/2/21/22) with its thermal class and marking on the plate.
6. CAPEX/OPEX and maintenance. Consider initial cost vs. savings due to efficiency/automation and ease of maintenance (e.g., top-entry in C1).

• Using self-operated valves where fine modulation is needed.
  Avoid: define the control strategy before choosing; if there are variable setpoints, choose C1.
• Dimensioning by line DN instead of by Kv/Cv.
  Avoid: calculate flow rate, ∆P, P1/P2 and select by Kv/Cv with a reasonable margin.
• Ignoring compatibility of materials and packings.
  Avoid: compare chemistry and temperature of the fluid with available steels/elastomers.
• Forgetting ATEX requirements or actuator temperature.
• Avoid: verify ATEX zone and T class, as well as thermal limits of the actuator/positioner.

If you want to get the valve selection right the first time, we are by your side from start to finish. The Valfonta technical team can dimension Kv/Cv, validate materials and elastomers according to the fluid and temperature, verify regulatory compliance (PED/CE and ATEX when applicable), and recommend the optimal model among our self-operated valves (M1, M2, PRV20, PRV30, PRV44, VD) or the C1 pneumatic actuated valve for on/off or modulating service.

What we can prepare for you:

• Review of process data: flow rate, P1/P2, ΔP, temperature, density/viscosity, state (liquid, gas, steam).
• Calculation and selection: nominal size, Kv/Cv, closing class, trim, and connections (threaded or flanged DIN/ANSI).
• Materials: body and internals (stainless steel, carbon steel, bronze), gaskets and membranes (PTFE, EPDM, FKM, etc.).
• Application engineering: modulating control (PID loop), failure positions, noise/cavitation requirements, and water hammer.
• Technical documentation: product data sheet, installation and maintenance manual, CE/PED marking, and ATEX declaration if applicable.
• Maintenance plan and spare parts kits to maximize availability and reduce OPEX.

To expedite the study, please provide us with: fluid, maximum and minimum flow rate, pressures (inlet/outlet), temperature, line and connections, environmental conditions (including ATEX zone and thermal class if applicable) and any space or integration limitations with PLC/DCS.