12 tips for selecting and sizing pneumatic and hydraulic components
July 11, 2013
In today’s typical manufacturing facility, hydraulic and pneumatic systems serve as the primary means of power for most cylinders, tooling and even some drive systems. They can be operated in high-temperature as well as high-radiation industrial environments where most electronic instruments will not function properly.
Volumes of material exist on proper system design, proper sizing of components, circuit design, valve and control technologies, as well as other design considerations. However, here are a few tips you may not find in the textbooks:
1. Flow vs. pressure. When dealing with pneumatics it is critical to understand the difference between pressure and flow. Too often operators compensate for starved flow with increased pressure. It is often best to install over-sized supply lines to a process in order to ensure the appropriate volume of air.
2. Use electric actuators. With ever-increasing energy costs, designers should consider using energy-efficient electric movement, provided the application requirements fall within an electric actuator's performance capabilities. This technology has advanced rapidly over the last five to 10 years, with vast improvements in functionality, including more precise movement and even built-in sophisticated controls.
3. Valve sizing. Correct sizing of components, including piping, valves and actuators, can improve the productive capacity of pneumatic systems. Valve sizing is particularly important. If the flow capacity is too small, it can have a negative impact on production cycles. If you want to improve production cycle time and quality, then proper sizing is critical.
4. Align pipelines. If pipelines are not aligned properly at the correct angle, as indicated in the installation drawings, there is a great possibility of equipment damage.
5. Choose 3-position valves. Wherever operators will be working near an operation, a 3-position valve is a better choice than a 2-position valve. This is because a 3-position valve will stop the equipment instantly in the event of an emergency. This is in contrast to a 2-position valve, which will first complete the operation before stopping.
6. Check temperatures. Be sure to check the surface temperatures of equipment during preventive maintenance time and make a record. High temperatures could damage the viscosity properties of the hydraulic oil.
7. Built-in flow control. When you are using a pneumatic cylinder in a project, especially In high cycle count projects, use a fitting that has a flow control valve built in to make the cylinder last longer.
8. Use feedback sensors. Don't rely on software interlocks to control pneumatic devices unless you account for the delay caused by physical actuation. 100msec is a long time in the computer world. Always back up actuators with electrical feedback sensors, redundant if possible.
9. Parallel air. Make sure you have an adequate air supply when using pneumatic technology. Costly leaks are often hard to detect in a noisy plant environment. To avoid failure in the supply of compressed air on a network, it is important to verify that the distribution is closed so that the compressed air comes in parallel and not in series. Inspect tubing, ferrule, connection and joints for leakages. Make sure the air being produced is dry. All air filters should be checked periodically for accumulated water drainage.
10. Choose quality tubing. To prevent leaks, use nylon tubing on machines rather than push-on fittings and PE tubing. The leakage often found with soft tubing is hard to detect in a plant environment.
11. Inlet side flow control. In a pneumatic logic circuit controlling a double-acting cylinder, place the flow controls on the inlet side of your cylinder depending on the direction of travel. Air is compressible and positioning will float if controlled on the outlet. This will also create back pressure.
12. Low fire risk. One of the advantages of pneumatic technology is that it can operate without using electricity. This minimizes the risk of fire or explosions from sparks or arc flash events. This technology is particularly useful in a plant making edible oils or hydrogenating oils or when using flammable gases in the production process.
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