There is a Pneumatic Flow Control Solution for Every Application
As many industrial applications rely on pneumatics to operate tools, machinery and processes, it’s important to understand how to precisely control pneumatic flow; however, the best way to achieve precise flow depends upon the application and its complexity. Finding the sweet spot of flow control in pneumatic systems is worth the effort as it will help maintain stable system air pressure, reduce leakage losses and keep tools and machines operating at peak efficiency, all of which will cut energy costs and improve the productivity of pneumatic applications.
The Benefits of Pneumatics
Pneumatic systems require little maintenance and provide a long service life. They are capable of withstanding the dust, shock, vibration and extreme temperatures found in industrial environments and they are generally safe to use in areas where there is risk of fire or explosions. However, in the past, pneumatic systems have been difficult to precisely control, limiting their application to simple on-off functions. But due to advances in pneumatic flow control technologies, that is changing and pneumatics are now being used around the plant in applications ranging from powering tools and processes to pneumatic circuits for motion control functions.
How is Pneumatic Flow Control Achieved?
Pneumatic flow is the speed and volume at which pressurized compressed air moves. Flow control relates to how fast the pressurized air is permitted to move within a given time period through a pneumatic system. Flow control is accomplished via flow control valves, which offer the ability to vary the flow (or speed) from one point to another within a pneumatic system. Some valves are used to regulate flow while allowing it to pass through another section, while other types are designed to allow the flow to pass, stop or change direction. The type of valve required will depend upon the goals and complexity of the application and whether the rate of flow needs to be regulated, accelerated, decreased, or changed.
Because there are so many different applications ranging from simple to complex, there are a variety of pneumatic flow control valves available:
- Traditional control valves are the most basic type, and limit control to fully open, fully closed or fully switched to a new flow path to control the stop, start and change in the direction of the flow of the air.
- Ball valves have a perforated, hollow, pivoting ball that adjusts the flow going through the valve. These are reliable and durable, but are strictly open or close valves.
- Butterfly valves feature a disk within the center of the valve and a rod connected to an actuator which passes through the disk. Due to the design, a pressure drop often results, and must be accounted for.
- Gate valves are linear motion valves and include a wedge-like disc that helps isolate the flow of air to provide a very tight seal, making them suitable for shutoff applications.
- Globe valves include a stationary ring seat along with a disk element. There are two halves to the body, separated by an internal baffle. Because they are always reverse seated, they are suitable for use in applications that require frequent operation and throttling, such as regulating the flow of air in a pipeline.
- Needle control valves are variable control valves and are not pressure compensated. The air will enter the valve and be forced to make two ninety degree turns. The design of the valve creates a pressure differential in between the upstream and downstream. It is possible to vary how much the needle restricts the path of flow, allowing users to change the flow rate by controlling the size of the orifice, permitting more or less air to pass as needed.
- Meter-out control valves are commonly used to control speed on pneumatic cylinders. They use a needle valve with a built-in check valve that allows free flow in the opposite direction of the regulated flow.
Pneumatic Flow Control in Complex or Unstable Conditions
While most of the flow control valves discussed above will provide basic and somewhat precise flow control, there are some applications that require more variable control or highly precise control and some instances where there are unstable conditions. In these cases, proportional control valves or electropneumatic control valves may be a better flow control solution.
- Proportional control valves regulate the flow of air through a larger pneumatic system. In proportional valves, the spool of the valve is driven with the help of a solenoid, which allows the valve to take any position between the input and output, thus adjusting flow between the two. To operate, solenoid force is balanced via a spring that positions the spool in proportion to the input, while a sensor on the spool detects when the spool has reached the desired position and cancels the solenoid signal, allowing the output pressure to equal the input pressure. This allows proportional valves to automatically change the output pressure or flow to match that of the input pressure, which either permits or prevents the flow of pressured air so that proportional valves can precisely regulate the rate, pressure and flow of air passing through a pneumatic system, making them suitable for use in variable pressure and flow applications that require fast response and consistent control. Proportional control valves provide the best flow control when there are pressure changes or flow variations in the system.
- Electropneumatic flow control valves provide an automated solution for adjusting flow. Electropneumatic flow valves combine flow control with an electrically controlled proportional solenoid valve and rely on a sensor and feedback loop to control flow. They may employ either a controller of their own or the control signal may be integrated into a PLC, allowing users to adjust flow electronically, in real time, based on feedback from the sensor. This type of control is best for applications that require extremely precise and very responsive control requirements such in motion control applications and small, but critical pneumatic circuits.
While pneumatic flow control is always a necessity, the most suitable solution will depend upon the application. Control valve technologies range from the most basic, manually controlled methods to more complex, automated solutions to suit every industrial need. But no matter what the application, choosing the most appropriate means of controlling pneumatic flow will provide benefits associated with controlling the amount of air and energy used and providing efficient operation of the equipment.
For assistance choosing the flow control solution that is best for your application, please contact a specialist at John Henry Foster.