Compact actuator delivers high level of torque, force
Oden Control has launched a new Atex-certified, DNV-tested actuator for offshore duty - the P30EX series. It is a compact, modular unit based on the company’s patented eccentric gear.
At the heart of the design is the unique Oden Gear System, developed by the company’s technical manager Gustav Rennerfelt, which comprises two gears and an eccenter. The actuator is powered by a 24V DC electric motor with integrated electronic control.
The input motor shaft has an eccentric tap with a ball bearing and an inner gear meshing a stationary internal gear. When the input shaft is rotated one turn, the inner gear rotates one tooth pitch in the opposite direction if the difference in the number of teeth is one. This gives an exceptionally high gear ratio in one step - in the P30EX there are 64 teeth at the inner gear and 65 teeth at the stationary internal gear, resulting in a ratio of 64:1 in one step. Other larger Oden actuators, which are not yet ATEX certified, have 100 and 101 teeth respectively, giving a ratio of 100:1 in one step. Gear designs are under development for a ratio of 250:1.
Oden's Atex-certified actuator P30EX provides a compact, efficient, and lightweight solution for offshore duty.
A simple and reliable solution is used to transmit the slow eccentric rotation of the inner gear to a centric rotation on the output shaft. The inner gear consists of a cylindrical ‘pipe’ with a slightly conical gear placed at one end and an internal coupling at the other. The inner gear makes a conical movement around the center point of the coupling. The total gear efficiency of the system is higher than 90%.
For its size and weight, the P30EX series provide a powerful level of torque and force:
• The P30EXR1 turning actuator, 270 mm long, 104 mm in diameter, and weighing 3 kg, delivers 30 Nm torque
• The P30EXH actuator for quarter-turn valves, weighing 22 kg, delivers 2,500 Nm torque and has a closing time of 45 seconds for a quarter turn
•The P30EXL1, a high-speed linear actuator, which is 350 mm long, 104 mm in diameter, and weighs 5 kg, delivers 12 kN force.
The simple construction, light weight, and small dimensions of the Oden product are advantageous in the context of an offshore platform where space and weight are at a premium. In these respects, it compares well with other types of actuators, such as pneumatic systems, which require compressors, pressure tanks, air filters, air dryers, and stainless steel piping; hydraulic systems involving pumps, oil tanks, and hoses, which are often subject to leakage; and electro-mechanical systems based on low-efficiency gears.
For DN600 valves, Oden also offers the High Torque Gear for 30,000 Nm torque applications. Compared with a conventional actuator, typically 1.5 m high and weighing up to one ton, this unit is 600 mm high and weighs less than 200 kg.
Installation freedom
The design of the actuators enables them to be mounted in any direction without causing any problems for the lubrication in the gearbox. It also avoids the classic problem associated with conventional actuators of having to be carefully aligned with the valve spindle.
“With our product, any misalignment is taken up by the coupling,” says Rennerfelt.
Having few parts, the maintenance requirement is low. The company recommends a function check once every three years, compared with the annual check required for most conventional actuators. The simple construction means that parts can be changed out in 10 minutes or less.
Self-calibrating
The actuator’s electronic control also brings benefits. When the actuator is first fitted to the valve, it is programmed to calibrate itself by operating the valve to find the closed position, and is then ready for action. The customer decides parameters such as the control speed, and can easily change them with the aid of the Oden Valve Control program. Settings can be prepared in the office and downloaded at the actuator.
A unique solution has been found to the problem induced by hot media, which may cause the valve - when in the closed position - to become stuck as the pipe shrinks. A feature is included in the control software, whereby the actuator makes a small movement of the valve every 20 minutes to ensure free movement. By contrast, some conventional actuators are over-dimensioned to give them sufficient torque to move a stuck valve.•
For more information, contact Helena Granqvist or Gustav Rennerfelt, Oden Control. Tel +46 8767 7657, fax +46 8767 4718, [email protected], www.odencontrol.se.
