The Cessna 120-140 Association Forum

Our 1947 120 has developed a pretty constant ( 1 drop every few seconds) leak on one of the wing fuel sumps. I could make out “CAV -170” so I’m going to order two from aircraft spruce. Just wondering about the process to replace these sumps, is it just a matter of draining the tank and then replacing?



https://www.aircraftspruce.com/catalog/ ... NnCRloG1X2

Did you try new o-rings? Much less expensive.

Yes, drain the tank, cut the safety wire, unscrew the valve. Installation is the reverse.

If........you haven't done this already........? I've replaced countless fuel sump drains on most GA aircraft at work. I have the other drain standing by(ready at hand), some rags, nitrile gloves on my hands and a bucket below.
I pull the offending (leaking sump) let the fuel drain for a second and quickly insert the replacement drain. I've never lost more than a pint of fuel.

Be certain that you're not scuffing your feet on anything in really dry air.........you don't want any static sparks, in other words, be aware of proper electrical bonding to the airframe when you perform this operation.

Another option is to have another drain (of questionable integrity) to plug the hole while you pull out your drain and either clean or replace the seal. Be aware! this is not an "O ring" but an actual seal (Like a flattened O ring) and Safe Air no longer sells them individually.............(that I'm aware of)

V529 wrote: ↑Thu Nov 27, 2025 7:33 pmBe aware! this is not an "O ring" but an actual seal (Like a flattened O ring) and Safe Air no longer sells them individually.............(that I'm aware of)

Are you sure? It thought the ones with square seals were the Curtis valves. I also thought the reason they stopped selling the seals was because there was a rash of failures when the little washer that was peened onto the end to hold the seal came unpeened and the valve core was ejected.

https://www.saf-air.com/products/fuel-valves.html

Saf-Air valves are simple 0-rings according to their website
O-RINGS: All valves M83248/1 Size -006 CAV-170 Size -012, CAV-180 Size -011

The Curtiss valves have the weird o-ring and they are not rebuildable

Hmmmmmm,

Yes.............I guess I should have differentiated between the two. I still have some Curtis seals.........the ones with the squished O rings. Sorry for the confusion!