Unique Seal Design for the Flex-Coil® Swivel System

The unique seal design in the Flex-Coil® Swivel System provides bi-directional sealing and 360° low friction swivel in IV devices used for medicating animals.

Delivering fluid through IV devices for medicating animals can be a difficult procedure for veterinarians. Our patented Flex-Coil® Swivel System makes the process safe and easy for the animal, as well as less labor intensive for the veterinarian.

The key to the Flex-Coil® Swivel System’s success is the unique seal designed by Minnesota Rubber and Plastics. It provides bi-directional sealing to contain and control fluid passing through a center pin that turns freely within the seal. The assembly provides 360° swiveling motion of the hollow center pin for free movement of the animal during treatment (Photo 1 and Illustration 1).

747 Photo 1 and Illustration 1: Unique seal design provides bi-directional sealing and 360° low friction swivel in the patented IV device from International WIN, Ltd.

Until the Flex-Coil® Swivel System was designed, administering fluids such as nutrients, blood, antibiotics, and other medications to dogs, cats, and larger animals such as foals and calves depended on unreliable and improvised devices. The most common problem was that with normal movement, the animal disconnected the IV and became entangled and/or chewed the tubing.

To administer continuous IV fluid, especially through the night, required continuous monitoring and repeated attention to the IV attachments to keep it working properly.

The Flex-Coil® Swivel IV System

The patented device consists of a series of tubes, coil, and connections that center and function from a mounted housing located above the caged animal patient. This housing snaps into and out of a “shoe” affixed to the top of the cage or holding area and contains the seal assembly that is the key to the overall function and success of the Flex-Coil® Swivel System (Photo 2 and Illustration 2).

Photo 2 and Illustration 2: The Illustration shows the Flex-Coil® IV system connected to a dog. The coiled tubing leads from the mounted housing that encloses the patented swiveling seal device designed by Minnesota Rubber and Plastics. Individual components that make up the seal assembly are pictured below.

Inside the housing, the seal and related assembly connects to coil tubing that connects to an IV catheter inserted in a vein and attached to the animal’s body. The coiled tube flexes easily when the animal moves and shifts position. Expanding and contracting, the coiled tubing allows free movement without becoming entangled with animal’s legs or body. Most important, the swivel device allows full 360° rotation without twisting, binding, or disconnecting the tubing. Fluid delivery continues uninterrupted at the prescribed rate.

The fluid bag or container (that contains blood, nutrients, antibiotics, saline, etc.) is attached to tubing (above and outside, or high in the cage or enclosure) and leads to the mounted housing. This keeps the fluid supply, infusion pump (when used) and the drip mechanism out of harms’ way and away from any movement that the animal might make.

What’s so clever about this device setup is that even if the animal becomes highly agitated and does a lot of jumping and twisting, the Flex-Coil® Swivel System keeps the animal clear of the coiled tube and IV connections. With this setup, the animal can’t see the IV attachment, bite at it or the coiled tube and thus leaves it alone.

Wider Use of Infusion Pumps & Longer IV Lines Created Seal Problems

“Coming up with the right seal was a real challenge when the technology for delivering IV fluids advanced about five years ago,” reports Dr. William Donawick, DVM and president of International WIN, Ltd., inventor of the Flex-Coil® system.

“Our original design had a one-way seal with minimal friction. It worked well for the times, but as more veterinarians included infusion pumps and longer tubing in their IV setups, the potential for problems arose. Use of infusion pumps occasionally created a negative pressure in the IV tubing causing dangerous air bubbles to enter. And when longer IV tube setups were used, gravity and distance also allowed small amounts of air to get into the IV. We had to find a seal to solve both of these leak conditions and one that also provided free 360° swiveling motion. It was that or discontinue the product.”

Minnesota Rubber and Plastics supplied the seals in the original Flex-Coil® Swivel System . Doctor Donawick said that he knew of the company’s long history in designing special application seals for unusual applications. “So we challenged them to see what they might recommend to replace the original seal,” he said.

“It was a monumental task because nothing quite like this had been done before. Chris Mauhar, design engineer for MR&P, saw this opportunity to do something really different. He and his team came up with the solution. The success of the Flex-Coil® Swivel System really depended on the function and reliability of that new seal design.”

Unique Bi-Directional Seal

“Dr. Donawick was an ideal customer to work with because he had a good sense of design and helped to overcome the design challenges,” reported Mr. Mauhar. “Together we recognized that conventional seals would not handle the opposing pressures in the IV line at the same time providing the needed 360° swiveling feature. Dr. Donawick envisioned a seal that worked with the squeegee effect of a windshield wiper blade’s alternating motion. Playing off that concept, we came up with a double lip seal design so that the lip facing up would contain the downward fluid (positive) pressure. The lip facing down would handle the upward fluid (negative) pressure.”

This was only half of the solution, however. The rotating hollow center pin (to allow fluids to pass through it) held in place by the seal, housing and cap of the assembly, had to swivel freely in a 360° motion without leaking when an animal patient pulled, twisted and turned the IV set. To function properly and deliver IV fluids at the correct rate without leakage, the seal required the right material formulation, exact sizing and molding to consistently tight tolerances (Photos 3 and 4).

Photos 3 and 4: The double lip seal is molded of a special EPDM formulation to very tight tolerances to prevent leakage. The seal fits precisely into the housing sleeve which is capped and bonded in place permanently.

Using Solid Works 3D modeling software, Mr. Mauhar and his MR&P team created a seal design concept with double lips that had extreme side-loading resistance.

Dr. Donawick in turn designed a protocol for testing these CAD designed parts allowing MR&P to verify its theoretical seal designs. Mr. Mauhar used finite element analysis (FEA) throughout the development stages both for the original double lip seal design and to revise the design when testing showed problems (Illustration 3).

Illustration 3: MR&P’s use of FEA facilitated improvements to the seal design through much iteration.

Material selection was critical. Drawing on its more than 50 years experience developing custom elastomers for difficult medical applications, the MR&P team settled on a specially formulated EPDM (Ethylene Propylene Diene Monomer) compound.

Formulated and molded to ensure low extractables, the seal material was compatible with the wide range of fluids that could be selected for administration through the IV system. Size of the seal also was important. Through various size iterations and testing, final dimensions arrived at were .346 OD, .140 ID and .145 (Inch) thickness.

Maintaining tolerances also was critical to product success. MR&P’s ensured repeatable quality with its state-of-the art molding operations resulting in tolerances on the following critical dimensional surfaces: ID +/- .004, OD sealing diameter dimension (.295) was held to +/-.005. Sealing thickness (.195) was held to +/.005 (Illustration Four).

Illustration 4: Seal cross section shows precise features maintained by MR&P’s molding processes.

Keeping the seal design as small as possible was cost saving and had functional benefits as well. The small seal allowed just the right capacity for correct fluid flow with no leakage. This small seal design also created less friction than a comparable larger design.(Excessive friction caused the coiled tubing to kink when the animal moved). MR&P designers improved the low friction feature by applying a medical grade silicone lubricant to the seal prior to assembly.

Precision Interlocking Components

The complete seal and bearing assembly is a combined effort of MR&P and Wycon Mold & Tool, Inc, Warminster, PA. The Flex-Coil® Swivel System consists of the following components:

  • Injection molded polycarbonate mounted housing with fluid chamber that holds the seal and bearing assembly.
  • Injection molded thermoplastic rotating hollow center pin that rotates in the seal.
  • Transfer molded EPDM formulated double lip seal.
  • Stainless steel washer.
  • Injection molded thermoplastic cap.

To assemble, the seal and washer slide onto the hollow center pin that is inserted into the housing sleeve. The cap, when bonded to the housing, creates a fluid reservoir chamber, holds the top of the center pin in alignment and prevents formation of side forces that could deform the seal and allow leaks. The cap locks the entire seal assembly into place.

The freely rotating pin is then ready to connect to the coiled IV tubing. Final steps include: testing to be certain the center pin turns freely; testing the swivel assembly for leaks with positive air pressure and a vacuum; spinning the pin for 30 seconds to evenly distribute the medical silicon lubricant. Needed medical tubing and connectors are attached to the coil; the completed sets are packaged and sterilized with Ethylene Oxide (EtO).

All design work for the Flex-Coil® seal system and a 73-cavity production mold were done at MR&P headquarters in Minneapolis, MN. Molding is performed at the company’s Watertown, SD manufacturing facilities, with annual quantities averaging 100,000 assemblies.

“The Flex-Coil® Swivel IV system with the new sealing assembly has been used successfully by veterinarians all over the world for nearly two years,” reports Dr. Donawick. “We really owe its success to the seal device Chris Mauhar and the MR&P team designed and continue to manufacture for us.”