Can you Teach an Old Tech New Tips?

Issue No. 35–December, 1990

We're asked all the time about the difference between old school and new school leak locating methods. People are curious to know which approach works better. We've found that in the last ten years or so there's been a shift from using pressure readings for leak locating to using air flow.

The main difference between the two strategies really amounts to what end of the cable you start working on first. If you're an old schooler, you'll be looking where the pressure's the lowest. And that means working toward the end of a cable--away from air sources. In today's air pipe systems, with their multiple air sources, emphasis is placed on looking for the biggest, highest flowing leaks. And in order to do that, you've got to start at the source. You need to identify flow rates, and then chase the leak that's flowing the most.

You can compare the air flow method of leak locating to putting out a fire with a garden hose. Let's say your house is on fire and you have to borrow your neighbor's hose. You turn it on and discover that it's full of leaks, some big, some small. It's the only hose you can use, so which leaks are you going to patch first? One of those tiny pinholes at the end of the hose? No way. You're going to fix the big ones that are keeping you from getting as much water on that fire as possible.

It's the same with pressure systems. You want to go after the highest flowing leaks. Air pressure alone will not indicate the worst leak in a system. In fact, it's entirely possible for a cable with 3 or 4 PSI to be in worse shape than a cable with 1 PSI. You need to know what the cable is flowing before you can determine if you are in search of a pinhole or a major tear in the sheath.

So, while yesterday's methods may have made the mark in the old school, they're not going to be much help in a system that requires quick reaction to system-threatening leaks. When you've got a high flow alarm, you have to go to the source and measure the flow. That way you'll be able to identify the size of the leak and where to look.