We run across a lot of applications in our industry, and one of our customers had a very specific need. They asked, “How can I automatically control the pressure in my air receiver?”
This is not an unusual dilemma and is normally solved by some type of proportional valve. The customer needed very quick dynamic control of the pressure in his receiver. More importantly, he wanted to control flow rates exceeding 50 SCFM which can be challenging given the other requirements. This customer also ideally wanted to use the same proportional control valve for the different flow rates. In addition, the solution had to be robust, easy to implement, and cost-effective.
Although this wish list seems difficult to accommodate, we were able to find a solution that met all of his requirements.
Proportional Control Valves
The key to this solution is the use of proportional control technology. Proportional control technology is ideal where precise performance is required in variable pressure and flow applications. In addition to this application, the combination of electronics and mechanics in proportional valves provides ideal performance for many other industrial applications.
Proportional valves — which change outputs in proportion to their input value — provide dependable, cost-effective, compact solutions for fast response and consistent control at relatively low flow rates.
For this particular application, a direct-acting proportional control valve was chosen due to its pressure control resolution, short overshoot settling time, and ability to quickly control the pressure with an analog input. In direct-acting proportional control valves, a direct-acting proportional coil solenoid is used, which acts directly on a piston or spool to adjust valve open or closed positions, based on varying voltage across the coil. This product is ideal for this type of dynamic pressure control application.
However, these devices, especially direct acting proportional control valves, are typically used for relatively low flow rates. This particular customer needed this dynamic control but with varying flow rates exceeding the capabilities of these valves (about 46 SCFM). Fortunately, we were able to accomplish this using the direct acting proportional valve to control a pilot operated regulator. Using this solution, we could use one type of proportional valve for a variety of flow rates while keeping the cost down.
Options are available for proportional valves with high flow rates, but they tend to be much more expensive. This solution sacrifices some resolution, but for the customer’s application, this was not an issue. This series of pilot operated regulators have nominal flow rates from 60 SCFM to 325 SCFM and port sizes from ¼” NPT to 1” NPT.
Using this solution, we were able to control the pressure with an analog signal using the Sentronic D proportional valve. This solution is very robust because the Sentronic D has a simple construction with minimal moving parts. This solution is also very easy to implement using the Data Acquisition Software (DaS) for the Sentronic D valve.
By connecting the SentronicD to a PC with an RS232 interface, the DaS can be used to optimally adjust the valve’s control parameters to a specific application. This solution is also very cost effective as the Sentronic D valve is reasonably priced and includes the free DaS tuning software. In addition, we are able to use the same Sentronic D proportional valve with different pilot operated regulators for different flow requirements, especially the high flow applications required. Due to our technical expertise and extensive product lines, we were able to provide this solution to meet all of the customer’s requirements.
For more information on this proportional technology: Numatics Proportional Technology catalog and Numatics Proportaional Valve Selection Made Simple.