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The world’s railroads cover millions of miles and provide an unbeatable combination of speed and economy in transporting goods. A single freight train contains dozens of cars, so a component malfunction can potentially delay shipment of millions of dollars worth of goods. It should be no surprise, then, that pneumatics is widely used throughout the rail industry due to its long-term reliability, even in the face of adverse conditions.
Electrical connectors are not real forgiving because they can break, pull loose, or corrode to the point where they lose contact. Pneumatics, on the other hand, is rugged enough to tolerate the extreme temperatures, shock, vibration, moisture, and corrosive atmospheres encounted every day in the rail industry.
Down the Hatch
One area that extensively uses pneumatics is the actuation of hatches and cargo doors. Routing compressed air to the rod end of a double-acting cylinder will cause it to retract every time. Likewise, routing air to its cap end makes it extend. But losing supply pressure can allow an external load acting on the cylinder’s piston rod to move it.
The traditional solution to this problem uses two cylinders: a main cylinder to actuate the device, and a second single-acting cylinder to extend a locking pin to prevent the main cylinder’s piston rod from moving. IMI Precision Engineering stepped in to improve this setup, and the company’s prowess led to the introduction of Norgren’s latching cylinders—they keep a retracted rod retracted and an extended rod extended, even when supply pressure is lost.
An important design aspect of latching cylinders is that they are no larger than a standard cylinder. This makes it easy to retrofit into existing applications. They also feature modular construction, enabling them to be quickly built from standard components to serve a particular application.
Out with the Old
Traditionally, one actuator moved the load, and a second locked the main actuator in place. However, Norgren’s latching cylinders require only a single control valve to fulfill all of these functions. Its latching cylinders reduce the number of components used, space, weight, and installation time, as well as ease maintenance.
The piston rod has a recess on its OD that lets a spring-loaded pin lock the rod into place once it is fully retracted. Compressed air supplied to the cap end of the cylinder overcomes spring force and pushes the pin out of the recess so that the rod can extend. Likewise, once the piston rod reaches full extension, a second pin at the rod end engages a second recess in the rod to lock it in place once it reaches full extension. Routing compressed air to the rod end of the cylinder pushes the pin out of the recess, enabling the piston rod to retract.
Mark Wrigley, Western Europe Market Director at IMI Precision Engineering, explains, “We have worked closely with our customers to understand their needs, resulting in products being developed in different bore sizes for a range of applications. By creating tailor-made solutions for individual customers, we know our products will guarantee improved speed, productivity, reliability, and efficiency. We integrate the latching system into specially modified end caps of our ISO RA/8000 series cylinders without altering the envelope dimensions, so it can be used with other ISO/VDMA cylinders. The latch also has a knob or threaded shaft to unlock the cylinder as a manual override, if so required.”
Norgren’s latching cylinders are dimensionally interchangeable with NFPA 1000 and IS/VDMA 8000 series cylinders, and come in standard bores of 5 in., 6 in., and 32, 40, 125, and 200 mm.
For more information on products and services from IMI Precision Engineering, Littleton, Colo., call (303) 794-2611, or visit www.norgren.com/us.