Sump drain leaking PA-28

[Rebel Lord]

The sump valve is leaking on the Cherokee pretty bad. Is this something I as pilot can unthread and replace or do I need a mechanic?

 

[Lndwarrior]

The following is based on the "sump drain" being in the wings and not the gascolator sump.

Easy to unthread. If you have gas in the tank you have to options. Drain the tank or, if you have a spare valve, you can quickly unscrew the leaking one and install the replacement. The first time you might spill a little gas but with practice you can do it will little gas spilled.

It's either some small piece of detritus stuck in the valve which is easy to clear, or the tiny o-ring is worn out/broken. These parts are cheap so its good to buy a spare valve and a few spare 0-rings and keep them in the plane.

Don't know if this is technically legal for you to do on a certificated plane, but it so simple it should be.

Gascolator sump can be a little more tricky, depending on the plane.

 

[Hang 4]

Do you have a GATTS jar? If so, try opening the sump all the way and letting a good stream get going. Then close it by letting it spring back. That can often dislodge a bit of crud that might be the cause of the leak. Do that three or four times for good measure. Replacing still might be the best option, but this is a good temporary measure.

 

[Domenick]

As above, assuming tank valve, not gascolator.

Have the new drain valve, a brass plug, and wrench in reach.
Crack loose the leaking drain valve.
By hand, press up as you unscrew. When loose, in one smooth motion, slide the drain aside and slide weak hand thumb over hole.
In one smooth, fluid motion, slide thumb aside and start new drain valve.
Tighten by hand.
You'll loose a few tablespoons of fuel.
DO NOT OVER-TORQUE. Cracking that collar brings a world of hurt. 40-45 INCH-lbs. MAX.

Wear gloves if you want. Some folks wrap a towel around their wrist.
If you get into trouble, use the plug or old valve.

Replace seal in the old valve and save for next leak.

 

[Bell206]

Is this something I as pilot can unthread and replace or do I need a mechanic?

Depends on how you look at it. If you apply the definition of preventative maintenance found in Part 1, to the list of prevent mx tasks in Part 43 Appdx A(c), you'll find your sump replacement is similar to other tasks listed.

Given there is existing guidance that supports this expansion of prevent tasks like the Coleal LOI, my personal take is you could perform the sump replacement provided you made the appropriate record entry per 43.9 and used the proper references and parts.

The one person who may have an issue could be the IA that performs your annual. Maybe check with him? Regardless this was how I worked with my owner-assisted customers when it came to prevent mx tasks.

However, as mentioned above, may want to see if you can first clear and reseal the sump by purging. Just think ahead and be prepared in case the valve goes south and sticks open with usually a full tank of gas.

 

[Dan Thomas]

DO NOT OVER-TORQUE. Cracking that collar brings a world of hurt. 40-45 INCH-lbs. MAX.

Yes. Most folks don't know how little torque is required on pipe fittings. The torque chart from the Lycoming overhaul manual is instructive:

40 inch-pounds max on a 1/8"NPT thread. That thread is tapered and will spread the boss and crack it easily. The boss on the MS carburetor bowl drain port is easily split like this.

1/8" NPT is about 3/8" diameter on the outside of the thread. 1/4"NPT is about a half-inch. Pipe thread sizes are given in nominal INTERNAL pipe diameters, not the outside diameter.

Some drain valves are a 7/16" straight thread. They're not self-locking like the tapered pipe, so lockwiring is usually used. They have an O-ring just under the hex head to seal the valve to the tank.

Best to use a bit of EZ-Turn (formerly Fuel Lube) on the pipe threads. Don't use teflon tape. Bits of it can end up going where it shouldn't, including that drain valve and fouling it, making it leak again.

Do this outside, not in the hangar. The fire risk is big. 100LL on your skin isn't good, either.

 

[Capt. Geoffrey Thorpe]

Take a rubber hose (say 1/4 inch ID), put it up against the sump drain, push the drain open while you blow into the other end. If the problem is a bit of junk under the O-ring, it may blow clear. Of course, there is no guarantee that the same bit of junk won't get stuck again at a later date and it won't work if the O-ring is bad or the debris is really stuck. But for a quick, temporary, fix until you can get to a real repair...

 

[Rebel Lord]

Do you have a GATTS jar? If so, try opening the sump all the way and letting a good stream get going. Then close it by letting it spring back. That can often dislodge a bit of crud that might be the cause of the leak. Do that three or four times for good measure. Replacing still might be the best option, but this is a good temporary measure.

I tried that for like 10 minutes it was a solid stream and I kept messing with it until it was a consistent drip.

Take a rubber hose (say 1/4 inch ID), put it up against the sump drain, push the drain open while you blow into the other end. If the problem is a bit of junk under the O-ring, it may blow clear. Of course, there is no guarantee that the same bit of junk won't get stuck again at a later date and it won't work if the O-ring is bad or the debris is really stuck. But for a quick, temporary, fix until you can get to a real repair...

I will give this a try.

 

[Magman]

It’s not a bad idea to carry a spare valve.

Swapping is much cheaper than lost fuel and ruined tires.

+1 on rag around your wrist.

It helps eliminate the dancing contortions caused by fuel in the armpit on some!

 

[Gary Ward]

The sump valve is leaking on the Cherokee pretty bad. Is this something I as pilot can unthread and replace or do I need a mechanic?

My mechanic and I replaced one of mine , we rolled the plane out in front of the hangar and drained the tank into these 2 clean buckets to flush the tank and look for any water or dirt. Lucky there was none. I covered those buckets with baking trays and poured it back into tank when finished replacing the sump drain.

Mine were 7/16 straight thread and sealed with an o ring.

I did another on another 172 and did the quick swap with gas in the tank and running down my arm, I don't recommend doing it that way.

 

[kyleb]

Defueling scares the crap out of me. Too many stories of really bad things happening. I'd rather do (and have done) the "quick swap" while leaking a half-cup of gas on the ramp than defuel. Just my preference.

 

[Rebel Lord]

Defueling scares the crap out of me. Too many stories of really bad things happening. I'd rather do (and have done) the "quick swap" while leaking a half-cup of gas on the ramp than defuel. Just my preference.

Yeah I just went out and burned the tank down to about 2 gallons. Theres an old mechanic on the field I’ll probably have him do the swap.

 

[Magman]

My guess is few folks recall that many Cessnas did not have wing drains when new.

At the 100 & Annual you would pull the plugs . Rag around wrist helped.

The Owners Manual had wording that I considered backward.

IF you found water in the strainer located on the firewall THEN you would

pull wing tank plugs. Times have changed.


Cessna aircraft with bladders have a “Wing Shake “ technique required via AD unless modified.

When used on 172’s ( not required) I have found water at times.

 

[Dan Thomas]

Yeah I just went out and burned the tank down to about 2 gallons. Theres an old mechanic on the field I’ll probably have him do the swap.

You can run the tank down to 1/4 full or so. Turn the fuel selector to Off. Jack the opposite main gear or wing so that the remaining fuel goes to the outboard end of the tank, and replace the valve.

This works OK on airplanes with little dihedral, like the Cessnas. The Cherokees might need a lot of jacking or less fuel. Safer to drain the fuel.

 

[Magman]

Similar to Dan’s system; you can transfer a lot of fuel with selector in BOTH ( some in OFF) and

jacking one side. Then you can go to LEFT or RIGHT and jack other side to remove valve.

Note: Some Cessna POH or Owners Manuals specify when parking on uneven ground to go to LEFT

or RIGHT to prevent transfer .

 

[Dan Thomas]

Similar to Dan’s system; you can transfer a lot of fuel with selector in BOTH ( some in OFF) and

jacking one side. Then you can go to LEFT or RIGHT and jack other side to remove valve.

Note: Some Cessna POH or Owners Manuals specify when parking on uneven ground to go to LEFT

or RIGHT to prevent transfer .

That, too. I did that with a Commander 114 that had a seeping valve. I think that airplane had a Both position. Not common in low-wing airplanes. I did it in a Husky, too.

Won't work in a Cherokee. No Both position. The Cessna 150 has a simple on-off valve, and the fuel will transfer from one side to the other anyway. Most other Cessna singles have cam-operated selector valves that truly shut the fuel off in the Off position. I think some older models had plug-type valves that would transfer in Off, but those are limited to the '50s and early '60s, maybe.

 

[MRC01]

One more thing: there is a fuel resistant lube you can apply to the o-ring and threads before you install it. It can help the o-rings last longer and prevent threads from getting stuck.

EZ Turn Lubricant | Aircraft Spruce

EZ Turn Lubricant EZ Turn is a specialty lubricant/sealant used for fuel and oil line valves & is resistant to high temps. Especially effective where high octane fuels and aromatics are present. EZ Turn is also e...

www.aircraftspruce.com

 

[Palmpilot]

I once had a persistent stream develop in one of the sump valves of a rental 172 after refueling at an airport in southern Oregon. Fortunately, a mechanic was available on field to do a quick swap.

 

[Dan Thomas]

We used to change the flight-school airplanes' drain valves once a year. That avoided stuff like sticking or leaking drains far from home on some cross-country trip. If the valve was showing corrosion, it got tossed. Corroded valves can stick open, and if the spring in it isn't stainless, it can break and now the thing won't stay shut.

IIRC, the O-ring on the valve itself was an MS29513-006, and the one under the head of those with the 7/16" straight thread was an MS29513-012.

 

[kyleb]

We used to change the flight-school airplanes' drain valves once a year. That avoided stuff like sticking or leaking drains far from home on some cross-country trip. If the valve was showing corrosion, it got tossed. Corroded valves can stick open, and if the spring in it isn't stainless, it can break and now the thing won't stay shut.

IIRC, the O-ring on the valve itself was an MS29513-006, and the one under the head of those with the 7/16" straight thread was an MS29513-012.

Dan, you're a great resource. Thank you.

 

[Rebel Lord]

Said screw it and just did it, was a piece of red tank sealant lodged in the valve. Good as new now