Valve control heads eliminate need for the wasteful venting of air

In all process industries the objectives are to improve efficiency and maximise profitability, at the same time as ensuring repeatable product quality. Moreover, these all have to be achieved within the required environment of high hygiene standards, where reliable assurance of clean and cleanable pipework and equipment is paramount, such as in food and beverage plants.

In pursuit of these objectives, companies are prepared to invest heavily in new plant and equipment. However, in many cases, real savings and improvements in efficiency can be achieved relatively simply and at relatively low cost by focussing on cutting energy usage and reducing product wastage.

With valves, pumps and fans used widely in food and beverage production, the possibilities for energy savings are considerable. Take compressed air, for example; its generation is equivalent to about 10 per cent of industry's total electricity usage, rising to 30 per cent in some sectors. This highlights why companies have compelling reasons to pursue energy saving initiatives in this area, typically by avoiding leakage in their systems, and by employing more efficient compressor installations. However, one area that has been neglected, until now, is improved process valve control techniques, which can lead to reduced compressed air use through the adoption of on-actuator or in-actuator pneumatic solenoid valves.

At present, the majority of pneumatically piloted valves on production and process lines centralise pneumatic control around valve islands in a control cabinet or enclosure. This arrangement means that the pipework carrying the pilot pressure to the actual valve from the valve island can travel for many metres before it reaches the valve head. As a result, the venting cycle of the valves operation will exhaust proportionately more air than is necessary.

The solution to this problem is Burkert's type 1066 valve control heads. Developed for use in the food, beverage and pharmaceutical industries, these units provide a decentralised method of opening and closing of process valves automatically, eliminating the need for the wasteful venting of control air normally associated with pneumatic tubing between the process valve and its related control solenoid valve.

The control heads integrate electrical and pneumatic control components as well as position feedback units and, optionally, fieldbus interfaces for AS-Interface or DeviceNet. They are mounted directly above the valve body, and, because there is little or no distance between the actuator and the valve that it is piloting, there is no air bleed: it is sealed. With this system the pressure feed goes directly into the valve head and the control signal is supplied either from a local closed loop control sensor or switch; or from a PLC/machine controller via a control bus - AS-Interface or DeviceNet - or multipole (parallel) directly into the valve.

Similarly, adopting digital positioners with integral solenoid valve control heads for regulating modulating process control valves will automatically lead to air savings, as these will normally ensure zero-air use in their stable state. The traditional technique of process valve positioners incorporating pneumatic flapper-nozzle systems means that air is being bled constantly, even when the valve is at rest. This can average the equivalent of a 0.75kW (or one-horsepower) in compressed air for every twenty valves in operation; a large process site can therefore be using a vast amount of energy - unnecessarily.

Choosing the option of an embedded PID process controller, working in conjunction with the positioner, provides a fast-acting, decentralised control loop in combination with the associated process sensor. This arrangement also reduces complexity and saves unnecessary components and wiring.

Where the problem is wastage rather than energy reduction, this can be improved greatly by accurate monitoring of process fluids, using new, innovative techniques of pH and conductivity measurement, as provided by Burkert's new 8201 and 8221 units. With probes made to the highest standards of surface finish, and with the use of glass-free, food quality materials, the opportunity now exists for measuring and controlling process lines during production and cleaning.

- Burkert Fluid Control Systems is based in Brimscombe, Stroud, Gloucestershire, UK.


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