What is in this picture? (Answer below)
Answer: Pneumatic valve exhaust muffler noise control measure.
What noise is it reducing?
In industry, many process machines have pneumatic valves that open and close things, start and stop things, move things. Compressed air is the force that does the job. Once the valve’s job is done, the compressed air is released as a very loud hiss. Think of air brakes on lorries that make a loud air release noise at traffic lights. This is the noise that these mufflers reduce.
Why should the noise be reduced?
Noise damages hearing. By law, noise emissions must be reduced if there is a risk to hearing.
How do mufflers work?
Pneumatic system exhaust mufflers/ silencers may be soft or rigid foam or may be packed with sintered material. The purpose of the muffler is to diffuse air coming out of a pneumatic system. Normally air released from a valve would be at high velocity and can create noise emissions in excess of 120 dB(A) with its interaction with background air. The muffler diffuses the released air, reducing its effect on the surrounding air and hence reducing noise emissions. Noise emissions from a muffled valve can be as low as 87 dB(A). Additionally, the muffler can filter out some of the oil and debris carried from the compressed air system before it is released into the workplace. This is necessary for the super “clean” environments of the food and electronics industries.
And why is the noise emission in the photo still high?
The mufflers pictured had holes made in them. The holes reduce the diffusive capability and negate the filtration capability. Dirty air is whistling out of the holes at 107 dB(A). It was photographed to prove a point so that action would be taken to reduce noise levels.
So why has it got holes bodged in it?
Oil and debris from the air system eventually clog up the foam (or other media). When the pneumatic valve releases the air, resistance to airflow enables a back pressure to be created, and this causes the valve to fail to open or close fully. Then the machine breaks down. Holes made in the muffler media allow the air to be released unhindered and the back pressure is prevented. (And the machine will carry on working.)
And the lesson is?
Mufflers on pneumatic valves are a hugely effective noise control measure that can reduce noise emissions by 20 dB(A), but they must be maintained and replaced regularly. Preventative maintenance is key to managing the control of noise from pneumatic valves.