Controling of Pneumatic Cylinders

Pneumatic cylinders can be controlled by the following methods:
1. Direct control of Single or Double acting cylinder
2. Indirect Control of Cylinder with Single Piloted Final Control Valve
3. Indirect Control of Cylinder with Double Piloted Final Control Valve
In the indirect control actuation, a pilot signal from a 3/2 N.C. valve is used to activate pilot ports of final control valve.

Controlling of Pneumatic Cylinders

Controling Of Pneumatic System

Direct Control of Single Acting Cylinder

Direct Control Of  Single Acting Cylinder

Pneumatic cylinders can be directly actuated by actuation of final control valve, manually
or electrically in small cylinders as well as cylinders which operates at low speeds where
the flow rate requirements are less. When the directional control valve is actuated by
push button, the valve switches over to the open position, communicating working source
to the cylinder volume. This results in the forward motion of the piston. When the push
button is released, the reset spring of the valve restores the valve to the initial position
[closed]. The cylinder space is connected to exhaust port there by piston retracts either
due to spring or supply pressure applied from the other port.

Indirect Control of Single Acting Cylinder

Indirect Control of single and double acting cylinders

Large cylinders as well as cylinders operating at high speed are generally actuated
indirectly as the final control valve is required to handle large quantity of air. In the case
of pilot operated valves, a signal input valve [3/2 way N.C type, 1S1] either actuated
manually or mechanically is used to generate the pilot signal for the final control valve.
The signal pressure required can be around 1-1.5 bar. The working pressure passing
through the final control valve depends on the force requirement [4-6 bar]. Indirect
control as permits processing of input signals.
Single piloted valves are rarely used in applications where the piston has t o retract
immediately on taking out the set pilot signal -.suitable for large single acting cylinders.

Use Double Piloted Valve

Double piloted valve [Fig 3.3] is also called as the Memory valve

With the actuation of Forward push button, the out put signal activates the set pilot port
[14] of final control valve. This results forward motion of the cylinder
Now even if this push button is released the final control valve remains in the actuated
status as the both the pilot ports are exposed to the atmosphere pressure and the piston
remains in the forward end position.

Use of double Piloted Valve

In order to retract the cylinder, the Return push button is activated. This will convey reset
signal from signal source to the pilot port of final control valve [12] . The piston retracts.
Now even if the Return push button is released the status of the cylinder will not change

Methods of Checking The End Positions

The following methods are commonly used to interrogate the end positions of piston in

the cylinder:

1.Mechanically operated limit switches ( Roller lever or idle return roller type)

2. Reed sensors, either with electrical or pneumatic out put [the piston is incorporated

with ring magnet]

3. Electrical proximity switches

4. Pneumatic Signal generators

Use of Limit Switches

•S1 and S2 are the limit switches corresponding to home position and extended position
•Although they are located in the path of the movement of piston rod, normal practice is
to represent the symbol of the limit switches on either side of the final control valve
with out put signals connected to the pilot ports of the valve. The limit switches of Roller
lever type are essentially 3/2 way ball seat or disc seat type of valves handling pneumatic
signals. These are available with direct actuation type and internally pilot actuation type
versions. Limit switches of idle return roller type are used for actuation only in one
direction are used as signal elimination device in case of signal overlap.

Use of Mechanically operated Roller lever Limit Switches

Pin Feeding Device

Pins are to be fed from a hopper to the next station one at a time using a
Pneumatic Cylinder. Speed of the cylinder should be adjustable both during forward and
return motion. The process of feeding should be initiated using a detent push push
button. Develop a suitable Pneumatic control circuit .

Pin Feeding Device

Pin Feeding Device

Rotary Indexing Table

Cans are required to be transferred from one conveyor to the other through a
filling and capping station. A rotary indexing device is used which should be able to
operate using a pneumatic cylinder with ratchet arrangement. The process should start on
actuation of a push button operated valve. The process should stop when no cans are
present from the incoming conveyor. The can sensor can be roller lever type of limit
switch . Draw a suitable pneumatic control circuit.

Rotaty Indexing Device

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