How to Installation And Maintenance of Scotch Yoke Pneumatic Actuators ?

What is a Scotch Yoke Pneumatic Actuators and what is a pneumatic actuation system?

Hearkenflow produces a wide range of pneumatic actuators, with “Scotch yoke” mechanism, for valve drive and remote control. Such pneumatic actuators are available both in the double acting “DA” version and in the Single Acting “SA” version.

This system provides a long life for the pneumatic actuators and the best performance, with the least energy consumption….

Hearken Scotch yoke system has a torque curve that makes the maximum torque available right at the breakaway of the valve, the initial opening moment.

What is a pneumatic actuator used for?

Pneumatic actuators operate by using compressed air to move a piston or diaphragm, which in turn drives a mechanical load. They are often preferred over other types of actuators (such as hydraulic or electric) because they are simple, reliable, and relatively inexpensive.

Some common uses of pneumatic actuators include opening and closing valves in pipelines and processing plants, controlling the movement of robotic arms in manufacturing operations, and powering door and gate opening mechanisms. They can also be found in a variety of consumer products, such as air compressors, power tools, and pneumatic nail guns.

What is actuator in pneumatic system?

Double Acting (DA) Actuator :

For clockwise to close valves, pressure to the right port closes the valve, pressure to the left port opens the valve.

Single Acting (SA) Actuator :

For clockwise to close valves, pressure to the right port closes the valve (Normally opened) or opens the valve (Normally closed). The left port is an exhaust port from the spring chamber(s).

Specification Of HPAC Scotch Yoke Pneumatic Actuator

Mounting flange according to：UNI EN ISO 5211

F03-F04-F05-F07-F10-F12-F14-F16-F25

Conforms to UNI EN 15714-3:2009 standard

Accessories connection：NAMUR

Rotation angle: 90°.Exactly adjustable between -8°/+3°

Working temperature：0℃~80℃，-20℃~80℃（Filtered compressed air dry）.（special version：high temperature：-20℃~120℃；low temperature：-50℃~60℃

Supply pressure: min. 2,5 bar, max. 8 bar

Working medium：Filtered compressed air

In the case of air lubrication, do not use detergent oil or lubricating oil compatible with NBR

Safety Information of Scotch Yoke Pneumatic Actuator

- Hearken pneumatic actuators must be used within the specified pressure limits, operation beyond these limits may damage the internal parts of the actuator.

- The pneumatic actuators operation out of the range of temperatures indicated could damage its internal or external parts.

- Using the actuator, without the due external protection, may damaged it in corrosive environments.

- Before the installation, repair or maintenance be sure that the pneumatic actuator is not pressurized, disconnect the air lines and verify that they have vented.

- Do not remove the covers when the pneumatic actuator is installed online or while it’s still pressurized.

- Do not remove the spring cover, this operation may be carried out by qualified personnel only; such operation could cause personal injuries.

- Before installing the actuator on the valve be sure that the rotation of one is in phase with the rotation of the other and that the shaft slit position is correct.

- Before installing the actuated valve, carry out a few dry cycles in order to check the proper fitting between valve and actuator.

- Carry out the installation in compliance with the national local regulations and laws.

Actuator Outside View 

Double Acting DA version:

Closed

Opened

Single Acting SA version:

1. normally closed: 

Closed

Opened

2. normally opened: 

Closed

Opened

Stroke adjustment of the actuator

The stoke adjustment of the actuator, that is mounted on the valve, must be carried out with the valve free from pressure or any other frictions. Furthermore, the actuator must be disconnected from the air supply. This operation must be done when the valve / actuator is secured in the system or in a clamp.

a. Instructions for Double Acting DA version. Closing stroke adjustment from -3° to 8°

• - Apply air pressure to port A to open the valve, and to position the actuator pistons inward.
• - Remove the cap nuts (ref.1) and the O-rings (ref.2).

       

• - Rotate the adjustment screw in a clockwise direction (ref.3) only on one side of the actuator in order to stop the piston stroke before the 90° available, therefore identifying an early “valve closed” point.
• - Apply air pressure to port B so to position the pistons outward, therefore resting on the adjustment screw and check the valve closing position.
• - If the valve position is not correct repeat the process over again.
• - On the contrary, when applying air to port B, if the valve is not sufficiently closed, unscrew the both adjusting screws in the counterclockwise direction (ref.3) until the desired position is found.
• - Once the right valve position is obtained, while applying pressure to port B screw the adjustment screw located on the other end until it rests against the piston. This way both the adjustment screws will stop the pistons at the same time.
• - Tighten the cap nuts (ref.1) with the O-rings (ref.2) in order to fasten the adjustment screws in the desired position.
• - The actuator is now ready to function properly.
• The Hearken actuator standard adjustment is maximum 11 °, special length screws are available upon request.

b. Instructions for normally closed Single Acting SA version. Adjustment of the opening stroke from 82 ° to 93 °（The same adjustment method for the closing stroke of normally opened actuators）

• - Remove the cap nuts (ref.1) and the O-rings (ref.2).
• - Rotate the adjustment screw in a clockwise direction (ref.3) only on one side of the actuator.
• - Apply air pressure to port B so to position the pistons outward, up to the limits determined by the adjustment screw located on the piston head.
• - Check the valve open position, if it’s too open repeat the process over again.
• - On the contrary, when applying air to port B, if the valve is not sufficiently open, unscrew the both adjusting screws in the counterclockwise direction (ref.3) until the desired position is found.
• - Once the right valve position is obtained, while applying pressure to port B screw the adjustment screw located on the other end until it rests against the piston. This way both the adjustment screws will stop the pistons at the same time.
• - Still while air supply under pressure, tighten the cap nuts (ref.1) with the O-rings (ref.2) in order to fasten the adjustment screws in the desired position. The actuator is now ready to function properly. 
• The Hearken actuator standard adjustment is maximum 11 °, special length screws are available upon request.

Trouble Shooting Of Scotch Yoke Pneumatic Actuators

PROBLEM	POSSIBLE CAUSE	SOLUTION
Loss or reduction of the sup-plied torque	Lack of supply	Verify that the pneumatic actuator has been connected to the pneumatic line correctly
	Air supply not enough to produce the required torque	Verify that the supply pressure value corresponds to the functioning requirements (See actuator data plate).
	Air leakage from the seals	Verify that the screws are completely tightened
Leaks from the stem upper or lower seals	Stem O-ring seal damaged	Replace the seals
	Damages on the body	Contact Hearken for repair
	Shaft damaged
Leakage from cylinder caps	Seals damaged	Replace the seals
Leakage from the ports after maneuver	Piston sealing damaged	Replace the piston seals
	Cylinder body damaged	Contact Hearken for repair
Insufficient rotation angle	Increase of valve maneuver torque	Verify the valve release torque and possibly replace with a new one
	Air supply not enough to produce the required torque	Increase the air supply
	Mechanical stop (if there) not duly adjusted	Adjust the stops by increasing the stroke
	Wrong connection between the pneumatic actuator and the valve stem	Check the connection elements between the valve and the actuator