Simplicity holds the key to design and component selection

Neil Saunders, general manager at Bürkert Fluid Control Systems, looks at pneumatic process control systems and the common components and processes involved - from the most basic design to a complete production line

A wide variety of industries have adopted the use of pneumatic process control systems, and as the complexity of these control systems grows, so it becomes even more important to ensure high levels of reliability and integrity. However, not every system requires a huge valve island or bus communication to achieve the required level of automation.

Pneumatic control has been in use for many years, especially in the pharmaceutical and food and beverage industries where hygienic conditions must be maintained to a very high standard. Pneumatics have many advantages, including a simplicity of design, low maintenance requirements and reliability, due in part to the use of compressed air as the power source, which is effectively inert and readily available. In addition, these systems are intrinsically safe and so can also be used in hazardous atmospheres, such as those in the petro-chemical industries.

Centralised and decentralised

Modern control systems can be divided into two groups - centralised and decentralised. As the names suggest the main control functions will either be grouped at a central point or located at the point of control, such as a process control valve. A centralised control solution is the more traditional solution and will usually involve a control panel containing a bank of control solenoids which are connected to the process control valves using air lines alone.

In a decentralised system, the air supply is fed direct to the control valve and the integral control head uses control signals to determine what action is required. The choice of system is dependent on the application since both have their advantages depending on the circumstances. The crucial point is to ensure that the system is properly designed and installed to ensure efficient and reliable operation.

Once the design scope is agreed, even for the simplest of installations, it is important to ensure the proposed design will produce an effective and efficient control system which will be easy to maintain and, if necessary, clean to the required standard. Although many of the components used in a pneumatic control system are relatively cheap, the cost of generating the compressed air is not and so it is crucial that the air is used in the most efficient way.

Air preparation

The first step is to clean and regulate the compressed air supply to the control system using air preparation units which filter and regulate the air supply. These units remove water and oil aerosols while also controlling the system air pressure, all of which makes them crucial to ensuring correct operation of the system as well as reducing wear and corrosion of the components.

Air preparation units, such as the type TPM001 from Bürkert, are available with a range of filter sizes, down to 0.01µm, as well as having the option of an activated carbon filter which can remove oil aerosols to a level of less than 0.005mg/m3. In addition, a range of connection sizes is available as well as ATEX certification to comply with regulations when operating in hazardous atmospheres.

As the system starts to take shape, so there is a need for flow restrictors, one-way valves and check valves to ensure that the air pressure and flow direction is correct for the equipment it is supplying.  These need to be matched to the application with regard to construction material, sealing properties and connection sizes, to ensure reliable and efficient service. An example is Bürkert’s TRG001, which contains a complete range of restrictor valves, check valves and flow control valves, with non-standard versions, materials and seals also available.

All of this equipment will need to be connected together and this requires careful selection of connectors - threaded, push-in or a combination of both. In all cases the application is the deciding factor when determining the correct design of connector, especially the material choice, which could require FDA approval or the corrosion resistance of stainless steel. Whether installing a new system or making alterations to an existing one, access to a wide range of reliable connectors with the necessary approvals is crucial.

Bürkert has developed a range of individual products for use in pneumatic process control systems as well as a process for designing, building, installing and commissioning complete systems - from the simplest closed loop control system, to the largest factory wide production facility with the latest fieldbus communications and intelligent control valves.

Customers first discuss their requirements with technical sales staff and then each project is assigned a team of experts, including designers, construction and installation engineers as well as a project manager who oversees the entire process from concept to delivery.

Bürkert Fluid Control Systems

www.burkert.co.uk

T: 01285 648 720

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