Case History Feature
Case history feature written for GLS Corp. by Richard Stewart
Medical Syringe Performance
Improved by New-design Seal
Molded of Thermoplastic Dynaflex,
Three-Ringed Seal Eliminates Liquid Blow-by
Medical syringes, like other equipment used in the care
and treatment of patients, have to meet high performance
standards. One example of a product engineered to exceed
those accepted standards, yet maintain its cost-effectiveness,
is a piston syringe from Welcon, Inc., a Providence, R.I.,
manufacturer of disposable bulb and piston syringes for
feeding and irrigation procedures.
The molded-plastic syringe features a seal on the end of
its plunger that combines elements of two standard seal types
an o-ring and a grommet. The result is a grommet with three
rings molded into its side. The rings fit snugly against the
barrel of the syringe, providing an excellent seal. It's molded
from Dynaflex, a thermoplastic elastomer from GLS Corp.
of Cary, Ill.
The ringed grommet replaced an o-ring seal in Welcon's
line of piston syringes. The design's success was dependent
to a large extent on the thermoplastic elastomer compound
from which the component is produced. The material had
to be processable with the company's injection molding
equipment. And it needed to be soft and pliable enough to
insert into the syringe barrel, yet sturdy enough to provide
the seal desired by Welcon.
GLS, a national distributor of thermoplastic elastomers
and thermoplastics, offered its technical resources to help
Welcon come up with solutions to its engineering and
production problems. Welcon had spent several months
experimenting with other materials before contacting GLS.
Welcon Quality Assurance Director George Hird credits
GLS for the support and technical assistance it provided.
"Before we went to GLS, we tried a number of other
materials and mold designs," he says, "but didn't find
anything that would give us the improved performance
He explains that the grommeting material had to be of
high quality, yet economical, and able to be molded at a
certain level of cycles. "We told GLS what we wanted to
accomplish, and eventually got what we needed. We wanted
a product that was better than our competition could
deliver and we have it, thanks to Dynaflex."
The Dynaflex compound is a custom formulation
designed to meet the unique tooling and sealing needs of
Welcon, according to Paul Weyna, GLS marketing manager.
"It had to be sterilizable and of uniform color," he notes.
"GLS has a lot of experience with these compounds, and we
felt certain we could deliver what they needed for that
Samples sent by GLS were processed and tested for
suitability by Welcon's engineers, who consulted with GLS
technical staff members, comparing test results, until a
material with the performance qualities the company needed
"We were able to reduce the shrinkage of the compound,
so the finished part had a larger surface area than other
materials they tried," Weyna explains, "without making any
adjustments to their tooling. We fine-tuned the compound so
it suited their needs better than any of the other materials."
He feels the partnership forged by the two companies is a
strong one. "Welcon is a very good customer to work with.
They were able to explain exactly what they needed for their
molding operation and how it would be used in the finished
product. And we began immediately to work on a solution
Welcon was looking for a competitive edge in this highly
contested segment of the medical marketplace. The company
manufactures three varieties of cost-effective syringes. The
line includes 14 enteral feeding-related devices and 17
irrigation products. The irrigation syringes and system
components are used for cleaning and placing enteral feeding
tubes, cleansing urinary catheters, flushing ostomy devices
and caring for decubitus ulcers, among other procedures.
The design of the Welcon piston syringe eliminates a
problem called blow-by that occurs in syringes. Blow-by
typically is seen during aspiration when liquid is being
pushed through the barrel of the syringe and a restriction
is encountered. The plunger seal can fail under the pressure,
allowing liquid to escape back into the barrel and leak out.
Generally, the condition is due to a defective rubber o-ring
or sealing grommet.
William Zangi, Welcon's VP Manufacturing, sought to
improve on the butyl rubber o-ring seal the company was
using in its piston syringes. Combining both the ring and
grommet types, he designed a grommet that provides a
better seal than either type alone one that eliminates
He notes that while an o-ring can provide a good seal
at a low cost, it is not the most dependable. The ring has
a limited surface area, and the slightest deviation or defect
can result in failure of the seal. The multi-ringed grommet
designed by Zangi improves on the o-ring concept,
increasing the surface area of the seal.
Hird, who is responsible for approving suppliers and
ordering raw materials, as well as with the quality of the
finished products that leave the plant, was very impressed
with the support from GLS. "We've found that we can
rely on them. They have a very good rating with us," he
reports, noting that his Quality Assurance Program sets
criteria for suppliers to meet in order to qualify as vendors.
"Like us, GLS has a quality assurance program, and
they are customer-driven," notes Hird, who has been in
charge of Welcon's quality program for 16 years. "GLS
understands the regulations that we have to comply with,
and they can meet our delivery requirements so we
don't have keep a high inventory of material on hand."
Welcon receives the Dynaflex material boxed in pre-
colored pellet form on a just-in-time delivery basis.
"We are proud of the quality of our relationships both
with our customers and our vendors. And we are proud
of the quality of our products," Hird adds. "Our multi-
ringed grommet design has given us a better product than
we had with the o-ring type seal thanks, in large part,
to our partnering with GLS.
"This syringe is a significant improvement to our line,
we feel, because the end-users, the people who are
tending their patients, now have a product that's more
dependable. If we can make their job a little easier, then
our efforts have been worthwhile."