Siemens Control Valves and Valve Actuators
The control valve is where automation physically touches the mechanical system. A selection error here cannot be corrected by any controller, however good.
Control valve selection rests on three values: design flow, pressure drop across the valve and the resulting Kvs. Valve authority — the ratio of valve pressure drop to total circuit pressure drop — is typically targeted at 0.3–0.5. On the actuator side, required force, stroke and permissible close-off pressure must match the valve.
Kvs and valve authority
An oversized valve passes full flow in the first 10 % of its stroke and behaves effectively as on-off, causing the system to hunt. An undersized valve creates unnecessary pressure drop and raises pump energy.
Actuator matching
Actuator selection considers force (N), stroke (mm), running time, supply voltage and control signal together. Insufficient force means the valve does not fully close at high differential pressure, causing continuous leakage.
Values checked during selection
| Value | Why it matters | Typical target |
|---|---|---|
| Kvs | Passing design flow at the correct pressure drop | Nearest step below the calculated value |
| Valve authority | Control quality and hunting risk | 0.3 – 0.5 |
| Close-off pressure | Tight shut-off and leakage | Above system differential pressure |
| Stroke / force | Actuator fully driving the valve | Per valve datasheet |
| Control signal | Compatibility with the controller | On-off · 3-point · DC 0–10 V |
Product groups
- 2-way flanged control valves (VVF series)
- 3-way ball valves (VBI series)
- Threaded control valves
- Electromotoric linear actuators (SAV series)
- Rotary actuators (GLB series)
- Zone valves
Frequently asked
Are DN size and Kvs the same thing?
No. DN is the pipe connection size; Kvs is the valve's flow capacity. Valves with different Kvs values exist at the same DN, and selection is made on the calculated Kvs, not on pipe size.
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