Precision Throttling and Tight Shutoff with Minimal Torque

The ring gear as an appropriate means of driving the movement of the petals to minimize torque

The globe valves used most often for process control typically require significant torque to operate, and the valve stem must complete at least one 360-degree rotation, to transition from fully closed to fully open. These torque and rotational requirements lead to larger, heavier actuators, which require more energy to operate.

Reducing the torque requirements of control valves is the most important area of improvement for reducing cost, emissions, and complexity. A reduction in torque requirements also increases the efficiency and reliability of control valves.

Although butterfly valves and ball valves often cycle from fully closed to fully open on a 90-degree quarter-turn, they still require significant operating torque, and produce fluid effects that make them less than ideal for process control applications.

How can valve OEMs deliver quarter-turn operation, with minimal torque, while still providing precision throttling and tight shutoff?

With the patented design of the Shutter Valve™, the engineering team at Clarke Valve™ has effectively addressed the challenge of reducing torque requirements and providing precision control and tight shutoff, through the use of a ring gear.

The ring gear in a Shutter Valve is a beveled gear, and it is mounted at a 90-degree angle to the pinion gear. The pinion gear transfers torque from the actuator and valve stem to the ring gear, using a quarter-turn motion to cycle from fully closed to a fully open port.

Ring gear animation in quarter turn control valve
Figure 1: The ring gear enables the Shutter Valve to deliver precise throttling and tight shutoff, with quarter-turn operation and low torque requirements. A pinion gear (top) transfers torque from the valve stem to the ring gear. The ring gear then drives the open/close motion of three interlocking petals of the Shutter Valve via three control arms.

Energy is then transferred from the ring gear to the three valve petals by control arms that link the ring gear to each petal. The ring gear is connected to each arm, and each arm is then connected to the other end of the petal. There are also three hinge pins mounted in the valve body, that act as a stationary connection point for each petal. Through this mechanism, the rotating motion of the ring gear is transformed into the pivoting movement of each petal, into (or away from) the center of the valve port. The ring gear essentially provides a torque multiplication effect, like a bicycle gear or the transmission in a car.

Figure 2: The components that work together to drive the movement of the three interlocking petals of the Shutter Valve: the pinion gear (left), the ring gear (left-center), one of the three stationary hinge pins (right-center), and one of the three pivoting control arms (right).

In addition to the leverage provided by this mechanism, the movement of the three valve petals also occurs in such a way as to further minimize torque requirements. In the Shutter Valve, the three petals open and close perpendicular to the flow of any process fluids being controlled, encountering minimal flow-related resistance. If you’ve ever seen a car become submerged under water, on television or in a movie, you’re familiar with this concept. The people trapped inside the car are unable to open the door of the car, against the force of the fluid pressure surrounding the vehicle. However, they can easily roll down the window, as the window is moving perpendicular to the force/pressure of the water.

As a result of this design feature, the Shutter Valve does not require the high amounts of torque needed by a butterfly or globe valve, each of which need to push against the force of the flow, for throttling or shutoff. In fact, no matter how much the pressure or flow rate are increased in a given process, the Shutter Valve does not require any additional torque to open and close. The same cannot be said for a butterfly or a globe valve, both which require more torque to operate, as the pressure increases in the pipe.

To further maximize efficiency and achieve reliable operation from the gearing in the Shutter Valve design, Clarke Valve has worked closely with our supplier Tracey Gear. Together, we have optimized the alignment and synchronization between the pinion gear and ring gear, by ensuring consistent tolerances between the gears. This degree of precision helps to prevent any backlash or play in the mechanism, delivering smooth and controlled operation. The reduction or elimination of play also minimizes energy loss and ensures the efficient conversion of torque into the opening and closing function of the valve.

By design, the ring gear is an efficient means of transmitting torque into the functional motion of the Shutter Valve. Only a quarter-turn of the valve stem is required for a dynamic range of process control, and the gearing of the valve ensures that minimal energy is lost.

These features allow customers who deploy the Shutter Valve to use much smaller, lighter, and more energy efficient actuators, thereby reducing the cost, complexity, and energy consumption, as described above, while increasing reliability and efficiency.