Mechanical press safety standards and good practices require at least three functions should a valve fail that controls a pneumatic clutch or brake:
- Air must exhaust quickly to ensure fast stopping time.
- A monitor must take action to prevent further operation of the press.
- A method to alert personnel should be incorporated.
Double (dual) valves have all of these features, so they have become the press industry’s safety standard for clutch and brake control. These valves incorporate two valve elements that are independently controlled by two solenoid pilots within one valve body. The two valve elements share a common inlet, outlet, and exhaust ports. When the pilots are simultaneously energized, the elements operate to make the valve function as a 3-port, 2-position, normally closed valve.
Double valves, such as the DM2 Series D from Ross Controls, have built-in self monitoring and can send a signal back to press controls if a valve malfunctions. Each independent valve element monitors and cross-checks the operation of the other on each cycle. Therefore, if one side fails to operate properly, the valve immediately exhausts downstream volume to less than 1% of supply pressure. The built-in monitor places the internal elements into a locked-out condition to prevent further operation of the valve or the press. A momentary reset signal must clear the valve fault to continue operation. An optional status indicator switch can provide Go or Faulted signals.
Double valves provide a level of safety for clutch-brake circuits in mechanical presses that single element valves cannot — even when externally monitored. Therefore, double valves are known as control reliable, which means, “The capability of a device or system to stop or prevent initiation of hazardous motion in the event of a single component failure within the device or system.”
Control reliable devices can be applied anywhere potential exposure to catastrophic injury exists. Standardizing on double valves, such as the DM2 Series D, will simplify circuits and add a significant measure of safety.
Click here for more information on control reliability or to download a catalog on the DM2 Series D valve.