Redundant, self-monitored valves a safe and reliable choiceFebruary 23, 2017 REDWIRE is news you can use from leading suppliers. Powered by FRASERS.
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DM2 Series C and E valves from ROSS Controls are typically used as solenoid dump valves for air entry energy isolation. When a safety event occurs, such as the opening of a guard door or the operation of an E-stop device, these valves will exhaust the downstream pressure in the system, removing the pneumatic energy.
One question that is frequently asked when it comes to the integration of this valve in a safety system is why the valve doesn’t have two feedback switches for monitoring by the safety system. ROSS Controls addresses this important question in a white paper, entitled Pressure Switch Feedback in a Control Reliable System.
Why doesn’t the valve have two feedback switches for monitoring?
DM2 Series valves are redundant, self-monitored devices in which both independent elements must function within a specific timeframe of each other. This time will vary with valve size and supply pressure, but must remain below 150 milliseconds. If the valve operates abnormally due to an element not functioning synchronously with the other element within this timeframe, the valve will default to its exhaust condition. It will remain in that position until the main solenoids are de-energized and the independent reset solenoid is given a pulse signal.
These valves also have a pressure switch that functions as a status indicator, informing the machine controls that the valve is in an “operational” state or a “non-operational” state. The status indicator is not related to the inherent safety function of the valve, and is strictly a diagnostic device for use in an external device monitoring system. Because the valve has the redundancy, monitoring and cross-checking internal to it, and the status indicator pressure switch is not part of the safety function of the valve, there is no need for two valve position sensing switches.
Another question the company addresses in the white paper is how users should monitor the downstream pressure within the safety system. To get the answer to this question and more, read the white paper in its entirety.
To learn more about DM2 Series C and E valves, contact ROSS Controls.