Found a cheap trick for checking tire pressure on the ramp without a gauge

I used to walk back to the toolbox every time I thought a nose tire looked low. Last week I grabbed a broken ballpoint pen spring from the trash, cut it to about 2 inches, and shoved it in the valve stem cap. When I screw the cap on, the spring pushes the pin down just enough to let a tiny puff of air out if pressure is over a certain point. I tested it against a calibrated gauge on three different 737 nose tires and it matched within 2 PSI every time. It's not gonna replace the real tool for write-ups, but for a quick preflight check it saved me like 10 minutes of walking. Has anyone else rigged up a similar DIY tool on the line?

2 comments

2 Comments

jamies451mo ago

Hold on. Did you actually confirm the spring didn't back out or bind inside the cap at high vibration? I've seen those little springs break off and get lodged in the valve core. Then you're chasing a slow leak for three months. Also, how do you keep the seal from leaking around the spring itself? That little gap in the cap threads would bother me. I'd rather just carry a cheap stick gauge in my pocket. It's faster than screwing and unscrewing a modified cap.

flores.tessa1mo ago

Man honestly you make a real good point about the spring getting stuck in the valve core. I helped a buddy chase a mystery leak for weeks once and it ended up being a tiny piece of plastic from a shitty cap that snapped off inside. The seal around the spring thing is sketchy too cause even a little grit or dirt in those threads will let air creep out over time. A stick gauge is like $3 and takes two seconds, no chance of messing up your valve stem or dealing with a weird homemade part that might fail on a bumpy road.