January 13, 2014
Need to connect a flexible hose to a rigid metal nipple? The worm gear clamp has been the standard for decades, but they aren’t ideal for the soft, thin-wall tubing used in aircraft environmental control systems.“Build a better mousetrap, and the world will beat a path to your door” is little more than a cliché, but nevertheless it handily sums up the spirit of innovation that drives entrepreneurs to create new products and improve existing ones. It’s also a reminder that an invention or an improvement doesn’t have to be earth-shattering to make a difference. Even an improvement on the humble mousetrap is noteworthy if it catches more mice.
Like the mousetrap, the worm gear hose clamp isn’t a high-profile item, but it is a critical automobile component. It has been used for securing automotive radiator hoses for decades, and this application is a good match for this clamp. It is simple to install and remove, holds the hose in place securely, and withstands the normal operating pressure of a typical cooling system, around 15 pounds per square inch. Made from stainless steel, it typically outlasts the car itself. This clamp also made its way into the aircraft industry, where it often is used on environmental control system (ECS) hoses. For this application, the common hose clamp is less than ideal.
“Aircraft ECS hose is made from thin-wall silicone, which is softer and thinner than automobile radiator hose,” said John Fritskey, vice president of engineering of Voss Industries, Cleveland. “When a worm gear clamp is used on an ECS, it often doesn’t seal all the way around the circumference. One of our customers reported that it sealed about 300 degrees around the hose.” A bad seal around 15 percent of the circumference might not sound like much, but an ECS has dozens of such connectors, causing it to operate well below its intended capacity.
The other problem is that the edges and notches in the ring dig into the hose. While this might actually be an advantage for a radiator hose, providing a secure grip, it’s anything but beneficial on ECS hose. To save weight and therefore fuel, aircraft designers use the least amount of material possible on every component, so thin-wall ECS hoses are damaged easily by common hose clamps. The normal stresses and vibrations incurred by aircraft accelerate the wear, decreasing the hoses’ service life.
“The Perfect Seal uses a flared band, so it doesn’t cut into the hose,” Fritskey said.
The next problem was friction. A common worm gear’s screw, which is in a housing, is threaded into the band’s notches; as the user tightens the screw, it develops quite a bit of friction. “It’s hard to know how much torque you’re applying when you’re tightening one of those clamps,” Fritskey said. He added that the friction can cause the hardware, which is stainless steel, to heat and bind. In some cases, the heat is so severe that the parts bind permanently. The Voss product uses a silver-plated screw to prevent friction and galling. It can be tightened an unlimited number of times, Fritskey said.
Voss engineers solved the problem of the incomplete seal by eliminating the screw’s housing, which causes a flat spot on the clamp’s diameter. The screw tightens by drawing two tabs toward each other, tightening the band like a belt.
Voss added a few other features that make the user’s life easier. First, it has a quick-release mechanism, so the user can save a lot of time when removing it. Second, the screw locks in the barrel nut, so it can’t back out on its own. Third, the company peens (flares) the screw’s end after it is installed in the barrel nut, so it can’t get lost.
Certified for aircraft use, it has spot welds that comply with AWS D 17.2 (aerospace standard). Finally, it is available in several sizes and materials. Diameters run from 1.50 to 10 in. (in 0.125-in. increments), and the band is available in two widths, 0.3125, and 0.375 in. Standard materials are 301 1/2H stainless steel, 316 stainless steel, 625 nickel, and 6-4 titanium. It’s also available in materials that comply with Defense Federal Acquisition Regulation Supplement (DFARS).
Although it is a new product, released in 2013, it already is specified for use by aircraft systems manufacturers Rolls-Royce and Liebherr, Fritskey said. Does it have other uses? Voss has seen it used to secure antennas, and Rolls-Royce has specified it for use on a metal-to-metal tube connection.
Fritskey doesn’t predict widespread adoption in the automotive industry. The standard worm gear clamp works well and costs less. However, Fritskey thinks it might work well in some niche automotive areas, perhaps racing, because it doesn’t have sharp edges.
“Nobody wants to lose a race because of a blown radiator hose,” he said.
Voss Industries Inc., 2168 W. 25th St., Cleveland, OH 44113, 216-771-7655, www.vossind.com
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