Industrial Butterfly Valves

Resilient seated butterfly valve (Pratt)

Industrial process control valves are available in a very wide array of materials, types, and configurations. The first step of the selection procedure for a valve application should be choosing the valve type, thus narrowing the selection field to a more manageable level. Valve types, ball, butterfly, globe, and plug for example, are generally defined by the closing mechanism of the valve.

High performance butterfly valve (Pratt)

A butterfly valve uses a  flat disc that is positioned, paddle-like, in the fluid flow path. It rotates around a central axis (the stem) over a 90 degree rotational arc from open (position parallel to the flow direction) to closed (perpendicular to flow). Butterfly valves referred to as resilient seated are generally used in lower pressure, lower temperature applications and create a seal through compressing the disc into some type of elastomer seat. Another type of butterfly valve, used in higher pressure and higher temperature applications, are known as high performance butterfly valves (HPBF). They have highly machined discs and seats which are precisely seated together. Butterfly valve body materials include cast iron, bronze, and stainless steels. It is common to line the butterfly valve with another material to provide special protection from the process media.

Butterfly Valve Advantages:

• Lower cost
• Minimal lay length
• Easy to automate
• Generally lower torque

Butterfly Valve Disadvantages:

• High wear rate - seals are in flow paths
• Not a good choice as a control valve. Has a very nonlinear flow coefficient. 
• Not great for erosive flowing media.

Butterfly valves, like other valve types, have applications where they outperform. Careful consideration and consultation with a valve expert is a first step toward making a good selection.

Rotary Actuators in Fluid Power Systems

A rotary actuator is an output device for a fluid power system that delivers an oscillating motion over a limited range in less than one full revolution of the circle.

A true rotary actuator produces work by direct action of fluid pressure against internal vanes. Work is defined as a force applied over a distance. Rotary actuators produce a special type of rotational work called torque.

Torque occurs when a force acts on a radius. Since rotary actuators operate at low speed with high torque, torque output rather than the horsepower is used for the rating and identification purposes. Speed is a secondary consideration when choosing a rotary actuator for a particular application.

The typical units of measurement for torque are foot pounds (lb·ft). For example, if a rotary actuator with an arm length or radius of two feet were used to lift the two hundred-pound weight, then the resultant torque required to accomplish the work would be 400 lb·ft.

Understanding the relationship between the output torque required and the physical set up a fluid system enables designers to determine the appropriate rotary actuator for each unique application.

The video below illustrates the mechanics and the physics behind rotary actuators.

Pinch Control Valve for Wash Water Discharge in Treatment Plant

In wastewater treatment plants a pressure control valve is often needed on a standby pump to control discharge of wash water from the wash water pumping station.

Wash water discharge diagram using pinch control valve (Red Valve) 

Red Valve Series 5400

The main pump and the standby pump are rated to provide maximum flow at a constant pressure. A pressure sensor with integral transmitter is required to continually monitor system pressure. Under normal operating conditions, the pressure control valve is normally closed. After the surface wash shuts down, pressure from the discharge pump changes. The sensed line pressure is transmitted to a controller which sends a signal to the positioner on the control valve.

As the line pressure increases, a Red Valve Series 5400 control pinch valve opens. As the flow demand increases, line pressure decreases, and the valve closes. This system constantly maintains the pressure needed to operate the system. From the pressure control valve, the system discharges to atmospheric pressure over a clear well.

Due to the potentially high pressure drop conditions, the pressure control valve needs to be able to withstand the effects of possible cavitation. Red Valve Series 5400 control pinch valves, with their one-piece elastomer cone sleeve construction, are ideally suited for this application. The flow characteristics and pressure drop capabilities of the cone sleeve controls the flow and handles the pressure drop in the system. To assure cavitation does not occur, a TFO variable orifice to stage the system pressure drop by creating back pressure on the control valve. This setup fulfills the need of the treatment plant, and is a proven cost-effective, maintenance-free solution.

Reprinted with permission from Red Valve.