Valve Magazine - Spring 2011

cant reduction in turns while remaining below acceptable rim pull requirements. Optimizing for number of turns and/or rim pull can provide a manual operator solution for applications where traditional worm gears would exceed rim pull or number of turn limits.

The disadvantage of high-efficiency worm gears is cost. But while they are more expensive than a traditional gear operator, high-efficiency worm gears remain significantly less expensive than automating the valve.

High-efficiency gears also are especially well suited for applications where a portable driver may not be readily available, where utilities are not present for an actuator or where simplicity of design is a priority. These newer gears offer a simple solution for large, high-pressure valves that are infrequently operated, but where timely, safe operation is important—such as pipeline isolation or at pig launcher/receivers. High-efficiency gear units also carry a distinct advantage in subsea applications where the shortest time possible to cycle a valve is necessary to maximize productivity for divers or remotely operated vehicles.

As an alternative, manual gear units can be adapted to facilitate a connection between a powered driver and gear input shaft. While convenient and lower in cost than a fully automated solution, this driver system can include risks to personnel if executed improperly. If the adapter/con-nector is only a drive nut or other mating coupling attached to the handwheel or input shaft of the gear, unnecessary risk to personnel may result. This is because at initial startup, at the end of stroke, or if there is any stoppage of the valve mid-stroke, the torque no longer is imparted into the gear. Instead, it is imparted into the person holding the driver. A safer alternative is mounting the driver to the input shaft of the gear in combination with a torque arresting adapter (Figure 2). The adapter facilitates mounting the driver and eliminates the torque trans-

mitted to the user when the gear unit reaches the end of travel. Torque and speed limiters can be set to limit revolutions per minute and input torque to safe levels to avoid gear unit or drive train damage.

The driver system can be designed for portability to allow costs to be divided across a number of valves. The torque

driver system provides a cost-effective solution for cycling valves with high numbers of input turns within a reasonable period of time at minimal risk to or effort by personnel. When combined with a high-efficiency gear operator, this combination offers a cost-effective and efficient alternative to actuators for a

Figure 2. Gear with driver and torque arrestor

wide variety of large valves.

Increasingly, human capabilities (human factors) are defining the maximum sizes and/or pressure classes for valves that can be manually operated. Alternatives to traditional manual operations, such as portable operators or valve automation, carry their own set of personnel risks or costs. Recent offerings in the valve market including high-efficiency gears, and torque driver systems present solutions that are simple to plan, easy to implement, encourage safe operation of valves and avoid the high costs associated with actuation. As human factors become better defined and implemented by more users, designers might want to consider including these newer tools into their operator philosophies. VM

KEVIN SWICEGOOD is an engineering manager (contractor) at Cameron Valves & Measurement ( www.c-a-m.com) in Houston, TX. Reach him at kevin.swicegood@c-a-m.com.

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