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A review of the latest innovative designs for operating valves with a portable power tool.

 

Portable actuators are an increasingly viable system for turning valve wheels. Unlike fixed actuators they can be moved from valve to valve. This means just a single power tool (actuator) is required making the potential for big cost savings.

 

The reasons for adding any type of actuator to a valve are wide ranging, but commonly an actuator gives the ability to operate the valve either remotely or automatically when certain process conditions demand it. Also, valves above a certain size will require actuation simply because the effort required to turn the valve is greater than what can be applied manually. In these cases a reduction gearbox may be all that is required, however the gearing reduction may be so great that many hundreds of revolutions of the wheel are needed to fully operate the valve from opened to closed.

 

This is often overlooked at design stage; giving consideration to the likely duress on a person turning a valve wheel isn’t a design factor.

 

Then consider the issue of valves which have been in service many years. Neglect and failure to carry out the most basic maintenance will all lead to difficultly operating by manual means.

 

The portable actuator, also referred to as a ‘valve drill’ or ‘wheel turner’ or ‘windy gun’ has been around in various forms since the mid 1990’s. In the early days a pneumatic or electric torque multiplier device, more commonly used for bolt tensioning was used to operate valves. While this was functional, it was significantly over-engineered for this task (and very expensive). The torque accuracy associated with bolt tensioning, coupled with exceptionally slow spindle speeds meant this system was poorly suited to valve actuation.

 

In addition, the method of connecting the tool to the valve required a drive stem adaptor and some means of torque-reaction system. The wheel was discarded and a stem adaptor with an exact female facsimile of the valve stem fixed in place, along with a torque reaction bracket designed to clamp on the body of the valve. Again, this system was functional but supply was a lengthy process. Each valve requiring actuation needed to be surveyed to collect critical dimensions required for the design of the stem adaptor and reaction device.

 

Some manufacturers adopted a semi-universal system which clamped to the existing valve wheel. As above, these proved to be functional and remove much of the need for collecting valve dimensions. However this solution required a wheel drive plate for every valve. This inevitably can become costly.

 

In recent years, French manufacturer Modec have taken an analytical view of the key requirements for portable actuation and set about designing a new system, taking these key requirements into consideration. They concluded that a drive system that can be fitted to the valve wheel in a matter of a few seconds will provide optimum efficiency for operation. Thereafter, sufficient torque and speed delivery appropriate for the valve being operated are incorporated into the design.

 

When designing a universal system of wheel drivers, aspects of the valve wheel design variables come into play. There are two relevant features that make up a valve wheel design. The number of spokes and the rake, taper or dish of the wheel spokes.

Note: Wheels used on gearboxes fitted to large diameter ball valves have their spokes tapered away from the wheel hub to create clearance between the wheel rim and the valve body.

 

A wheel drive plate system must be able to accommodate the following features.

 

• Number of wheel spokes. The portable actuator drive plate will apply to torque to the edges of the wheel spokes. Commonly, valve wheels have 3, 4, 5 or 6 spokes joining the wheel hub to the rim.
• Tapering of the wheel spokes between wheel hub and wheel rim. A wheel with tapered spokes means that the head of the power tool must rest above the face of the wheel rim. The point of connection of the wheel drive plate is usually below the face of the rim of the wheel. Therefore the drive plate design must incorporate an extension tube to bridge this gap.

 

For valve wheels that are flat, i.e. have no taper on the spokes an innovative design is used which has spring loaded spoke ‘fingers’ which float in a ‘V’ shaped slot. The number of fingers matches the number of spokes. The fingers can move in the V slot such that when power is applied and the wheel begins the turn, the plate automatically adjusts to a concentric alignment with the wheel axis. This makes the task of the operator much less stressful.

 

 

For wheels with tapered spokes another highly innovative design is used. An inner and outer castellated plate system is used to grip the spokes of the wheel. The inner extension tube projects just above the wheel rim face making it easy to connect the power tool to the wheel drive plate.

 

And now consider the issue of torque reaction. Anyone who’s ever used a hand drill will recognise the feeling when the drill bit suddenly stops turning and the drill handle jars in the hand. Now consider a portable power tool which is turning at more than 10 times the amount of torque than a hand drill. The consequence of this torque jarring can be enough to knock the operator off his feet. Modec have adopted a very simple solution to mitigate this risk. A lanyard strap system is attached to the handle of the power tool at one end, and the other end to some fixed structure close by the valve. Attention is required to minimise the amount of torque transmitted through the lanyard by creating a right angle between the lanyard and the tool handle. Consideration must also be given prior to operation of the valve as to the direction of rotation. If the wheel is turning clockwise, the tool handle will try to turn anti-clockwise when load increases. The lanyard must be anchored accordingly.