Weeping Drain Valves

[skippydiesel]

My Sonex wing tanks have SAF-AIR push type fuel drain valves.

They leak or rather they weep very slowly.

The whole aircraft, including valves, have only done 185 hrs in about 2 years and the valves have been leaking for most of that time.

I make a point of pulling each one down after every preflight drain – doesn’t help.

The weep is so slow that this is more of an aesthetic problem – stains on my wings, than any practical issue.

All helpful suggestions welcome😈

[rodgerc]

Tena pads or Depends if it’s only minor leakage. 

Edited Friday at 07:48 AM by rodgerc

[djpacro]

17 minutes ago, skippydiesel said:

My Sonex wing tanks have SAF-AIR push type fuel drain valves.

They leak or rather they weep very slowly.

I've had the same problem with new drain valves. Take them out and clean them - dirt or a burr is enough to open them enough to leak. Have a friend with you to stick their finger in the hole or have a plug (perhaps an old valve) ready to screw in.

[facthunter]

I usually just give them a few twists each way while holding them DOWN if they are the Item I'm thinking of. Nev

[skippydiesel]

29 minutes ago, djpacro said:

I've had the same problem with new drain valves. Take them out and clean them - dirt or a burr is enough to open them enough to leak. Have a friend with you to stick their finger in the hole or have a plug (perhaps an old valve) ready to screw in.

Or use up all the fuel - just topped up the tanks today, so will be a while before empty.

 

This should not happen though - must be a crap design if so easily defected.

 

Will try your suggestion - nothing to lose except the staines and very slightly lower fuel consumption.😈

[facthunter]

 Remove and have a Plug or cork ready and clean and Lap it, then put it back in. Do you Filter your fuel or is there any sediment showing in your drain sample.  Nev.

[Blueadventures]

Don't fly while dripping fuel leak under a plane, back fire on start up, small pool of evaporating fuel and light breeze wrong way and you have a fire possibility.  Happened at Proserpine to an RAA aircraft a few years back.  I don't like the push up steel (get rusty) ones, not uncommon to leak and need replacing.

Edited Friday at 10:08 AM by Blueadventures

[Moneybox]

You most likely have a bit of sediment in the tank. Try opening them fully a couple of times to hopefully flush it enough to seal the contact area.

[BrendAn]

I replaced my Curtis valve. Not cheap at $54 but now it's always dry under the plane. Used to be greeted by a big wet patch on the floor each weekend. Didn't like that when av gas is $2.80 p/l

[Thruster88]

I would buy a replacement, $30-50 aussie from aircraft spruce australia. Depending on which type you have the o-ring could be replaced and you will have a spare. The flush, cessna style, look like they are sealed for life.

[skippydiesel]

12 hours ago, Blueadventures said:

Don't fly while dripping fuel leak under a plane, back fire on start up, small pool of evaporating fuel and light breeze wrong way and you have a fire possibility.  Happened at Proserpine to an RAA aircraft a few years back.  I don't like the push up steel (get rusty) ones, not uncommon to leak and need replacing.

Thats an ATEC Zephyr and the initial fire is concentrated in the engine bay - not the fuel tank area.😈

[skippydiesel]

11 hours ago, Moneybox said:

You most likely have a bit of sediment in the tank. Try opening them fully a couple of times to hopefully flush it enough to seal the contact area.

Shouldn't have but wont discount completly;

• Tanks were well flushed before test flights.
• ALL fuel is passed through a Mr Funnel
• In 195 hrs, no contaminants appear in pre flight fuel drainings

I have tried a prolonged drain/flush  no improvement. 

 

Next time tanks are empty, will remove drain valves and attempt a clean - see what happens.😈

[skippydiesel]

1 hour ago, Thruster88 said:

I would buy a replacement, $30-50 aussie from aircraft spruce australia. Depending on which type you have the o-ring could be replaced and you will have a spare. The flush, cessna style, look like they are sealed for life.

These are new valves - they should not need to have the o-rings replaced but if all else fails I will certainly replace them in the hope of a fix😈

[skippydiesel]

12 hours ago, BrendAn said:

I replaced my Curtis valve. Not cheap at $54 but now it's always dry under the plane. Used to be greeted by a big wet patch on the floor each weekend. Didn't like that when av gas is $2.80 p/l

What did you replace the Curtis valves with?😈

[BrendAn]

52 minutes ago, skippydiesel said:

What did you replace the Curtis valves with?😈

Another Curtis valve. Genuine Curtis brand

[Moneybox]

1 hour ago, skippydiesel said:

These are new valves - they should not need to have the o-rings replaced but if all else fails I will certainly replace them in the hope of a fix😈

 Try to buy the ones with a male thread. Excessive weeping is usually a female trait. 

[facthunter]

Jesus Wept.  Nev

[Blueadventures]

For forum members information (excluding Skip because he is always negative and won't believe this is correct).  The leaky fuel tank drain has flames at it, burnt grass area to starboard side of front end as that's where the vapour would have been going (refer smoke plume drift).  Ignition occurred and source spread, prop wash extinguished grass fire but not the aircraft fuel areas.  Owner was seated in cockpit doing a start to provide an engine run (wing cover on and still tied down).  When fire observed he made a radio call to alert airports fire rescue, they don't monitor outside of RPT, he made further communication to ARO and operator about this.

[Moneybox]

36 minutes ago, facthunter said:

Jesus Wept.  Nev

I never read that book...

[facthunter]

The shortest sentence in the Bible. I didn't finish it either as someone  told me how it ended. Nev

[facthunter]

Getting back to the drain Valves. I don't like relying on a spring OR an "O" ring. The drain VALVE(s) should all be located in the Lowest parts of the section they drain from and would frequently be in contact with water making steel unsuitable for the seating Parts, long term. Nev

[skippydiesel]

On 17/01/2026 at 11:52 AM, Blueadventures said:

For forum members information (excluding Skip because he is always negative and won't believe this is correct).  The leaky fuel tank drain has flames at it, burnt grass area to starboard side of front end as that's where the vapour would have been going (refer smoke plume drift).  Ignition occurred and source spread, prop wash extinguished grass fire but not the aircraft fuel areas.  Owner was seated in cockpit doing a start to provide an engine run (wing cover on and still tied down).  When fire observed he made a radio call to alert airports fire rescue, they don't monitor outside of RPT, he made further communication to ARO and operator about this.

Hi Blueadventure,

 

How about you quote me an example(s) where I have been "always negative" - If unable to do so, the proper thing would be to post a retraction/apology.

 

As for not "beleiving this is corrcet".

I have an idea I might know of the pilot & the incident.

If memory serves the fire started in the engine bay/under cowl - not from a leaking fuel tank.

The fuel tank is located, in the Zephyr, under the pilot/passenger legs, roughly just in front of the main undercarriage.

The tank fuel drain is at the lowest point of the fuselage directly below the tank.

You can see, from the photo you posted, where the fire has had its main impact, the the engine bay (at the time of the photo).

The fuel tank area is (at the time of the photo) untouched.

There is no obvious scorching of the grass, flames or any indication of fire, in the area under/around the aircraft.

I was not a witness to the event. If you were and you stand by your statements above (despite the photo evidence) then I accept your word with some scepticism.😈

[skippydiesel]

In the mean time I have been trying to track down details of my Saf-Air wing tank drain valves.

 

Part Number CAV-110, Thread Size 1/8-27 NPT. O Ring Viton Compound M83248/1-006 

 

Saf-Air list them as brass.  Aircraft Spruce as cadmium coated steel - have writen to NZ agents seeking clarification (& some prices).

 

Prices so far;

 

Aircraft Spruce - Valve $32.45, O rings $0.64/each (show 10 pack so may be $6.40)

Pilot Gear - Valve $31.95

😈

 

 

 

 

 

[facthunter]

Some CADMIUM Plating looked like Brass. Cadmium Plating has been Banned in some Places. Cadmium is dangerous The Alternative in Aviation is Zinc-Nickel. That's been the case for Many years Electroplaters have a hard time with EPA's. MOST have gone out of business. . Zinc gives Galvanic Protection.  (sacrificial).  But it is soft.  Nev

[djpacro]

51 minutes ago, skippydiesel said:

Saf-Air list them as brass.  Aircraft Spruce as cadmium coated steel - have writen to NZ agents seeking clarification (& some prices).

Spruce here specifies brass. https://www.aircraftspruce.com.au/catalog/appages/safaircav110.php?clickkey=4324