The principle of the pneumatic cylinder is to use a vacuum in a compressed-gas system as the motive force for many devices.
The principal application is widespread and has seen continued development over several centuries, with new applications emerging constantly.
How does a pneumatic cylinder work?
A pneumatic cylinder is a cylinder that is compressed by air. The air may be stored in a compressed tank or provided by a compressor driven directly from an engine.
The piston P is connected to the function F through the cylinder in the figure. The piston moves in the cylinder under pressure from pressurized air from tanks T1, T2, and T3. When the pressure reaches the value of one atmosphere (i.e., 1401 kPa at 0C), the air inlet valve V3 is closed and equalizes with atmospheric pressure, and air flows into chamber C2 through pipe three until the pressure rises to 500 kPa (7 bar). A pressure regulating valve V3 is required on the pressurized airline.
The piston slides along its axis when the push rod P3 is pressed. The air inlet valve V2 is closed and equalizes with atmospheric pressure and air flows from tank T2 to chamber C1 through pipe 2 until it reaches a force of 500 kPa (7 bar). When the piston moves in direction Z, the volume of chamber C1 increases. The two valves (V1 and V2) regulating pressure in chambers C1 and C2 remain open until the pressure rises to 1,000 kPa (14 bar). At this stage, valves V3 and V4 are closed for them to be equalized with atmospheric pressure.
How are pneumatic cylinders powered?
- Compressed air tanks: As described above, three compressed air tanks power the pneumatic cylinders. Two or more valves separate these tanks to allow for three different pressures to be applied to the pneumatic cylinder.
- Compressor: A machine that uses some force (usually electric) to compress gas into a tank or another container. It would help if you had an empty tank at atmospheric pressure before using a compressor to fill it with gas.
- Air Flow Meter: A device used to measure the amount of air circulated by the compressor.
- Pressure Regulating Valve: This valve regulates the pressure applied to the pneumatic cylinder by connecting a drive or pumping system to a tank and a pneumatic cylinder.
- Air Inlet Valve: This device allows air into another chamber through an opening (like an airplane wing) and regulates how much air can be pumped in without creating excessive pressure and wear on equipment. As the speed of the pneumatic cylinder increases, so makes its demand for compressed air, and it will use more of it with more wear on getting more out of it from these open valves. This is why the air inlet valves must be adjusted to function correctly.
- Air Outlet Valve: This valve controls air flow out of the pneumatic cylinder when it is under pressure. The amount of force that can be applied to any object by a pneumatic cylinder will vary with how much air supply there is, which means that you may want to recalibrate it several times during a project to get desired results.
- Air Filtering System: This system allows contaminated compressed air into the tanks and filters out particles through static electricity or a chemical reaction.
- Air Pressure Gauge: This instrument is used to measure the pressure of compressed gas.
- Pressure Reducing Valve: This valve releases excess pressure into the atmosphere/environment with a small amount of gas as it allows compressed air to escape.
- Air Regulating Valve: This valve reduces airflow and controls airflow into a chamber through a pipe or tubing system.
What are the types of pneumatic cylinder?
Compressed air is not suitable for everyone’s needs; therefore, pneumatic cylinders were developed to accommodate diverse housing and fulfill various uses.
Airtight-controlled compartments have been developed in which a certain amount of pressure may be applied to the contents without being disclosed by an external opening other than a manually operated valve. These compartments are often used in conjunction with ventilation systems as they can contain an area that has no connection with the outside environment (air envelope) thereby creating an airtight environment large enough for working materials or personnel.
The pressure in storage compartments must be controlled by a pressure regulating valve, for example, an adjustable valve placed in the supply line. The output pressure must also be regulated to prevent excess pressure from entering the storage compartment. This can be done through an independent regulator with adjustment or by adjusting the pressure of the compressed air.
One of the main advantages of pneumatic cylinders is that they are easy to use and don’t create any hazardous levels of noise or heat. Compressed air is safe because it can be regulated and maintained under a set standard and is considered environmentally friendly since it contains no gases or liquids that could escape into the atmosphere. Also, compressed air can be recycled and reused, making it economically feasible.
Some of the drawbacks to pneumatic cylinders include:
Electronic pneumatic cylinders use small electric motors to produce a partial vacuum in a sealed chamber. Electronic controls turn the motor on and off. These systems are completely computerized in operation. Pressure may be maintained by suitable means such as a mechanically operated pressure regulator or an electric air compressor with a sensing valve. The system does not breathe or ventilate; it maintains pressure for the time that the motor is energized at predetermined levels.
This type of pneumatic cylinder is often used in robotics, both hobby level (inverse kinematics) and professional.
Pneumatic cylinders are frequently employed as actuators in industrial robots and smaller robots. The use of pneumatic cylinders as actuators in industrial robots is particularly advantageous because the same cylinder can be used for both open-loop control systems that measure force through a load cell and closed-loop control systems that measure the force with strain gauges. This allows an industrial robot to be effectively retrofitted with a modern closed-loop controller without changing its original open-loop manual control system.