Data Sheet for Product

Powers™ Controls

Technical Bulletin

Document No. 155-219P25

TB 181

March 2, 2005

Maximum Thrust Ratings of

Pneumatic Damper Actuators

Siemens Industry, Inc.

Description

Actuator force or thrust is expressed in total net pounds of force available at the actuator

shaft. This force can be modulated to an intermediate value to maintain a stabilized

position against a known load, or increased to initiate a forward or return thrust to

activate the operated device to a new position. The net available force in either direction

is always the difference between the spring force at that actuator position and control

pressure times the diaphragm area.

The values expressed in the following tables are the maximum forces available at

various actuator positions, using either full supply air or the full available force of the

actuator spring. Positioning type control devices can use up to the full supply air

pressure to stabilize or to initiate a forward movement of the actuator shaft. Return

movement depends on the internal spring force exceeding the workload at any actuator

position.

Torque Ratings

Rotary force requirements are expressed in terms of torque. Dampers and associated

linkages are normally rated in this manner. Torque is usually expressed in terms of

pound-inch, pound-foot, or Newton-meter.

Actuator thrust can be converted to torque by the following formulas:

• Multiply pounds force by effective crank radius in inches to obtain pound-inch.

• Multiply pounds force by effective crank radius in feet to obtain pound-foot.

• Multiply Newtons by effective crank radius in meters to obtain Newton-meters.

The effective crank radius is less than the actual crank radius because the effective

force exerted by the actuator decreases as the angle between the crank and actuator

shaft decreases from 90°. The effective crank radius used for these tables is equal to

the crank radius for 90° rotation (See Figure 1) times 0.5 (sine of 30°). This assumes a

“worst case” actuator mounting which has the crank at 30° to the actuator shaft when

the actuator shaft is fully retracted. The recommended actuator mounting should have

the crank at 45° to the actuator shaft when the shaft is fully retracted.

Torque ratings are based on crank radius for 90° damper rotation. For ratings other than

90° rotation, multiply by the ratio of (Crank radius at X° / crank radius at 90°). See

Figure 1, to determine crank radius.

PAGE 1
Technical Bulletin Document No. 155-219P25 TB 181 March 2, 2005 Powers™ Controls Maximum Thrust Ratings of Pneumatic Damper Actuators Description Actuator force or thrust is expressed in total net pounds of force available at the actuator shaft. This force can be modulated to an intermediate value to maintain a stabilized position against a known load, or increased to initiate a forward or return thrust to activate the operated device to a new position.
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Technical Bulletin Document Number 155-219P25 March 2, 2005 Maximum Thrust Ratings of Pneumatic Damper Actuators Using This Graph To find the required stroke when the crank radius is known: 1. Select available crank radius at the left of the graph. 2. Follow the curved line to the intersection with the degree of rotation desired. 3. Follow the vertical line down to read the required actuator stroke. To find the crank radius when the stroke is known: 1.
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Maximum Thrust Ratings of Pneumatic Damper Actuators Technical Bulletin Document Number 155-219P25 March 2, 2005 Table 1. No. 3 Damper Actuator with 2-3/8 inch Stroke.
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Technical Bulletin Document Number 155-219P25 March 2, 2005 Maximum Thrust Ratings of Pneumatic Damper Actuators Table 2. No. 4 Damper Actuator with 4-inch Stroke.
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Maximum Thrust Ratings of Pneumatic Damper Actuators Technical Bulletin Document Number 155-219P25 March 2, 2005 Table 3. No. 6 Damper Actuator with 4-inch Stroke.