Double acting quarter turn actuators

General operating principle of a doudble acting actuator

Air to por t A forces the pistons outwards, causing the pinion to turn counterclockwise while the air is being exhausted from port B.

Air to port B forces the pistons inward, causing the pinion to turn clockwise while the air is being exhausted from port A.

Air to port A forces the pistons outwards causing pinion to turn clockwise while the air is being exhausted from port B.

Air to port B forces the pistons inwards,causing the pinion to turn counterclockwise while the air is exhausted from port A.

Sizing a double acting actuator

To size a double acting actuator there are different parameters important to be known

Breakaway torque of the process valve

The torque required to facilitate

reliable opening of the valve’s shut-off device(disk in a butterfly valve, ball in a ball valve…)under the specified operating conditions(medium, temperature, inline pressure, etc)

Compressed air supply

The minimum compressed air pressure available at aII time at the valve to be sized forms the basis for sizing(worst—case analysis).

Process valve type

What type of

valve(butterfly valve,ball valve,etc) is being used?

The main operating conditions must be known before the breakaway torque

can be specified by the valve manufacturer orcorrectly derived from

existing tables.

-Medium

-Temperature, concentration, viscosity of the medium.

-Gas or liquid, lubricating or nonlubricating.

-Presence of particles that from deposits or caking

-Differential pressure at the process valve.

-Required safety factor.

If no safety factor is specified, a factor of at least approx.1.25(25%safety) should be taken into account when sizing the quarter turn actuator.

0○=Valve closed

90○=Valve open

Md1=Breakaway torque

Md2=Closing torque

Sizing Example：

Data given:

1.Air pressure: 6 bar

2.Breakaway torque: 100 bar

3.Safety factor: 25%

Relationship of the actuator to the butterfly valve torque curve

This give a minimum torque of 125Nm for the quarter turn actuator. The Torque tables for double acting quarter turn actuators propose the actuator with the designation EP-110-DA. This actuator has a torque of 136.4Nm at compressed air pressure of 6 bar.

This torque is constant across the entire swivel range(0○-90○) thanks to the rack and pinion design and is therefore sufficient for the valve.