What is an ALLO® controller?

A control valve with independent drive!
Independent because it needs no additional energy from outside. It thus avoids the risks related to network-dependent supplies such as electricity, instrument or compressed air (network fluctuations, network interruptions, network outages).

External energy is not always available (use in the field, isolated intermediate stations, developing countries). This is where an ALLO®-controller often represents the only valve solution. Or maybe external energy has to be deliberately excluded for safety reasons. Then the independence of an ALLO®-controller is often a significant component in the safety philosophy of a plant.

Because an ALLO®-controller is naturally not a "perpetuum mobile", then actuating the valve uses only a small part of the energy which is anyway present in the medium. It can thus both keep downstream pressures constant (pressure reducer) and dissipate excess pressures (excess pressure reducer) - which may also be necessary in individual cases.

How does it work?
The pressure of the medium to be controlled is guided through a control element which moves the valve spindle by means of a lever, and thus opens or closes the valve. Because work is done against a weight, the working range and set pressure can be set exactly. This direct link between pressure and control results in such a rapid reaction that the ALLO®-controller can be protected against hunting by means of a damping cylinder.

It's all quite simple!
You can confidently let the ALLO®-specialists look after the intricacies of the ALLO®-controller. They determine the exact operational requirements, design the valve accordingly, optimise the functioning individually, know the appropriate material combinations, master the national and international regulations, and can adapt the valve to critical operating conditions and situations. ALLO®-Service, at the ready for commissioning and maintenance, is equally expert.

The ALLO®-controller is a complete control circuit in a compact unit. It is simple to flange in and adjust. Detailed instructions are supplied for this. Afterwards, it runs independently and reliably, often for many decades.

You should inform yourself about ALLO® M+R R+A Terschüren GmbH, now that you know what an ALLO®-controller is.

Originally, the ALLO®-controller was designed as a piston pressure controller. As a result of further technical development, the control piston component is today generally replaced by a metal bellows. Metal bellows control offers significant benefits in comparison with piston control:

• Low maintenance,
• absolute external leakproofness,
• insensitive to contaminations from the medium or exterior.

The operating conditions are what may limit the application possibilities of metal bellows controllers. Small (< 1 bar) and high (> 100 bar) pressures to be regulated, as well as temperatures over 450° C significantly restrict the use of metal bellows controllers. In this case, pistons with labyrinth seals are put to use.
Normally, metal bellows are also used as spindle seals. But here too, there are limitations due to high pressures and temperatures, and in such cases asbestos-free stuffing box packing is preferred.

Of course, all installed seals and packings are made from asbestos-free materials.

From the control technology viewpoint, the weighted self-acting ALLO®-controller behaves like an integral controller (I-controller). In comparison with the proportional controller (P-controller), which works against a spring force, the I-controller has the great advantage that it completely dissipates control deviations which occur, and it requires no lasting control deviation for its functioning. In the region of the set value, the adjustment speed is very largely proportional to the control deviation in size and direction, i.e. an I-behaviour exists.
When a control deviation occurs, the controller adjusts the throttle cross-section in the valve housing by means of a lever until the set value (e.g. the back pressure on the pressure reducer) is reached, and the control deviation is zero. The controller remains in this position until a new control deviation is measured by the control system. In contrast, the P-controller sets a throttle cross-section which deviates from the necessary cross-section by the proportional error. This results in an unnecessary consumption of energy or material in comparison with the I-controller.

The damping device of the ALLO®-controller, consisting of an oil-filled piston-cylinder unit, is a pure I-member. If the lever applies a force to the bored-through damping piston, then its speed of motion is directly proportional to this force. The flow cross-section in the damping piston can be adjusted, and so the adjustment speed can be influenced. A very sensitive adaptation to the controlled system is possible. For a stable controlled system, a rapid adjustment speed with a low damping effect would be chosen.
On the other hand, for a labile controlled system the adjustment speed would be reduced with a smaller flow cross-section in the damping piston.

The influence of the installed metal bellows with their typical spring rates results in a very small proportional error, and thus produces a theoretical Proportional-Integral behaviour (PI behaviour). This effect is however negligibly small, and so the ALLO®-controller may again be considered to be working integrally.