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A leading U.K. manufacturer of 1000 litre IBC's was experiencing problems with a spring-operated vacuum breaker. The spring design did not provide an effective seal and permitted fugitive emissions. The problem was most significant during transport, when sudden motion resulted in severe product leakage. Because the IBC manufacturer's largest customer was primarily shipping a solution of 36% hydrochloric acid, the situation was critical.

The company tested a number of vacuum breakers, but was unsatisfied until finding a U.S. manufactured product from Plast-O-Matic Valves, Inc., based in Cedar Grove, New Jersey. The Plast-O-Matic "True-Blue" Vacuum Breaker, with a one-of-a-kind elastomeric diaphragm, was the only corrosion-resistant device able to meet the design criteria: Prevent tank implosion, yet remain sealed in all other situations regardless of motion or mounting position.

Patented Diaphragm

The diaphragm in the Plast-O-Matic vacuum breaker creates a bubble-tight seal, and sealing is unaffected by motion or direction. Installation at the highest location in a tank is recommended. After breaking a vacuum, the patented design causes the diaphragm to reposition and close in an identical location - a quality known as "positive repetitive sealing" - which means that it will prevent emissions and leaks throughout the life of the IBC.

To maintain the bubble-tight seal, the "True-Blue" Vacuum Breaker requires a minimum vacuum of at least 2" Mercury (1 PSI) to open, which is well within the maximum negative pressure of 10" of Mercury for an IBC. The flow rate of the vacuum breaker at 10" of Mercury is 50 cubic feet of air per minute. For tanks that can withstand 20" of Mercury, the flow rate is 95 cubic feet of air per minute. The breakers are manufactured in PVC, Polypropylene, Kynar® (PVDF) or PTFE® (PTFE) and fulfill the need for corrosion resistance in chemical IBCs.

After reviewing case histories of the Plast-O-Matic vacuum breaker in other tank applications, the IBC manufacturer tested and soon specified it into the product line. Since the switch, the emissions and leaks have been eliminated.

Useful in Many Tank Applications

Plast-O-Matic's vacuum breakers are designed to protect many different types of tanks and storage vessels from collapse or structural damage during draining or pumping, as well as to prevent liquids from siphoning back into a tank. In one popular tank design, the breaker prevents liner separation It is also used in large underground storage systems, where the "True-Blue" Vacuum Breaker is installed in an above-ground housing and connected to the tank or cavity via piping. The breaker is surprisingly compact, in pipe sizes from 1/2" to 1" npt with total height ranging from 4.3" to 5.1". Maximum working pressure is 6,9 bar @ 24ºC (100 PSI @ 75ºF).

A special cap protects the Plast-O-Matic vacuum breaker, by preventing foreign matter from entering the valve. It is also designed to minimize the "whistling" commonly associated with these devices. But for tank manufacturers and system designers - who know that vacuum conditions can wreak havoc - a little whistling is music to the ear!

In addition to vacuum breakers, typical Plast-O-Matic products associated with tanks and storage systems include check valves, relief valves, by-pass valves, gauge guards, level indicators and sight glasses.

The Sight Glasses are installed on 1/2" connections at key points in the bottom of the outer containment pipe. In the event of a leak, the fuel will collect at the lowest point--the sight glass--and raise a day-glo float in the chamber. As the brightly colored float rises above a blackened portion of the sight glass, it creates instantly recognizable visual confirmation of the problem.

Constructed of corrosion-resistant Pyrex® on the inside wall and high-impact acrylic on the outside, the Plast-O-Matic sight glass meets the need for for dual containment throughout the system. O-rings allow the indicators to seal at low pressure as well as high pressure, an attractive feature for dual containment systems. A full 360° viewing area in the sight glass permits inspection from anywhere near the piping.

Useful in Many Applications

Plast-O-Matic's sight glasses are designed to give instantaneous visual confirmation of pipeline flow. In another application, the sight glass is installed directly in a soil remediation system, where streamers within the chamber flutter when flow is present. It is also frequently used to visually confirm the presence of a process additive; in these cases the sight glass is installed downstream of an injection system. The sight glass is surprisingly rugged, and is available in pipe sizes from 1/2" to 8" npt. Standard O-ring seals are of Vitonr or Buna-N.

The sight glasses, from Plast-O-Matic's"True-Blue" line, are manufactured with PVC, Corzan® CPVC, Polypropylene, Kynar® PVDF or PTFE® PTFE ends.

This chart is only a general guideline, based on laboratory conditions. In real applications, systems vibrate, UV rays affect performace, temperature fluctuates....these and a myriad of other everyday conditions will adversely affect plastic piping.

As temperatures rise, the plastic softens. As temperatures decrease, plastic becomes brittle. Ultravilot rays (sunlight) slowly degrades the molecular structure of most plastics. Vibrations create inherent stresses, which can lead to cracking.

The degree of oxidation is dependent on the level and intensity of exposure: In sunlight, oxidation can take a number of years and will result in discoloration and embrittlement. This does not affect performance or pressure capacity - so you may not have a problem - but it does make the valve vulnerable to impact damage.

When a PVC or polypropylene valve is connected to a UV sterilizer the level of exposure is much greater, and the thermoplastic is eventually prone to stress cracking. For UV sterilizers, PVDF is generally the valve material of choice and is not subject to the same type of degradation.

In outdoor applications, heavily pigmented common latex paint will inhibit the damage from sunlight. In some situations, however, painting may not be practical. In polypropylene applications, paint does not properly adhere to the thermoplastic. PVDF may not be cost-effective or desired in certain applications as well.

Plast-0-Matic now offers UV-Resistant thermoplastics as an optional valve material for applications exposed to UV where paint or PVDF is not practical. Manufactured from Grade 1, Type 1 PVC or polypropylene with added carbon black, these valves generally withstand UV exposure with less oxidation and molecular degradation.

The added carbon black effectively blocks the UV component, and allows the valve to maintain its properties even in installations with high UV exposure.

UV-resistant PVC or polypropylene eliminates the need for paint and other costly maintenance techniques, yet costs only slightly more than standard resins.

The UV-Resistant feature is available on most popular Plast-O-Matic valves up to 2" pipe sizes. Minimum quantities apply and these materials may not be practical in every situation with UV exposure. To determine the best solution for your specific application, contact our Technical Sales Team in Cedar Grove at 973-256-3000.

Dealing with pH levels below neutral, the Engineering Division of Bremerton Public Works and Utilities had to provide a system for injecting caustic soda into the water main. "We deal with a number of different sources," explains Tom Knuckey, head engineer, "a few surface water sources, supplemented by some wells, so the pH varies."

To compensate for the fluctuation, a pair of 4,000 gallon tanks with a series of metering pumps and analyzers allow the caustic soda to be diluted when the water supply is closer to neutral. "It may start at full strength, then go to 50% strength, 25%...whatever is needed," explains Knuckey.

The system design called for precise dosing into the pipeline from a pair of valves controlled by pH sensors upstream and downstream of the treatment point. The 30 PSI backpressure created by the city water main was a primary concern. The valves specified would have to open and close accurately against the high backpressure, and resist corrosion from the sodium hydroxide.

Overcoming the corrosion problem was relatively simple; thermoplastics would provide significantly better performance than metals. Of the common plastic valve materials, polyvinylchloride (PVC) was selected for its compatibility and relatively low cost. At that point, the possibilities covered a wide range of valve styles and actuation package combinations.

For speed and dosing accuracy, solenoid valves were the most likely candidates. The main pipeline, however, posed a problem since most standard 1" pipe size PVC solenoid valves cannot actuate against 30 psi backpressure a deliver a high flow rate.

While searching for a solution, Bremerton Public Works contacted Plast-O-Matic Valves, Inc. of Cedar Grove, New Jersey. Plast-O-Matic, one of the longest established plastic valve manufacturers, suggested a solenoid valve with a "pilot" orifice. Known commonly as a "pilot-operated" solenoid valve, it uses a standard sized coil to first open and close against a small amount of flow. The line pressure, in turn, is used to actuate a much larger main orifice. The pilot design is slightly slower than a direct-acting solenoid valve, but is able to provide excellent flow capacity with relatively high pressure. The split-second hesitation inherent to the pilot provides the added benefit of virtually eliminating the water hammer that an instantaneous solenoid valve might cause.

The valve specified, Series PS from Plast-O-Matic, offers flow capacity from 5.2 Cv to 80 Cv depending on size. The design provides an inlet pressure rating to 140 psi and backpressure to 70 psi. A pressure differential of 5 psi is required for the valve to operate properly. In the Bremerton installation, a 1" valve was specified, which provides a Cv of 9.5. The Series PS also offers a number of appealling safety features to the public works team: It provides a patented "Fail-Dry" safety vent, which allows the valve to continue operation in the event of a primary seal failure. The PS also has a PTFE bellows dynamic seal, offering the ultimate protection against fugitive emissions.

To further enhance the accuracy of the system, Knuckey's crew also specified a corrosion-resistant back pressure/relief valve from Plast-O-Matic. Known as the Series RVDT, these valves provide a constant backpressure on the discharge of the caustic soda metering pumps. This allows for a repeatable, constant fluid discharge per stroke, and enhances the system accuracy.

According to Bill Davis, P.E., who worked with Plast-O-Matic to specify the valves, Bremerton Public Works has initiated start-up of the new water system. The pH treatment facilities are slated to be fully online during second quarter 1999. Once it is fully operational, the water system is designed to provide six million gallons per day.

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