In the case of the individual-valve solution, a multi-core cable is used to connect up the solenoid valve and sensor box. With the valve terminal the only reduction is the number of cores in the cable. The costs difference are negligibly small. The possibility of using two cables to control the individual valves has not been considered.
The calculation is based on the list prices of Festo products and standard products from other suppliers (solenoid, valves, tubing, cables, etc.). The costs include the components, the installation of lines and cables of appropriate length, and the connection costs. The installation and connection costs are those given by the end user.
The pneumatic lines are not considered. A careful local survey was conducted to determine the precise locations of the electrical cables and pneumatic lines for all the solenoid valves, which were then entered into a layout plan. This plan was then used to work out the cable and line lengths. A similar procedure was used for the upper floors.
Calculations were done for four variants, assuming the whole plant to be classified with respect to Atex as non-Ex (indoor), Ex zone 2 (indoor), Ex zone 2 (outdoor), Ex zone 1 (outdoor).
The results reveal a significant costs advantage in favour of the valve-terminal solution in all areas.
With regard to product and installation costs, the advantage is between 14 and 42 percent. An additional point for cost saving can be the pneumatic ring line (Fig. 3). The mathematical model can also be applied to installations of other sizes as a guide. This costs comparison covers only the investment costs. It makes no allowance for the further savings which can be achieved through the use of valve-terminal technology throughout the life cycle of production installations. For example, diagnostic techniques can be used to avoid downtime due to malfunctions, and any downtime which does occur can be significantly reduced through the rapid localization of fault locations.
Valve Terminals Will Be Speed Up Commissioning
Commissioning is often neglected during the planning phase. In the case of commissioning with individual valves, the system is fully wired and fitted with tubing. A compressed-air supply is then switched on and the solenoid valves are actuated via their manual overrides in order to check that the individual valves have been correctly connected.
In the installation shown, many process valves are hard to reach, frequently requiring a ladder. It is not possible to carry out on-the spot checking of allocation listings. The control cabinets are easily accessible for plant operating personnel. This means an enormous reduction in the amount of walking required during commissioning.
* The author is working as Industry Segment Manager Chemicals at Festo AG & Co. KG, Denkendorf/Germany.