Solenoid valves have come a long way since the first of the kind was invented by Automatic Switch Company (Asco) in 1910, says Alaa Industrial Equipment Factory (AFI), which markets the Asco range in the Kingdom.

''Thanks to development over the years, solenoid valves have witnessed many new applications, and more durable, reliable, compact and efficient products have been put on the market,'' says a spokesman for the Dammam-based AFI.

Elaborating on their functions, he says: ''Solenoid valves control flows by either blocking or passing the flow of a liquid or gas at a given pressure level. In large pipes with high-flow values, flow is generally controlled by butterfly or ball valves operated by pneumatic actuators. This drive mechanism is, in turn, controlled by a solenoid valve, now referred to as a pilot valve.

''Solenoid valves, particularly pilot valves, are today controlled by process control or PLC systems. The power consumption of solenoid valves should be as low as possible in order to optimise the cost-effectiveness and output-channel reliability of such systems. Less power means less heat in explosive situations, allowing a higher temperature classification. Back-up battery packs also last longer if the solenoids consume less power.

''As the functioning of the valve must never be impaired, the industry continuously demands more reliable solenoid valves to achieve longer MTBF (mean time before failure) intervals. The problem with several solenoid sizes is that the force needed to operate the valve will decrease significantly if the current is reduced.

''In DC environments in particular, the current drops when the temperature rises. When designing a solenoid valve, a minimum of 15 per cent extra should be reckoned with to compensate for fluctuations in power supply voltage and power losses caused by cable length.

''Manufacturers use several design and production techniques to achieve lower power consumption by pilot valves. Asco uses the following:

(a) reduction of friction and use of balanced valve construction.

(b) electronic circuitry to boost the electrical energy for operation

(c) more efficient solenoid design by using advanced 3D-CAD systems.

(d) use of new technologies to generate mechanical forces.

''The latest in sealing technology is used to minimise internal friction. Pressure balancing of the mechanical device reduces the energy required from the solenoid. These approaches do not impede the functioning of the valve but the effect on power consumption is limited.

''Most solenoid valves operate on 24V DC. On DC however, there is not the inrush current which is typical for AC-powered control and which adds extra energy to the operation. By using specific electronic circuits, an inrush current is generated artificially on DC. However, this increases the number of failure-prone components and causes a slight time lapse between actions as energy must be stored in the capacitors during each operation cycle.

''Market leaders employ sophisticated 3D CAD tools to arrive at optimum parameters for coil and magnetic circuits.

''One of the latest developments is pilot valves with piezo technology. A piezo element replaces the solenoid operator in the generation of mechanical movement. The use of a Philips ceramic multiplayer actuator (CMA) has resulted in pilot valves operating at a maximum of 0.3mA and with lifetime experiences. These valves are suitable for many applications including the control of larger valves, particularly so if combined with an intrinsically safe fieldbus.

''Many options are open to valve manufacturers to develop safe, reliable and efficient pilot valves with considerably lower power requirements. However, to prevent potential operational bottlenecks, users should carefully consider the operating conditions of the valves and the parameters required for optimum performance prior to acquiring valves incorporating the latest in low-power technology.''