When it comes to selecting the right type of pneumatic directional Air Control Valve for any application, you have many options at your disposal. Each comes with its own specific function, so it is helpful to understand differences and pick the type best-suited for your requirements.
To help you arrive at the valve “type” that’s right for your pneumatic application, this post will highlight some basic requirements to consider.
Establishing the parameters
Actuators use an on-board system that measures the position of the valve with varying degrees of accuracy, depending on the application. A contactless, digital encoder can place the valve in any of a thousand positions, making it very accurate, while more rudimentary measurements can be applied to less sensitive designs.
One of the main areas of debate when specifying control valves is determining the size of the valve required. Quite often process engineers will know the pipe diameter that is used in an application and it is tempting to take that as the defining characteristic for the control valve. Of greater importance are the flow conditions within the system as these will dictate the size of the orifice within the control valve. The pressure either side of the valve and the expected flow rate are essential pieces of information when deciding on the valve design.
Inside the valve body, the actuator design is predominantly either a piston or a diaphragm design. The piston design typically offers a smaller, more compact valve that is also lighter and easier to handle than the diaphragm designs. Actuators are usually made from stainless steel or polyphenolsulpide (PPS), which is a chemically resistant plastic. The actuator is topped off by the control head or positioner.
Older, pneumatically operated positioners had a flapper/nozzle arrangement and operated on 3-15psi, so no matter what the state of the valve (open, closed or somewhere in between) the system was always expelling some compressed air to the atmosphere.
Compressed air is an expensive commodity, requiring considerable energy to generate and when a manufacturing line is equipped with multiple process control valves all venting to the atmosphere, this can equate to a considerable waste of energy. It is important, then, to establish not only the most appropriate valve design, but also a cost-effective solution that takes account of annual running costs.
Modern, digital, electro-pneumatic valves that use micro solenoid valves to control the air in and out of the actuator have introduced significant improvements for operators. This design means that while the valve is fully open, fully closed or in a steady state, it is not consuming any air. This, and many other engineering improvements, have made substantial advances in both economy and precision.
Valve seats can be interchangeable within a standard valve body, which allows the valve to fit existing pipework and the valve seat to be sized to the application more accurately. In some cases, this can be achieved after the valve has been installed, which would enable a process change to be accommodated without replacing the complete valve assembly.
Selecting the most appropriate seal materials is also an important step to ensure reliable operation. Steam processes would normally use metal-to-metal seals, whereas a process that included a sterilisation stage may require chemically resistant seals.
Having installed a new valve, setting it up is now comparatively easy and much less time-consuming. In-built calibration procedures, such as Bürkert’s X-tune, perform the initial setup procedures automatically, measuring the air required to open and close the valve, the resistance of the piston seals on the valve stem and the response time of the valve itself. Once complete, the valve is ready for normal operation.
In the case where one control valve cannot provide the necessary rangeability, consideration of the use of two or more valves becomes necessary.
One solution is to use clean, instrument air to replenish the spring chamber, preventing any contamination from entering. This offers a defence against the ingress of airborne contaminants by diverting a small amount of clean control air into the control head, maintaining a slight positive pressure, thus achieving a simple, innovative solution. This prevents corrosion of the internal elements and can make a significant improvement to reliability and longevity in certain operating conditions.
In addition to the above-discussed tips, you can discuss your requirements with the manufacturer. Whenever you are considering these valves for your project, ensure that they are sourced from a reliable supplier like Ningbo Lida Pneumatic Complete Sets Co., Ltd, you can click https://www.nblida.com/ to learn more information