REDUNDANT ANTI-SIPHON CAPABILITY:
COMBINED USE OF RELIEF VALVE AND 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 corrosive 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.
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.
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:
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.
BONUS PUMP PROTECTION
In addition to siphon prevention, the series RVDT valve provides a number of additional benefits to the system. Most important of these is providing pump backpressure, as well as downstream (or diverted) relief in the event of overpressure. The backpressure function enables the pump to run more efficiently, as well as smoothing out turbulence.
Bypass relief enables some or all of the flow normally discharged from the pump to be bypassed or piped away to either the suction side of the pump or back to the feed vessel when an obstruction occurs in the piping system. In this case the valve is usually installed on a tee, or a three-way version is used.
When the obstruction is cleared and normal flow returns, the pressure in the line returns to normal and the valve closes. The key benefit is to prevent deadheading and costly rebuilds or replacements.
The valve is available in a variety of engineered thermoplastics, as well as stainless steel. For more information on these key piping system components and to safeguard your system, visit www.plastomatic.com.