Case History Feature
Case History Feature written for Igus, Inc. by Richard Stewart
ECONOMY VALVE DESIGN
TURNS ON PLASTIC BEARINGSSticky Problem Solved by Maintenance-Free Iglide™ Bushing
Irrigation and water issues are front page news in California's fertile
Central Valley, home of Waterman Industries, Inc., a $35 million
manufacturer of water control devices for agriculture and industry.
The company recently introduced an economy line of butterfly-type
valves, used extensively in agricultural irrigation, to compete against
products from offshore manufacturers. But early problems with a
bushing almost caused the company to scrap the program. A plastic
bearing from igus, inc. in East Providence, R.I., provided a cost-
effective solution that saved the now-successful product line.Known for the high-quality and durability of its products, Waterman
has been designing and manufacturing valves, gates and other
components for irrigation and wastewater treatment systems since
1912. Feeling competitive pressure from offshore producers of less-
expensive, light-weight valves, the company decided to develop a
lower-cost alternative to its line of heavy-duty butterfly valves.Plastic Reduces Costs
One way to reduce the costs of producing the new valve was to use
plastic rather than brass or bronze for the bearing that supports the
stainless steel shaft within the valve's cast-iron housing. But
Waterman was determined not to compromise its quality standards
just to produce a low-cost product, according to Don Appling, CEO
and president. And the quality he demanded was missing from the
early prototypes."We were having problems with the bushings we were using. A local
injection molder was making them for us from reinforced nylon,"
recalls Appling, who represents the third generation of the family-run
firm. "We went to igus and got a much more precision product —
and saved money."
Jim Pyles, Waterman manufacturing engineer responsible for
developing the economy line of valves, designated the Waterman
VBE2 Butterfly Valve, explains that the bearings used in the prototypes
could not maintain the dimensional control stability that was required.
"There was too much variation in the molded product," he notes. "But
in the igus bearings, we don't see that variation. It has a better finish
and performs much better."Plastic Over Metal
Pyles didn't need to use metal bearings in the VBE2. "The only
advantage I could see in metal is that it will take a higher unit pressure,
and we didn't need that for agricultural valves," he explains. "Brass or
bronze is more expensive, plus there's more of a corrosion factor with
metal than with plastic." Corrosion and chemical-resistance are
important factors in agricultural water, which can be acid or alkaline.In addition, particles of grit and silica can embed more easily in the
plastic material than in metal, providing better wear. "Performance-wise,
the igus bearings provide a very good coefficient of friction with water,"
notes Pyles."The major advantage we get from the igus bearings is in dimensional
reliability. The igus bearings have allowed us to close up our tolerances
in several areas and make a better product," he adds. "We've extensively
pressure-tested and cycle-tested the valves to the point where we broke
the cast-iron housing without appreciable damage to the bearing," he
adds. "We expect the bearing to outlast the rest of the valve."Valves for Irrigation
Designed for agricultural use, the Waterman VBE2 valve typically joins
two pieces of irrigation pipe to control the flow of water through the line.
Inside the valve housing, a rotating disc is fitted to a stem, which actuates
or opens and closes the valve by means of an operator — a manual lever,
wheel or an automated type.Waterman uses a variety of different size bearings from igus, which
pioneered the development and application of engineering plastic
technology to bearings over two decades ago. igus designs and manufactures
iglide™ bearings from engineered plastic compounds, tailored to meet the
requirements of a broad range of uses. For Waterman's butterfly valve
application, bearings made of iglide G300 material were selected.The material consists of a wear-resistant thermoplastic alloy base, a network
of long composite fibers, and a mix of solid lubricant, which homogeneously
impregnates the material. The fibers provide high strength (21,750 psi tensile
strength) and resistance to compression (compressive strength of up to
11,600 psi). The solid lubricant provides excellent anti-friction and low-wear
properties, without the need for a separate lubricating film or coating like metal
bearings. The G300 bearings are totally resistant to alkali solvents and to most
moderately strong organic and inorganic acid solutions. The material also
offers excellent abrasion resistance.Broad Range of Sizes
Igus manufactures and stocks plastic bearings in a broad range of sizes and
grades for prototype, pre-production and production use. Waterman needed
several bearings in lengths longer than igus offered as standard, Pyles remembers.
"But they agreed to produce the tooling and molds to supply us with the lengths
we needed," he says. Designers are encouraged to contact igus if the standard
iglide product range does not meet their requirements."We can check their specifications for technical feasibility," says igus
spokesman Carsten Blase, who notes that the company routinely develops
new products in response to customer inquiries. A comprehensive catalog
details the complete iglide product line and includes a questionnaire designed
to help specify the right bearing material for a specific application. The
completed form can be faxed to igus for a computer analysis and product
recommendation.Iglide bearings are designed to be press fit into the housing, without special
tools or lubricants. The self-lubricating property of the bearings provides a
distinct advantage over metal bearings, which are typically pressure-lubricated
through a hole in the journal that houses the bearing. Oil and other lubricants
can become contaminated with dust and solid contaminants, reducing the
bearing's performance and its life. The oil-free iglide bearings require no
additional lubrication and are totally maintenance-free, which further reduces
the cost of operation.Valve Construction
Waterman's VBE2 valves are offered in five sizes to fit pipes of 4" to 12" in
diameter, for applications with a maximum operating pressure of 150 psi. The
product incorporates a stainless steel stem, cast-iron body and disc, and a
replaceable, one-piece rubber O-ring that seals the disc and stem. A manual
lever operator is standard; other types are available — from geared or
traveling nut operators, for increased torque loads, to fully automated
electrical, pneumatic, and hydraulic operators.Waterman Industries operates around the world, supplying water-control
contract services as well as components for agricultural irrigation, sewage
treatment systems, and industrial applications. Company headquarters and
the main production facilities are in Exeter, Calif., halfway between Fresno
and Bakersfield. Other plants are located in Texas and Tennessee.Sales of the economy butterfly valve have been increasing steadily since its
introduction, Pyles reports. "Our valve is a lot beefier than the offshore
competition," he says. "It's more expensive than theirs, but it's also going to
last a good deal longer. Compared to the imports, we're making a higher
quality valve. And that's our niche."Value of Components
"We came close to scrapping the whole line, but thanks to the igus bearings,
we successfully resurrected it, and it's going to be a real good product for
us," adds Pyles. "I had made a pretty good study of bushings, and I settled
on igus for availability, cost, and performance," he notes. "I'd say that igus
definitely had a place in the success of the design."For more information on igus iglide products...
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