• Functionality and safety

Self-acting control valves  ─
The very crest in mechanical and plant engineering

The various elements in industrial plants are matched to each other as closely as possible in terms of layout and function. Valves are important components that perform necessary regulating or control tasks. They can be controlled hydraulically, pneumatically or electrically, or they can operate self-actingly.

Self-acting control valves are also referred to as self-operated regulators (German abbreviation RoH). They act independently, i.e. pressure control valves use the existing line pressure as operating energy and level control valves use the fluid level for this purpose. They neither require an external energy source nor an actuator to function properly.

Proven operating principle for modern plants.

Self-acting valves have been operating on exactly this functional principle for more than a hundred years. Upon delivery, plant operators receive a ready-to-connect and immediately functional valve whose long service life and reliability ensure safe operation even in demanding applications.
It is a fact that plants are designed and maintained to operate reliably in as many situations as possible. Nevertheless, natural events such as earthquakes or floods can throw a spanner in the carefully calculated works if the power fails. Then the plants quickly reach their limits.
But not self-acting valves! Saving resources, they function perfectly and control reliably even in these special situations.

Pressure reduction? Pressure reducing valves or back pressure regulators can do.

A pressure reducing valve reduces a high, often fluctuating upstream pressure (p1) to an adjustable, constant downstream pressure (p2). It is spring-operated, i.e. a spring keeps the valve open. The reduced downstream pressure is in balance with the spring force. If the downstream pressure is higher than the spring force, the spring, stem and cone move upward and the valve closes. The valve therefore protects equipment, valves and installations that are arranged downstream from excessive pressure. At the same time, it reduces consumption and minimizes flow velocity and noise.

Back pressure regulators limit or build up an adjustable, constant pressure upstream of the valve. They therefore control the valve upstream pressure (p1). They are also spring-controlled, i.e. a spring keeps the valve closed. The set upstream pressure is in balance with the spring force. If the upstream pressure is higher than the spring force, the spring, stem and cone move and open the valve. Back pressure regulators protect upstream equipment and installations from excessively high or low pressure, e.g. as a pump protection valve.

Layout of spring-controlled pressure control vavles

  1. Setpoint adjustment

  2. Setpoint spring

  3. Working diaphragm

  4. Controlled section

  5. Control element (throttle point)

Problems with air? Self-acting level control valves put things right.

All fluids contain air or gas in both start-up and continuous operation. There is a risk of pressure surges, bursting or implosion of the line caused by pump failures, emergency stops or system failures. However, gas bubbles also cause pressure losses at geodetic high points and thus contribute to energy waste.

Bleeding and venting valves are the solution here. They are installed at high points in the pipeline and automatically discharge air or gases or feed them in. They are float-controlled. Rising liquid level raises the float and closes the valve, usually via a lever system. When the liquid level drops, the valve opens and allows air to flow in.

Start-up bleeding and venting valves discharge air from plants with low internal pressure during start-up or filling. With their large seat diameter, they ensure rapid air discharge. During operation, they are kept closed by the internal tank pressure. In the event of a sudden vacuum, they open and ensure pressure balancing. This prevents damage caused by negative pressure.

Bleeding and venting valves for continuous operation are used to feed or discharge the air produced during plant operation. They have a lever transmission, so that they work even at very low and high pressures. If air supply is to be avoided during operation, the outlet is equipped with a check valve.
Combined bleeding and venting valves can be used for start-up as well as for continuous operation.

Steam traps, liquid and gas separators are also used for level control. In contrast to bleeding and venting valves, which are located at high points of the plants, the steam traps are arranged at the bottom of the pipelines. They self-actingly discharge the collected condensate without loss of steam or gas.
Liquid separators use the centrifugal principle. They self-actingly separate liquids and condensate from gas or steam flows and discharge them automatically. A rising level in the integrated separator opens the valve, while a falling level closes it.

Layout of float-controlled level control valves

  1. Float
  2. Lever
  3. Valve seat
  4. Shut-off body
  5. Liquid level

No deviations.

The proven functional principle of the self-acting control valves stands for the fast response behavior of this valve type, since the setpoint adjustment acts on the control surface immediately and without any loss. Detours via a control element are avoided.
The low installation and maintenance effort as well as the long service life of the valves with optimum selection also facilitate cost advantages in plant operation.

Build in and trust.

We said it before: Self-acting control valves work without external energy sources. A power failure has no consequences. Even in remote areas with inadequate infrastructure or in pipelines laid over long distances, self-acting valves perform their service reliably without any external control. Accidental maloperation is thus ruled out - set and forget!

Aspects for self-acting control valves that are convincing.


  • Proper functioning, even in the event of a power failure 
  • Proven functionality based on more than one hundred years of experience 
  • No risk regarding maloperation
  • Quick response behaviour of self-acting control valves 
  • Insusceptibility to computer viruses


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