Improved swivel connector handles liquefied gases

DN Staff

June 24, 1996

4 Min Read
Improved swivel connector handles liquefied gases

Newbury Park, CA--Walter Smith is an engineer who doesn't know how to leave well enough alone--and his customers thank him for that. Inventor of the SMAC-1, the first LP-GAS delivery hose-end swivel to meet Underwriters' Laboratories (UL) standards, Smith decided to be proactive and improve his design amidst little competition and few complaints. The result: the JO-1, a smaller, lighter, and equally robust swivel that costs less to manufacture.

It builds on the foundation established by the original SMAC-1, a design conceived in a trade-show hotel room in 1992. Walter's company, Smith Precision Products, produces sealed rotary pumps, and a customer challenged him to apply his sealing technology to a virgin field: swivels for LP-GAS delivery hoses. "Turns out that nothing had ever been successfully listed with the UL for LP-GAS," says Smith. "But at the time, I didn't even know what a swivel connector was."

The SMAC-1 proved so successful that Smith spun off another company, Full Circle, to make them. The first month alone they logged 5,000 orders. Yet a couple of customers hinted that the swivel was bulkier than they'd like. It measured 63/8 41/8 inches and weighed 2.75 lbs. Some mentioned that the aluminum housing might corrode when exposed to road salt. Others noted that should the swivel accidentally drag on the pavement behind the delivery truck, the aluminum wouldn't take the abuse.

Valid comments, all. But none was greatly hampering sales. What really drove Smith was his engineer's desire to build a better swivel and optimize an overly robust product. "There was no real problem," says Smith, "I just wanted to see how far we could push the design."

He had donned his pump-designer's hat while engineering the original SMAC-1. It contained dual ball bearings rated for radial loads of 2,500 lbs each at 33 rpm, and a three-piece seal developed for a lifetime of high-speed use--overkill for a hose swivel. The coil preload spring was a large space consumer, as was the three-piece seal.

Yet any new design still had to meet UL 567. Several of UL's tests are brutal, simulating lifetimes of abuse. In an endurance test, for instance, technicians pressurize the swivel to 250 psi, hang a 25-lb weight from its end, and rotate the joint through 180 degrees 100,000 times. They then take the same swivel and pressurize it to 600 psi and look for leaks. Smith's SMAC-1 was the first to pass the tests.

The breakthrough for the JO-1 came from an advertisement by the Smalley Steel Ring Co. (Wheeling, IL) that Smith spotted in Design News. He felt their wave spring could, in combination with a shorter seal and one less bearing, dramatically reduce the size of the swivel. "In the end, we wound up using four Smalley products in the JO-1," says Smith.

One wave spring replaces the coil compression spring. As part of a pending patent, Smith relocated it from the end of the seal stack to inside the rotating nipple. A second wave spring acts against a thrust plate and provides a 0.010-inch cushion for the bearings should the swivel get dropped on its nose--also a patent-pending feature.

Now made of stainless steel, the housing assembles using a Smalley retaining ring instead of Allen screws. Eliminating the flange for the screws saved weight, and the unit can be field-serviced with a screwdriver. A simple O-ring seal prevents water intrusion and corrosion around the nipple.

Smith also changed the gas seal from an unbalanced three-piece design to a balanced two pieces that require less force to rotate at 400 psi than the old one did at 200 psi. It consists of a continuous-cast gray-iron seal mated to a seal ring made of a monomeric thermoplastic. The faces of both are lapped to three light bands, even though the supplier of the plastic rings says the material can't be lapped at all.

Compared to the SMAC-1, the shorter seal design saves space. One fewer lapping operation and the elimination of a bearing and plating cuts $20 from the JO-1's cost.

Final verdict: The JO-1 weighs 1.50 lbs and measures 33/8 inches long--roughly half the figures of its predecessor. It's now completely corrosion-resistant, contains fewer parts, operates more easily at high pressures, and is field serviceable.

Additional details...Contact Walter Smith, Full Circle, Inc., 1299 Lawrence Drive, Newbury Park, CA 91320, (805) 498-6616.

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