The zip tie trick that saved me 2 hours on a 737 bleed air leak

I was chasing a bleed air leak on a 737 at the gate in Phoenix last Friday. After my third round of clamping and spraying soapy water with zero luck, I tried that old trick where you wrap a piece of string around the suspect fitting and pull it tight. Found the leak in under 10 minutes where the fitting was just barely loose. Has anyone else used the string method for finding tiny leaks that won't bubble up?

3 comments

3 Comments

jessica_hall492mo ago

Wait have you guys tried this with a stethoscope? I keep a cheap mechanics stethoscope in my bag and it works even better than the string trick. You put the probe right on the fitting and you can hear the hiss through the earpieces before it even makes a bubble. The string method is great but the stethoscope catches those super tiny ones that barely make a sound. I found a pinhole leak on a 757 pack valve that way once when the soapy water was freezing too fast to see bubbles.

nguyen.tara2mo ago

the old trick where you wrap a piece of string around the suspect fitting" yeah I heard about that from my buddy who works at an oil change place. He was chasing a vacuum leak on some old rusty truck and spent two hours with soapy water getting nowhere. A senior mechanic walked over, grabbed a piece of twine from the trash, wrapped it tight around a hose fitting, and told him to pull it like a shoelace. My buddy said the string started vibrating and whistling almost right away where the leak was. He felt like an idiot but that guy saved him the whole afternoon. Now he keeps a ball of string in his toolbox for exactly this kind of thing.

king.wyatt2mo ago

On a widebody cargo plane out of Memphis last winter, I had a similar issue with a pneumatic line that wouldn't bubble no matter how much soap I put on it. I grabbed a zip tie, cinched it down tight around the suspect coupling, and listened for a hiss. The noise changed right where the tie was biting into the rubber and I found a tiny crack on the fitting's shoulder that was barely visible. After that I started keeping both string and zip ties in my pouch for the same reason. It's one of those cheap tricks that makes you wonder why you didn't think of it sooner.