Gas regulator vents kept ice free with splash-guard.
One step in the safe handling and use of natural gas for the home involves proper venting for gas regulators. Most residential natural gas regulators employ a standard internal relief valve, allowing regulators to vent to atmosphere in an over-pressure situation.
Without a properly operating vent, pressure can rise to levels that can cause problems for downstream appliances. For example, over-pressurization can result in a stove or hot water tank getting a large flame, which may cause the pilot to go out and allow dangerous fumes to leak into the enclosed atmosphere of the home. It could even result in an explosion or fire.
If downstream pressure starts to rise appreciably above the set point, regulators are designed to relieve that pressure by venting gas safely to the atmosphere. Problems can occur, however, if something prevents the vent from "breathing" freely. In such an instance, it can't relieve the initial pressure surge and the pressure continues to build up in the system.
"The primary function of a natural gas regulator is to control pressure, to relieve that pressure if it gets too high. Residential regulators maintain a constant pressure and help ensure the safe delivery of the natural gas," said Ontario-based Bruce Barnett, vice president of Elster Meter Services Group.
Ensuring that vents are unobstructed and functioning properly so they can provide relief in the event of over-pressurization is important. However, while utilities and suppliers make every reasonable effort to ensure safe delivery of natural gas, sometimes customers and weather conditions combine to undermine even the best safety measures, as may occur when icy conditions impair the vent's ability to relieve.
Many homeowners inadvertently create dangerous conditions by trying to shield pipes and hardware from view with decorations and plants or by carelessly leaving toys, tools, and other objects lying near the vent. As a result, they can end up contributing to conditions that prevent the proper operation of the regulator vent. With all these extra surfaces near the vent opening, water can easily splash into the vent and collect on the screen. While this is not a problem in warmer temperatures, when the seasons change and cold temperatures become the norm, the threat becomes real and the problem is magnified.
"In winter, a particularly hazardous situation occurs when we get snow and ice. In cold weather, regulator vents can freeze shut, preventing the regulator's diaphragm chamber from breathing. This can be a common problem in areas that experience melting snow or freezing rain, such as Canada and the northern parts of the United States," said Barnett.
As a culprit, ice is particularly difficult to catch in the act and so it is hard to quantify exactly how often it is the cause of blocked vents. There are many unexplained regulator failures and safety incidents. These incidents may well be due to freeze-off of the vent. However, in the natural course of events, the evidence of the freeze-off simply disappears.
Many in the utility market believe that frozen regulators are a large problem. However, the evidence of the freeze-off is often gone at the time of inspection. In the worst case, a fire melts the ice or, due to freezing conditions, the firefighting measures result in the meter set becoming entirely encased in ice, eliminating the detection of a frozen vent.
Devices such as covers and hoods have been put on vents for years to protect them from ice buildup. Yet, even with protective covers, there were instances when vent regulators were frozen over by ice. At first, industry experts considered freezing rain to be the source, thinking that perhaps water would rain directly into the vent and freeze on the screen's surface. However, in a proper installation, this doesn't happen because the vent faces down.
Basically, there are two configurations: outboard and inboard. In the outboard configuration, the vent points downward at a 9 o'clock position when facing the meter set and away from the meter. With an inboard configuration, the vent is at a 3 o'clock position. In that arrangement, it points down over the top of the meter. The right set of circumstances can allow water to drip onto the meter, splash up into the vent, and freeze to the stainless steel screen.
However, in a properly installed, downward-facing regulator vent, even freezing rain won't block off the vent. It takes another set of circumstances to create the problem. Enter the homeowner's decorations and toys. By shielding pipes, meters, and hardware from view or by leaving toys and yard furnishings around regulators, homeowners introduce surfaces that can cause water to splash up into the vent.
The problem is not with ice, snow, and water entering directly into the vent, but rather with this splash effect. In a normal freeze-thaw cycle, water from snow and ice melting during the warmer, daytime hours drips from an overhang or roof and splashes onto things that surround the regulator. As the relatively warm (just above freezing) water hits the bricks, plants or, in the case of an in-board configuration, the meter itself, it splashes up and into the vent and adheres to the screen. Then, as the sun sets and temperatures drop, the water can freeze, blocking the vent and allowing a potential dangerous level of pressure to occur.
"An even more common scenario is that, during a day in which the temperature is only a few degrees below freezing, the roof faces the sun," Barnett said. "While the actual temperature may still be below freezing, the direct sunshine causes the snow to melt. As it drips off the roof at a temperature slightly above freezing, it contacts a splash surface and splashes back up into the vent. Because the actual meter set temperature and vent screen surface is below freezing, once the drip is out of the sun and hits the screen it freezes quickly.
"As this action continues, a layer of ice builds up on the screen and can eventually block the vent," Barnett continued. "The same scenario can occur if a heated building has snow on a roof that does not have good insulation. As a result, the roof snow melts even without the sun and runs off on a freezing day or night."
Extensive testing by the metering industry and standards organizations identified the "splash-back effect" as the primary source of vent freezing. However, a simple solution to blocked vents has emerged in the form of a splash guard, a risk abatement device that protects vent surfaces during these colder times.
With no moving parts, the splash guard prevents water from splashing into the vent and reaching the screen. Either retrofitted in the field or installed as an enhancement in the factory, the device, marketed as Splash Guard[R], is in use in Canada and the United States. The device is approved by the Canadian Gas Association, a leading developer of standards and codes. It protects the vent screen from splash back and provides a large venting area to keep regulators working effectively and vents breathing easy.
It is comprised of three components: a covering cone, a baffle plate (splash plate), and a stainless steel screen that is identical to the standard screen in a regulator vent. The device works by using a shield plate to prevent water from reaching the vent screen.
Splash Guard fits the 3/4-inch or 1-inch vent of any residential unit. It expands the venting area to the 3-inch diameter of the cone, giving it more breathing room and greater protection.
Other than the stainless steel screen, the guard is made of durable, impact-resistant, high-density polyethylene (HDPE). As such, it is well-suited for all outdoor conditions and temperatures.
Quick and easy installation in the field is accomplished by removing the existing screen from the regulator and threading the Splash Guard into the regulator vent.
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|Title Annotation:||Tech Notes: Product Development|
|Comment:||Gas regulator vents kept ice free with splash-guard.(Tech Notes: Product Development)|
|Publication:||Pipeline & Gas Journal|
|Date:||Jul 1, 2008|
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