Exercises: Pneumatic circuits

Explain what pneumatics is and name two everyday devices or machines that operate on compressed air, stating what motion each one performs.

Name the basic components of a simple pneumatic circuit and explain in one sentence the function of each one.

In the diagram in the figure, there is a component marked with ?. State what component it is, what function it performs, and describe what happens to the cylinder rod when it is actuated and when it is released.

Name three machines or services in your environment that use compressed air (dentist's office, gas station, road construction...) and explain what job pneumatics performs in each one.

Explain what a compressor is and why every pneumatic circuit needs a compressed air source (compressor or cylinder) to operate.

Explain what the piston rod of a pneumatic cylinder is and what type of motion it performs. Draw or describe a cylinder, pointing out the barrel, piston, rod, and spring (if it has one).

You can do it on paper and send a photo with your answer.

Explain what an air exhaust is in a pneumatic valve and explain why an air leak causes less contamination to the environment than an oil leak in a hydraulic circuit.

Differentiate between pneumatics and hydraulics: state which fluid each one uses and one characteristic advantage of each technology.

Explain the difference between a single-acting cylinder and a double-acting cylinder, and describe what is observed when releasing the push button in each case.

Put the path of the air in this circuit in order: cylinder, compressor, control valve. Then, explain why the valve is placed between the air source and the cylinder and not after it.

A bus door opens and closes using a pneumatic cylinder that must push in both directions. Explain what type of cylinder and what type of valve it needs, and why a single-acting cylinder with spring return controlled by a 3/2 valve would not be suitable.

A service unit (filter, pressure regulator, and lubricator) is usually placed before the circuit. Explain what each of its three parts does and what happens to the valves if the air arrives dirty or with uncontrolled pressure.

A double-acting cylinder is controlled by a 5/2 valve. Explain in your own words what these two numbers mean (five ports, two positions) and how the valve enables the rod to extend and retract.

A flow control valve is installed in a cylinder line. Explain the purpose of regulating the air flow rate and how it affects the movement of the piston rod; give an example where a slow movement is desirable.

A circuit with a single-acting cylinder does not retract when the push button is released, and the spring is in perfect condition. Reason what other component might be failing (think about where the air leaves the chamber) and how to check it.

Describe, ordering it by stages, the complete working cycle of a pneumatic drilling machine that advances quickly, drills slowly, and retracts quickly: which valves and adjustments would make each stage possible.

In a workshop, the rod of a single-acting cylinder extends normally when pressed, but returns very slowly when released. Analyse at least three possible causes (leaks, worn spring, dirty valve...) and explain how you would check each one.

To actuate a stamping press using a pneumatic cylinder, an elementary circuit is proposed with a manual push button that switches a monostable valve: pressing it lowers the press and releasing it raises it by means of a spring.

1. a) Justify why this design fails to comply with basic industrial machinery safety regulations and which pneumatic logic element (two-pressure valve or "AND" valve) must mandatorily be incorporated to implement a two-hand control for operator protection.
2. b) Design the improved circuit by describing precisely which components you would use and how you would connect the pressure lines between the push buttons, the logic valve, and the actuator.
3. c) Predict what would happen if the operator attempts to bypass the system by permanently jamming one of the two push buttons with a clamp, and reason what additional synchronism condition modern industrial safety requires.

A technical office must choose the drive system (electric or pneumatic) for two different industrial applications in a factory:

1. A positioning robotic arm for assembling microcomponents, which requires an accuracy of 0.1 mm and holding intermediate positions fixed with rigidity.

2. A pusher for a packaging area in a flour mill, where the environment contains suspended combustible dust and packages may frequently jam against the mechanical stop.

For each of the two applications, determine which of the two technologies you should choose and justify your decision by analyzing: positioning accuracy, behavior under mechanical overload stall, and ignition risk in explosive atmospheres.

Describe in words a circuit design in which two cylinders move simultaneously actuated by a single push button. Analyse what synchronization problem might arise if one carries more load than the other and how it could be mitigated.

An operator looks at the pneumatic circuit shown in the figure and claims that, in the resting position depicted, the cylinder rod will remain at an intermediate point because compressed air enters simultaneously through both chambers and the pressures balance out.

1. a) Reasonably refute the student's claim: identify the valve marked with ? (number of ports, number of positions, and type of actuation/return) and deduce in which exact position the rod will be before pressing the push button.
2. b) Describe the complete operating sequence: explain what occurs in each chamber of the cylinder while the push button is held down and what happens exactly at the instant the push button is released.
3. c) If the driven load extends with excessive acceleration and slams into the end-of-stroke stop, indicate which auxiliary component you should install, in which specific line you would place it, and in which direction to regulate only the advance speed without slowing down the retraction.

In a pneumatic heat-sealing machine, the rod of a double-acting cylinder must extend downwards upon briefly pressing a push button, maintain pressure against the plastic film for exactly 3.0 s, and retract automatically without the user touching any other control.

1. a) Justify why a conventional bistable valve actuated by two manual push buttons does not solve this specification.
2. b) Design the circuit by describing the operation of an on-delay pneumatic timer: explain which three elements make it up (one-way flow control valve, reservoir or accumulator, and pneumatically piloted 3/2 valve) and what physical principle generates the time delay.
3. c) Predict what would happen to the sealing time if the network pressure suddenly drops from 6.0 bar to 3.5 bar while keeping the same setting on the throttle screw. Justify your answer.

In a factory producing paints and flammable solvents (an area classified as a deflagration risk environment), pneumatic and electric actuators are being compared for a pigment dosing gate.

1. a) If the gate suffers an unexpected mechanical jam due to caking of the material, predict and compare what will physically happen to a conventional electric motor and to a pneumatic cylinder if both continue to receive power supply for several minutes (analyse internal temperature, power consumption, and fire risk).
2. b) Explain why the use of pneumatically piloted valves eliminates the inherent danger of electrical relays and contactors in this environment.
3. c) Despite its advantages, compressed air flowing at high speed through insulating plastic pipes can pose an explosion risk. Explain what physical phenomenon occurs and what technical measure must be adopted in the installation to neutralise it.

The compressed air network of a school workshop supplies six workstations. After one month of operation, three serious failures occur: condensed water enters the valves rusting the spools, pressure drops sharply when three workstations operate simultaneously, and the noise level in the classroom exceeds permissible limits.

Upon inspecting the installation, it is found that:

• The main pipe was installed completely horizontally, and the branch lines to the workstations come out from its bottom part.

• There are no intermediate condensate drains.

• There is only one centralised service unit (FRL) at the compressor outlet and none at the workstations.

• The valve exhausts discharge directly into the ambient air.

1. a) Explain the thermodynamic cause of the appearance of water and justify how the layout of the main pipe must be modified (longitudinal slope and gooseneck design of the branch connections) to remove liquid water.
2. b) Justify what specific auxiliary components must be incorporated into the exhausts and at each individual workstation to solve the problems of pressure fluctuation and noise pollution.