Mechanical Key Interlocking Is Simple Way of Protecting Valves

Credit: Smith Flow Control has added a dust plug with mechanical key interlocking to its line of valve protection equipment.

Smith Flow Control has added a dust plug with mechanical key interlocking to its line of valve protection equipment.

Many times, simple trumps sophisticated when it comes to mechanical devices. Case in point: Smith Flow Control's latest iteration of its dust plug, which is designed to protect valves and aid operations in extreme environmental conditions.

The company has also added a durable, drawstring-tightened cover made of polyester fabric to provide an extra layer of protection.

Developed primarily for valves used in harsh environments such as deserts, which can see multiple sandstorms daily, and offshore oil and gas rigs buffeted by salt spray, the plug and cover are touted as effective and simple solutions to help users protect equipment in extreme operating conditions.

Smith Flow Control, which specializes in mechanical valve control equipment and is based in Witham, England, announced the product additions early in July.

"Today, our interlocks and coded keys are built very similarly to when we first introduced these products in 1985," said Clive Lyme, customer services manager. "However, the environments in which our products are being placed are continuing to diversify, and changes since then have reinforced the reliability of our products and their suitability for a broad range of applications."

The range of applications can even include clean production environments such as those for pharmaceutical chemicals, owing to the effectiveness and security of the locking mechanism on the plug. "We have gained market leadership and share by keeping [our equipment designs simple and robust," Lyme said. "The same principle applies to our dust plugs and dust covers - they are simple solutions."

The dust plug, which has a body of durable and chemical-resistant high-density polyethylene, covers the interlock-key entry point where coded keys are inserted to lock and unlock a valve. For an additional degree of protection, it also has a self-sealing interior weather strip that seals the key aperture in the interlock once a key is removed.

The dust plug is made of robust plastic and entirely mechanical in its operation. Credit: Smith Flow Control

The dust plug is made of robust plastic and entirely mechanical in its operation. Credit: Smith Flow Control

Dust plugs can remain in the interlock-key entry points until an operator is required to work a valve. Smith Flow Control designed the interlocks with color-coded lock-unlock tags with alphanumeric access codes specific to each production site. On top of the interlock body are tamperproof screws, designed to prevent tampering and ensure that the interlocks perform reliably.

Here is how it works: The interlocks are designed to release and trap operating keys in accordance with a user's operating specification. An initiating key, usually stored in a control room, is inserted in the free or open key-entry point. As the initiating key passes a code-activated section within the interlock body, it actuates a gear peg that rotates, enabling operation of the valve.

Operating the unlocked equipment immediately traps the key. When this operation is complete, a secondary key is released, thereby locking the equipment in a new position.

The activation procedure is "not high-tech, but effective," Lyme said. "It is not over-engineered - it works even if there is a power failure on site because it uses a mechanical design. Mechanical key interlocking provides a simple, fail-safe way of protecting plant assets and keeping workers safe, even in hazardous and stressful conditions."

Meanwhile, the dust cover provides an additional level of protection in harsh environmental conditions. The cover is fabricated with UV-resistant additives to prevent degradation from outdoor exposure, and it is designed to fully envelope an interlock unit. The cover protects both hand-wheel and lever-operated assemblies, and the drawstring allows operators to tighten the shroud and keep it firmly attached to a valve.

"The bag is made from a heavy-duty polyester fabric, which is incredibly durable, even under the constant impact of sand, wind, and water," Lyme said. "It is suitable for the most extreme temperatures, both hot and cold, and offers an extra level of protection."

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