Figure 1: Pneumatic silencer examples
A pneumatic silencer is used to vent pressurized air to the atmosphere. They are commonly installed on pneumatic 5/2-way solenoid valves, pneumatic cylinders, or fittings. Depending on the flow and pressure of the air coming out of the exhaust port, the pneumatic air exiting the device could produce noise that is potentially harmful to workers in the surrounding environment or cause noise issues in the application (theatre applications). In addition to noise, the exhaust air may emit contaminants during operation. Using a silencer exhaust cleaner can prevent harmful contaminants from entering the environment. Standards defined by organizations such as OSHA (Occupational Health and Environmental Control Agency) are enforced by governments to help protect workers from harmful noise and contaminant exposure. Figure 1 shows examples of common pneumatic silencers.
Pneumatic air silencers, also commonly called pneumatic mufflers, are a cost-effective and simple solution to reduce noise level and unwanted discharge of contaminants from pneumatics. Silencers can also include adjustable throttle valves to control the flow rate of air as it exits the silencer. Flow rate control with a silencer throttle valve can be useful to control the speed of a driving device and works similar to a needle valve. For example, pneumatic cylinders are commonly equipped with a throttle valve to control the piston actuation and/or retraction speed.
A Pneumatic silencer’s function is to vent pressurized air after it has performed work at a safe noise level and to prevent contaminants from exiting (if it is combined with a filter). Excessive noise may be produced as the pressurized air is released to the environment. Noise is the result of turbulent air which is produced when the fast-moving air released from the vent collides with the static air of the environment. Typically, silencers are installed directly at the exhaust port of a valve and diffuse the released air through a larger surface area which reduces turbulence and thus decreases noise levels. Pneumatic exhaust silencers are commonly designed with a porous material to increase the surface area of the exhaust port which it covers. They can also be installed on hoses.
Pneumatic silencers are designed in differing shapes depending on the application. Application specifications that influence design are housing materials, working temperature ranges, working pressure range, and connection options. Additionally, silencers can be specified with a filter to prevent contaminants (i.e. oil) from being discharged into the atmosphere (see section silencer exhaust cleaner). The two most common design styles are cone (Figure 2 left) and flat shaped silencers (Figure 2 right).
Figure 2: Cone silencer (left) and flat silencer (right)
Silencer housing material should be selected according to application. Housing material will influence the silencer strength, environment compatibility, pressure range, and temperature range. The housing material should be considered carefully during selection. The most common housing materials are sintered brass, sintered plastic, and stainless steel.
Sintered brass is a lower cost option for a durable metal housing. An example of a sintered brass silencer is shown in Figure 3. This material is suitable for non-corrosive and neutral environments.
Figure 3: Sintered brass silencer
Sintered plastic is low cost, light weight and offers high chemical resistance with higher noise reduction compared to metal materials. An example of a sintered plastic silencer is shown in Figure 4. This material is suitable for corrosive environments.
Figure 4: Sintered plastic silencer
Stainless steel is an excellent choice for applications which require corrosion protection, durability, and/or operating in a sterile environment. An example of a stainless steel silencer is shown in Figure 5. Stainless steel is commonly used in food or pharmaceutical applications. Stainless steel is generally more expensive than bronze or plastic silencers.
Figure 5: Stainless steel silencer
Silencers are suitable for high or low temperature applications. Material should be specified appropriately, especially in extreme temperatures. During selection, ensure the silencer material can operate correctly across the entire operating temperature range of the application.
Pneumatic silencers are specified with an operating pressure. The silencer should be selected in accordance with the correct operating pressure to ensure optimal noise reduction and reduce premature failure. The surface area of the silencer is dependent on housing material and shape. Surface area will impact the overall size, mechanical strength, and noise reduction of the silencer. Additionally, the resulting back pressure during operation will prevent proper machine operation if not selected correctly.
Pneumatic silencers are connected to ports using a threaded male end. The port could be on a pneumatic solenoid valve (5/2-way for example), pneumatic cylinder, etc. Common thread standards used are NPT (National American Pipe Thread), BSP (British Standard Pipe), or metric (ISO standards). Using a push-in silencer allows it to be easily moved from one device, or hose, to another.
The pneumatic silencer symbol seen in schematics is shown in Figure 6.
Figure 6: Pneumatic silencer symbol
Figure 7: Throttle valve examples
Throttle valves are commonly included with silencers and are commonly just called adjustable pneumatic silencers or flow control silencers. Adjustable pneumatic silencers are an inexpensive method for pneumatic flow control to control the speed at which air exits the valve. For example, by controlling the exhaust speed of a pneumatic cylinder you can control how quickly the piston is able to extend and/or retract. The flow rate of air is typically adjusted by rotating a knob to change the flow speed, like a needle valve. The position of the screw will increase or decrease the size of the valve orifice and thus adjust the flowrate of the air exiting the valve. Figure 7 shows an example of a throttle valve.
The pneumatic throttle valve symbol seen in schematics is shown in Figure 8.
Figure 8: Pneumatic throttle valve symbol
Silencers can also contain a filter to remove oil mist and dust in the exhaust air from entering the environment. These are important if the pneumatic air is dirty or toxic to allow you to protect the environment, workers, and/or applications if working in a sterile environment. Figure 9 shows an example of a silencer exhaust cleaner.
Figure 9: Silencer exhaust cleaner
The silencer exhaust cleaner symbol seen in schematics is shown in Figure 10.
Figure 10: Silencer exhaust cleaner symbol
To protect workers from exposure to harmful noise and toxic substances levels, organizations and governments define standards for machine manufacturers. Pneumatic silencers are commonly certified to the following standards:
Pneumatic silencers can be applied in many applications. Applications which operate pneumatics at a high frequency and produce a large amount of noise are well suited for pneumatic silencers. The application examples below commonly use pneumatic silencers.
Robotics: Robotics frequently use pneumatics to control movement or perform work on a load. A robotic arm for example, uses pneumatics to control its motion. Switching on or off pneumatic valves will control movement of the arm. Robotics are commonly used in conjunction with workers, so controlling the exhaust noise is important.
Packaging: Pneumatics are often used on packaging machines to drive motion. A sorting machine will often divert product based on a signal from an industrial controller. The signal from the controller is used to activate a pneumatic device. Due to the high rate at which packaging machines operate and the high volume of workers that are typically surrounding these machines, pneumatic silencer would be well suited for packaging machines.
Fence Production Machinery: Machines that produce rolls of fence often include pneumatic cylinders to cut fencing as it is woven into rolls. An operator is constantly working alongside fence production machinery to ensure the rolls of fence are according to specification. To protect operators from damaging noise a pneumatic silencer is an ideal solution to reduce noise from the constantly operated machinery.
Below is a list of frequently asked pneumatic silencer questions:
A pneumatic silencer and pneumatic muffler refer to the same device. The term silencer is commonly used in British English, whereas the term muffler is commonly used in America.
It is recommended to routinely clean silencer threads and the housing exterior depending on usage. Dirt and dust can build inside the threads or housing of silencers, especially in polluted exhaust environments. This prevents damage from blockages and reduces the possibility of downtime.
Depending on the frequency and pressure requirements of your application. A sealant can be applied to the thread of the silencer to ensure it remains tight during operation.
Silencers should be mounted such that contaminants do not block the silencer or exhaust port. For example, a horizontally mounted silencer will allow contaminants to drain through the silencer using gravity. This prevents damage from blockages.
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