Redundant Anti-Siphon Capability: Combined use of Relief Valve & Vacuum Breaker
An engineering firm recently specified two seemingly unrelated valves to provide redundant siphon prevention in a ferric chloride piping system.

In many piping systems, when the pump is shut off, vacuum occurs as liquid drains from the highest point to the lowest point in the piping system. This downstream flow creates a vacuum, and as flow continues, it often creates a siphoning effect and drains the supply tank.

In many chemical applications, Plast-O-Matic Series RVDT Backpressure/Relief Valve is the leading valve for preventing siphon. It was the first state-approved thermoplastic valve for anti-siphon use in municipal water treatment systems, selected for its PTFE diaphragm and normally-closed design.

Redundant siphon prevention
Because of the critical nature of the application, system designers required a back-up to the RVDT – just in case. The valve selected? Series VBM vacuum breaker…and here’s why:

How it works
The RVDT uses a non-wetted spring to keep the valve closed. The set pressure (or opening pressure) is determined by pre-setting an adjusting bolt. When the pump is activated, and pressure builds above the set point, the RVDT opens and allows flow. The set point is based on the total feet of head in the tank plus a safety factor. When the pump is shut off, pressure drops below the set point. This causes the RVDT to automatically close bubble tight, and siphoning due to tank head pressure is prevented.

The most sensible plan was to use a normally-closed vacuum breaker that would positively seal bubble tight under even the lowest pressure, but open at minimal vacuum should the primary anti-siphon valve fail. Plast-O-Matic Series VBM, by virtue of its patented diaphragm, was the only product available to meet this requirement. Most vacuum breaker designs rely upon a floating ball for closure, but these are highly prone to distortion and leakage is common. Series VBM design is tested to over 1,000,000 cycles in laboratory conditions, and the diaphragm is easily replaced if necessary.

More information and specifications, Series RVDT/RVDTM please click here

More information and specifications, Series VBM/VBS please click here

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Plast-O-Matic Valves, Inc.
When it comes to thermoplastic valves and controls, we are the problem solvers.
Founded in 1967, Plast-O-Matic Valves' ongoing mission is to provide unparalleled customer satisfaction while continually advancing the technology of liquid pressure and flow control. As the quality leader in the development of thermoplastic valves and controls for corrosive and ultra-pure liquids, POM provides a complete line of standard and custom designed solutions for difficult applications. The company is committed to product innovation, engineering excellence, precision manufacturing, 100% quality testing, and hands-on technical assistance. ISO 9001:2015 Registered.

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