This article discusses why a plant operator would revert back to the traditional ways of using Solenoid Valves in compressed air/gas applications in their plants.
Whilst this article identifies the benefits of the more common approach of using Ball Valves with Spring-return Pneumatic Actuators, the article highlights a particular Buschjost product which performs better than Ball Valves whilst adding more value. For a summary of this article and to see the benefits of the Buschjost range of 2-way Solenoid Valves at a glance please follow this link: Solenoid Valves Vs Ball Valves in Process Control applications.
The traditional use for solenoid valves up to 2” as isolation valves for process fluids where they have been seen as low-cost but quick-acting with fail closed or fail open operation, has to some extent gradually been replaced by ball valves with spring return pneumatic actuators. This is partly because of the demand by plant operators for feedback of the actual valve position, in this case by means of a switchbox mounted on the actuator. This is a widely used, readily available solution and as most plants have mains compressed air available, it is often seen as a preferred solution.
The increasing pressure on plant operators to cut running costs, reduce down time and monitor and reduce energy usage, is resulting in operators looking at ways of reducing losses in their steam and compressed air generation systems, both of which are very expensive to produce and maintain. There is also another increasing demand for isolated systems in remote plants where mains air is not available and electricity is the only motive power available. In this case electric actuators for ball valves do not offer failsafe operation without spending large amounts of money on battery back-ups or electro-hydraulic actuators and even then this solution cannot offer a comparable closing speed to a solenoid valve.
The current Buschjost range of 2 way solenoid valves includes options for position indication switches for applications up to 25Bar working pressure (16Bar 200 deg C on steam) with threaded connections up to 2” or flanged up to 4” DN100. The switch position is easily adjustable on the extended core tube which has a fluid tight seal separating the detection system from the valve internals. Atex approvals are also available on these units. These valves offer quick operation comparable or better than spring return pneumatic actuators with the position feedback capability inbuilt and a significantly lower lifetime running cost through lower energy usage.
The latest design from Norgren Buschjost uses what is effectively a second generation switch system. The original units were simple mechanical reed switches detecting the presence of a magnet within the solenoid core assembly but it was found that the performance and reliability could be significantly enhanced by moving to the current design using magnetic inductive switches. Using a 24vdc supply these offer PNP outputs and LED switch indication and there is an option for switches with II 1 GD Atex approvals.
We find that they are now a very attractive solution for design and project engineers looking to increase performance and lower energy demand in their systems. Typical installations where these valves are used successfully include fire suppression manifolds, chilled water distribution systems, isolation valves in diesel supply lines to generating sets and steam distribution systems where feedback and reliability are key requirements.
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