Valves enhance machine and worker safety

To ensure a machine is properly safeguarded, it is important to evaluate the entire system, including the pneumatic valves operating within the system. This important topic was addressed in a recent white paper by ROSS Controls.

Provisions

According to the authors of the white paper, properly specified machine safeguarding systems must include provisions for pneumatic valves. These valves must be functionally redundant and monitored for faults. They must also return to a safe position in the event of a loss of pressure or other such event, and be able to inhibit further operation upon detection of a fault until it is corrected. There should be a dedicated, specific function reset input, and reset should not be automatic or triggered by removing or re-applying pneumatic or hydraulic power.

Valve safety

In addition to including provisions for pneumatic valves, the white paper says that it is important to understand the two abnormal conditions that affect valve safety. The first is similar to an electrical-control fault, such as when a relay might be stuck in the open or closed position. The second abnormal condition is when a valve develops diminished performance like, for example, if it becomes sticky or sluggish. In both of these cases, the valve reaches the proper position, but slower shifting affects safe stopping distances or precise timing. The ANSI B11.19- 2003 standard mandates a monitoring system that detects these conditions for critical applications, and the ANSI/ PMMI B155.1 standard requires diminished performance monitoring if stopping time can be affected.

A solution

An easy solution is to use a self-monitoring, Category-3 or -4 valve, designed to detect both conditions. Such double valves provide dual internal functions so that an abnormal function of one side of the valve does not interfere with the overall normal operation. At the same time, the double valves sense abnormal operation on either side of the valve, and then inhibit further operation until the problem has been corrected and the valve deliberately reset. Double valves are appropriate for pneumatic and hydraulic equipment when reliability is an issue.

A leading manufacturer

ROSS Controls is an international manufacturer of pneumatic valves, controls systems and safety products for the fluid power industry. The company's portfolio includes control reliable double valves.

To learn more, contact ROSS Controls.

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