In pneumatic conveying, the conventional rule of thumb is that the line size should be no less than four times the diameter of the biggest particle. Also, be cautious how you estimate the dimensions. Make sure that you include enough space for error in measurement.
One way to measure a pneumatic conveyor is by using a tape measure to get an average line width over any given length. Divide the overall length of the conveyor by this number to get an approximate average hole size. Then choose a hole size large enough so that most particles will be able to pass through it.
Another way to measure a pneumatic conveyor is by using a sieve and food colorings to determine the minimum hole size needed to allow only single-colored pellets to pass through. Use colors that will not run or blend together during testing. For example, use red for some holes and white for others, then compare the results.
Yet another way to measure a pneumatic conveyor is by using a flow meter to find out the volume of air that passes through each hole per minute. This is useful to know when selecting the right number of blowers for your application. One thing to keep in mind is that more blowers means more power consumption.
The majority of pneumatic systems operate at pressures of 100 psi or less. Because of the lower pressure, cylinders and other actuators must be greater in size than their hydraulic equivalents in order to deliver the same force. As an example, consider a hydraulic cylinder with a 2 in. Diameter rod and a 4 in. Long stroke. The maximum load it can carry is (diameter) × (length) × (pressure in pounds per square inch). For our example this comes out to 0.56 lbf (or 566 N). A corresponding pneumatic cylinder would need to have a diameter of at least 1.4 in. For it to be able to lift the same load.
Because of the lower pressure, cylinders and other actuators must be greater in size than their hydraulic counterparts in order to deliver the same force.
However, some applications require higher operating pressures.
The majority of industrial pneumatic applications employ pressures ranging from 80 to 100 pounds per square inch (550 to 690 kPa). Hydraulic operations typically employ 1,000 to 5,000 psi (6.9 to 34.5 MPa), while specialized applications may require more than 10,000 psi (69 MPa).
Normal operating pressure must be high enough to provide sufficient force to perform work efficiently, but it should not be so high that it causes damage to equipment or leaks out of valves and hoses.
Pressure indicators are used to show when air tools and other equipment are working properly with respect to air supply. These indicators can be as simple as a water spigot attached to a hose leading to a float ball in the tool's tank. The ball will rise to the top of the tank if there is air in the line, thus indicating that the tool needs repair or replacement parts. More sophisticated indicators use electronic sensors to measure pressure directly at points where the indicator will be located (on tools or near their reservoirs). If these sensors detect low pressure they will activate an alarm or trigger repressurization of the system.
Air compressors produce air under pressure for use in pneumatic tools, nailers, sprayers, and other devices that require pressurized air. Air compressors come in two main types: centrifugal and axial-flow. Centrifugal compressors use a spinning metal disk called a impeller to create airflow.
Pneumatic air-consuming equipment, such as cylinders and rotary actuators, have a maximum operating pressure of 8 to 10 bar [115 to 145 psi]. However, actual experience has proven that 6 bar [90 psi] is the perfect pressure for pneumatic system operation. The reason is that at higher pressures there is a greater risk of leakage, which would cause unnecessary costs.
The operating pressure of the pneumatic system should be high enough to provide sufficient force to operate the equipment effectively, but not so high that it causes leakage issues.
For example, if you were to connect two cylinders together so they could work with one air source, the highest pressure available from your air compressor would be needed on both sides of the connection point to prevent leaks. If the connection point was made using metal, then it would need to be able to withstand a pressure of about 15 bar [215 psi] before leaking would occur. That's more than enough pressure to run most cylinders.
If you were to use rubber or plastic connectors instead, then only half of the required pressure would need to be available for them to hold air tight. With rubber connections, around 8 to 10 bar [115 to 145 psi] would be enough, while with plastic ones this would depend on how thick they are walled against gas leakage.