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TRANSMISSION MECHANISM
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n° 8_0084 TRANSMISSION MECHANISM OMAL S.p.A. Via Ponte Nuovo 11 - 25050 RODENGO SAIANO (BS) ITALY Tel. 030/8900145 r.a. - Fax 030/8900423

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All data and specifications in this manual may be changed at any time and without prior notification to improve our products. They cannot be considered binding.

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MAIN FEATURES Every OMAL pneumatic actuator features a special system which converts the linear motion of the pistons operated by pressure into the rotational motion of the output shaft. OMAL pneumatic actuators differ from all other pneumatic actuators on the market where the motion is converted through the engagement of a rack on the pistons with a pinion on the shaft which generates a steady output torque regardless of the piston position or the shaft angle. Pinion Slot Rack OMAL actuator “Scotch Yoke” mechanism Rack & Pinion system OMAL “Scotch Yoke” design provides the actuator with an...

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COMPARISON WITH RACK & PINION ACTUATOR Torque Torque CURVE 2: Rack & Pinion actuator with the same torque as the minimum torque value in an OMAL actuator (not enough to operate the valve with torque as per curve 1). CURVE 4: Rack & Pinion actuator with the same torque as the maximum torque value in an OMAL actuator (having the same safety factor when it starts operating the valve). The actuator looks way too big with consequent waste of energy and pressure (the broken line represents the energy that OMAL actuators can save). CURVE 3: OMAL pneumatic actuator The curve shows how the actuator...

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HOW TO CALCULATE THE TORQUE VALUE IN AN OMAL ACTUATOR Fp = Force applied on the piston by air Closed position 0° (open pistons) Mt = Torque value D = Cylinder nominal diameter P = Air supply pressure Position 50° Dati: Open position 90° (closed pistons) D = 100 mm P = 5,6 bar = 0,56 N/mm2 Fp= (ΠD2)*P/4 = 4398 N Taking OMAL pneumatic actuator model DA480 as an example, we will calculate the torque values with the output shaft in three different positions (0°, 50° and 90°). Position 0°: Mt = 2*(Fp/cos(56°))*42,17 = 663326 Nmm = 663 Nm NOTE: The vertical factor V does not affect the torque...

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SPRING RETURN ACTUATORS The above applies to DA actuators but can also be extended to OMAL pneumatic SR actuators. The slot on the latter is 90° off the position of the slot on the former to facilitate the closing of the pistons (rather than the opening) which happens through the release of special springs (in SR actuators the closed valve position corresponds to the closed piston position contrary to DA actuators). The propulsive force of a progressively releasing spring gets gradually smaller but, thanks to a special mechanism, the torque curve still increases before getting to the end;...

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