Flex-Valve Technical Guidelines and References

Flex-Valve, is a brand under General Rubber Corp. representing our state of the art line of pinch valves, pressure isolation rings and duck bill check valves. It was founded with the purchase of the pinch valve division of Farris Valve, who held the patent on the original pinch valve. With the technical support of General Rubber, later acquisition of the Ray Wilcox Company and the addition of new and patented pinch and check valves, Flex-Valve has become a worldwide recognized brand and leading manufacturer in the industry.

Since our inception in 1950, General Rubber Corp has designed and developed a wide range of mechanical rubber products used in the most demanding applications. Rubber is one of the most compliant and resilient materials available. This not only makes it ideal for car tires, but also for pinch valves and duck-bill check valves as well. With a flexing cycle life in the tens of millions, fatigue is simply not a design concern. Improved performance and engineered solutions are often accomplished by incorporating advanced materials of construction and technologies to what otherwise would be considered a mature product line. This benefits both the specifying engineer designing an optimal system, as well as, the customer performing maintenance on, or upgrading an aging system.

The original pinch valve is at once simple and ingenious. Developed to handle corrosive and abrasive water in the flooded coal mines of Eastern Pennsylvania, the operators could restrict flow by using a pinching mechanism to bear down on a rubber sleeve. That simple idea now serves as the basis for more sophisticated products. The features and benefits of our pinch valves include abrasion and corrosion resistance, non-clogging, maintenance free and can seal drop tight even on solids. Catered to the demanding conditions of slurries and other difficult fluids, these products can out perform alternative products 10 to1. Many styles have common lengths with plug, gate and ball valves for interchangeability. The product is available with customized actuators, controls and sleeve types. The sleeve is the only part exposed to the process fluid and can eliminate the need for expensive body alloys.

The flow pattern of Flex-Valve’s pinch valves are inherently streamlined, making them well suited for modulating service, however sizing becomes critically important. For an on/off valve sizing is a simple case of maximum flow. If it is determined that a smaller valve can be used, the benefit is primarily economic. For a modulating valve, our control pinch valve, sizing is critically important for performance reasons and both maximum and minimum flows must be considered. The port must be sized to handle the maximum flow; however it is equally important to consider minimum flow so that it is not oversized. At minimum flow, an oversized port would need to operate near its fully closed position. This is a problematic position because the once round port is now completely flattened with a very shallow space remaining. This wide but very shallow space becomes a wear location as slurries have to pass through it. Another problem associated with this position is that small movements in the actuator results in large changes in flow. If the shallow space is only 1/4” for example, a 1/8” in actuator movement would have nearly a 50% affect on flow. This sensitivity is too tight and the actuator will constantly hunt for its ideal position. This constant hunting will cause terrible wear on both the actuator and the valve internals. Ideally we like to size the valve under 60% closed at minimum flow. In this position the initial round port only deforms slightly into an oval shape. Proper sizing results in better rangability and improved life of the actuator and valve internals.

Sizing the pinch valves is technically done using the ISA’s two formula method. The Cv (formula 1) is first calculated using the actual change in pressure across the system ∆Pact . If the allowable change in pressure across the system, ∆Pall (formula 2), is calculated to be less than ∆Pact , it must be substituted in the original Cv formula. Cavitation may occur if ∆Pact is greater than ∆Pall. Cavitation is a serious condition and while a funnel sleeve may be used to transfer its damaging effects past the valve, other system changes may be a more effective solution. To maximize sleeve life, the inlet velocity should also be held below 22Ft/Sec. or ideally below 14Ft/Sec. Our engineers are prepared to discuss the intricacies of the application, as well as size, and specify an optimal valve.

Flex-Valve’s duck bill check valves eliminate backflow and seals around entrapped solids. When used for storm water outfall/overflow systems they provide quiet, maintenance free operation with the added benefit of low opening pressure, thereby eliminating standing water, a major health concern. When used for submerged outfall diffuser systems they eliminate marine fouling and backflow intrusion with the added benefit of higher jet velocities even at low flow rates, providing a more uniform port discharge distribution. The versatile construction combined with our creative design team can adapt it to additional applications including water mixing systems, overflow vents, anti-siphon devices, coarse bubble diffusers, floor drains, sparging devices or even, when needed, to increase back-pressure in a pipeline.

Flex-Valve pinch valves, pressure isolation rings and duck bill check valves are catered to the demanding conditions of slurries and other difficult fluids. The experience and capability of General Rubber can effectively utilize these products in even the most demanding applications. In consideration of our products, you are assured that every aspect of your project will be our priority.

Thank you for your consideration.