control of a double-acting pneumatic cylinder

CONTROL OF A DOUBLE-ACTING PNEUMATIC CYLINDER

1. Direct Control of a Double-Acting Pneumatic Cylinder

1. Circuit

Fig.13.3 illustrates a circuit that can be used to control a double-acting air cylinder. This circuit has a push-button operated 5/2 DC valve and a double-acting air cylinder.

2. Operation

Extension : When the push-button is activated (i.e., pressed), the 5/2 DC valve is shifted to bottom envelope flow path configuration. So the compressed air flows into the blind end of the cylinder and hence the cylinder extends. At the same time, the air at the rod end of the . cylinder is exhausted directly to the atmosphere.

Retraction: When the push-button is deactivated (i.e., released), the 5/2 DC valve is shifted to spring-offset mode. Now the compressed air flows into the rod end of the cylinder and hence the cylinder retracts. At the same time, the air at the blind end of the cylinder is exhausted directly to the atmosphere.

2. Air Pilot Control of Double-Acting Cylinder

(Indirect Control of Double-Acting Cylinder using Memory Valve) 

1. Circuit

Fig.13.4 illustrates a circuit that employs air pilot-actuated DC control valve to control a double-acting air cylinder. The air pilot-actuated valve enables to operate the double-acting cylinder remotely. This circuit has two push-button operated 5/2 DC valves and a pilot- actuated DC valve. It may be noted that double pilot-actuated DC valve is called memory valve.

2. Operation

This circuit uses low-pressure (P1) (say, 10 psi) push-button DC valve to actuate pilot- operated DC valve to obtain the required high-pressure (P2) (say, 100 psi) air flow to the cylinder.

Extension: When the push-button of valve V1 is pressed and valve V2 is in its spring- offset mode, the low-pressure (P1) air in valve V1 gives pilot signal to pilot-operated DC valve PV. This enables the supply of high-pressure (P2) air to the blind end of the cylinder and hence the cylinder extends. The rod end air is exhausted to the atmosphere and this position is retained till the pilot signal from the valve V2 is obtained.

Retraction: When the push-button of valve V1 is deactivated (i.e., released) and the push- button of valve V2 is activated, the valve V2 gives pilot signal to pilot-operated DC valve PV. This now enables the supply of high-pressure (P2) air to the rod end of the cylinder and hence the cylinder retracts.

In the above circuit, it may be noted that after pressing the push buttons of V1 and V2 for the respective strokes to take place, and after release of push buttons the valves come back to initial spring offset mode positions. This allows acceptance of pilot signal and activation of PV so that the other side of pilot signal is exhausted through V1 and V2 to the atmosphere. Also, even after V1 and V2 are released to return to their initial spring offset mode positions, the pilot signals once sent are memorized and accordingly performs the desired piloting function.

3. Control of Double-Acting Cylinder using Shuttle Valve

1. Circuit

Fig.13.5 illustrates a circuit that employs shuttle valve to control a double-acting air cylinder. The shuttle valve, also known as OR gate valve, is used when the double-acting cylinder needs to be actuated from any one of the two push buttons or with pressing both push buttons of DC valves.

2. Operation

Extension: When the push button of DCV1 or DCV2 is activated, the compressed air flows through the shuttle valve (i.e., OR gate). This compressed air is allowed to go through the 5/2 DC valve and the air flows into the blind end of the cylinder and hence the cylinder extends. At the same time, the air at the rod end of the cylinder is exhausted directly to the atmosphere.

Retraction: When the push-button of both DCV1 and DCV2 are released to the initial position, there will be no signal air to 5/2 DC valve and the spring of 5/2 DC valve puts back the original valve position and the cylinder retracts. At the same time, the air at the blind end of the cylinder is exhausted directly to the atmosphere.