Hello To All,
I want to comment on a statement in a recent posting:
“ The other piece of equipment I now use is a simple back flow valve. Some counties require them. They address the issue of back burning, a phenomenon of the flame front being sucked down a line if the gas / oxy is shut down at the tank while the torch is still burning, rare, but I’ve seen it.”
It is important to understand the distinction between backflow check valves and combination flashback arrestor check valves. Backflow check valves are designed to prevent a high pressure gas from flowing down a lower pressure pipe or hose. For example if a jeweler’s torch tip is blocked the higher pressure of the oxygen supply will overcome the lower pressure of the fuel gas and oxygen will flow into the fuel line and a backflow check valve will stop this.
However, if the tip is blocked and there is a flame in the torch then not only will oxygen flow the wrong way but so will a 5,000+ degree flame which will burn back to the fuel source, then explode.
The difference between a backflow check valve and a combination flashback arrestor check valve is that when the flame meets the backflow check valve it will melt the check valve and keep going to the fuel gas source, whether a cylinder or the utility gas meter. When the flame meets a combination flashback arrestor check valve the flame will be extinguished AND the flow of oxygen into the fuel line will be stopped.
Some jewelers believe they are protected by installing a simple check valve on their fuel and oxygen supply hoses or pipes…they are not. Only a combination flashback arrestor check valve puts out the fire.
Several years ago NYC Diamond District jewelers were literally exploding their utility gas meters because they were using city natural gas at less than 1/4 psi with oxygen at pressures between 5 – 70 psi and causing flashbacks. The NYC Fire Department and natural gas utility, Con Edison, did extensive research and testing to determine the cause and solution. They found that jewelers were not using flashback arrestors because the utility gas pressure was so low that the flashback arrestor blocked gas flow; jewelers could not light their torches. They also found that simple back flow check valves were insufficient to stop a flashback event.
The NYC Fire Code was revised to require jewelers using utility natural gas (“piped gas”) to have a pressure booster device capable of boosting natural gas to at least 5 psi and installing UL Listed combination flashback arrestor check valves on jewelers’ torches. G-TEC Torch Boosters were approved by the Department of Buildings and Fire Department for this application and are now required for all jewelers connecting their torches to the utility gas supply. More information about what the Fire Code requires for NYC jewelers is here: http://www.safe-t-gas.com/NYCJewelers.html
Whatever the fuel supply jewelers should have a UL Listed combination flashback arrestor check valve on both the fuel gas and oxygen hoses or pipes; a back flow check valve will not protect you from a torch flashback.
G-TEC Natural Gas Systems