Fuel Drain Valve

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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dstclair
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Fuel Drain Valve

Postby dstclair » Mon May 02, 2016 8:27 am

My fuel drain valve does not consistently seal on release after doing my fuel check. It's typically only a slow leak of droplets that I can fix by resumping and/or manually pulling the spring down. This past week I almost didn't get it to stop leaking so I figure its time to replace. My importer suggested one of two parts:

* SAF-Air 1250 Image
* Curtis 1250 Image

I have the Curtis. Any preference? Or just pick one as they're all alike :-)

Also, these are NPT threads and the STC calls for a sealant. Which thread sealant do I use?
dave

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Re: Fuel Drain Valve

Postby roger lee » Mon May 02, 2016 8:29 am

Curtis is one of the more popular ones. Aircraft Spruce has a good selection of these and others.
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designrs
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Re: Fuel Drain Valve

Postby designrs » Mon May 02, 2016 8:43 am

My airplane had slow drips after sumping. My A&P told me to turn the sump a little while pushing in to reseat the seal. Results were mixed. Not ready to be replaced, but always triple-checked before flight. Persistent and intermittent nuisance. THEN I started using Corrosion X on my aircraft including the exterior metals of the sump. (Applied with a small brush.) It lubricates and prevents corrosion. NEVER had a drippy sump again!
Last edited by designrs on Mon May 02, 2016 8:52 am, edited 2 times in total.
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MrMorden
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Re: Fuel Drain Valve

Postby MrMorden » Mon May 02, 2016 8:44 am

Seems the Curtis would be easier to manipulate with a fuel tester. With the other, draining fuel will be a two-handed operation.
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3Dreaming
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Re: Fuel Drain Valve

Postby 3Dreaming » Mon May 02, 2016 8:53 am

If you feel that you must use a sealant, I would use something non hardening like the white Teflon paste. Be aware that the sealant will make it easier to over tighten the fitting making it a real problem to remover next time. If the fitting is going into metal I normally install it dry.

The big difference between the two valves are, the Safe Air has replaceable O-rings for future maintenance. Curtis on the other hand has a special flat seal designed for their valve, and it is not field replaceable. This means next time it is leaking you replace the valve again. From a maintenance stand point the cost of the valve and labor to replace O-rings about equals out.

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dstclair
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Re: Fuel Drain Valve

Postby dstclair » Mon May 02, 2016 9:15 am

3Dreaming wrote:If you feel that you must use a sealant, I would use something non hardening like the white Teflon paste. Be aware that the sealant will make it easier to over tighten the fitting making it a real problem to remover next time. If the fitting is going into metal I normally install it dry.

I was just going based on "Maintenance Tips" from one of the suppliers:

Curtis Superior and SAF-AIR valves are
designed for installation in a standard NPT
port for NPT threaded valves or an
AND-10050 style port for UNF threaded
valves. Use a sealant on NPT threaded valves
or a fuel resistant o-ring of the proper size
for UNF threaded valves.


I'd be fine not using sealant if that's the norm.

Edit: Just found the section in my maintenance manual and it says "Use Locktite 565 for replacement".
dave

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drseti
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Re: Fuel Drain Valve

Postby drseti » Mon May 02, 2016 9:58 am

If yours is an SLSA, Dave, the maintenance manual is regulatory. If it's an ELSA, using the same Loctite it calls out is still a pretty good idea.
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dstclair
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Re: Fuel Drain Valve

Postby dstclair » Tue May 03, 2016 9:22 am

Just in case someone is searching -- turns out the part is the 1550 (not 1250).
dave

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dstclair
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Re: Fuel Drain Valve

Postby dstclair » Mon Sep 05, 2016 6:12 pm

Well, my saga continues....

I bought the replacement Curtis CCA-1550 and it would only screw in about 1/3 of the way before it bound pretty tight. The old one screwed in relatively easily. I splurged and spent another $12.50 and bought another new valve. It has the same issue as the other new one. I did clean up my 'old' one and it worked fine for about 2 months but it's now having issues. I have double (triple, quadruple, etc) checked the part number on all 3 and they are stamped identically.

Any ideas on getting the new one screwed all the way in?
dave

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FastEddieB
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Re: Fuel Drain Valve

Postby FastEddieB » Mon Sep 05, 2016 6:48 pm

eyeflygps wrote:I think there are tools you can use to correct this.


Yes. The right sized tap can be used to "chase" the threads, if that is indeed the problem - i.e. cross-threading.

Sounds feasible, but tread carefully - you don't want to further bugger up the threads if that is the problem.
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Re: Fuel Drain Valve

Postby 3Dreaming » Mon Sep 05, 2016 8:12 pm

You are dealing with tapered threads. The drain valve cross section gets wider as it screws in, while what you are screwing into gets smaller. They are supposed to get tight. The valve is made of brass, and it will give a little when it gets screwed in. Try finding a brass pipe bushing with a female 1/8" pipe thread hole. Screw the fitting good and tight, then back it out. Now try re-installing it in the airplane. If it comes down to it you can clean the threads on both sides with a 1/8" pipe thread tap and die.

An other option is to order a replacement seal for your old valve. Curtis doesn't like for them to be changed in the field anymore, but you can get seals. http://www.mcfarlaneaviation.com/Produc ... CACCA1269& I think the one you want is CACCA1269.

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Re: Fuel Drain Valve

Postby 3Dreaming » Mon Sep 05, 2016 8:53 pm

Having installed several of these valves over the years. I wouldn't worry about the new valve not screwing in as far as the old one, as long as there is enough thread engagement for it to be safe and seal up.

av8tor
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Re: Fuel Drain Valve

Postby av8tor » Tue Sep 06, 2016 7:22 am

Had the same problem. A shot of WD-40 and a few compressions fixed it.

roger lee
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Re: Fuel Drain Valve

Postby roger lee » Tue Sep 06, 2016 9:35 am

These are NPT tapered threads. It will stop and seat on it's own. Not every valve may stop threading at the exact same point and especially if it is a different brand. 80 in/lbs is okay on this tapered thread or just make it snug. Your main goal here is to not have it leak. Do not try and wrench this in deeper than it is supposed to. You'll either trash the receptacle threads or worse yet split it.
Roger Lee
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drdehave
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Re: Fuel Drain Valve

Postby drdehave » Sat Sep 10, 2016 6:10 pm

Dave:

1. Yes, Curtis Drain Valve CCA-1550 IS the correct one for our earlier Stings.

2. The MM calls for it to be sealed with Loctite 565--and I found that makes it easier to screw in and seat.

3. This valve dribbles and weeps for one reason: Because of gentle pushes up to get a small drain sample, followed by a gentle release down to the closed position. The remedy is quite simple. Whenever you take a sample, LOCK the valve in the open position. Then, when you're done, SNAP it smartly shut to the closed position. This compresses the "O" ring sufficiently that it will not leak--period! The valve will then last forever--although at a mere $12.50 a pop, I do carry one and the Loctite 565 with me at all times (but have not needed it in 2,000 hours).

4. Locking it open for a healthy fuel sample (at least 1/2-1 pint, whilst rocking the wings) is something you should be doing anyway, before first flight of the day, and after last flight of the day, given the Sting's history of fuel tank delamination (and just various fiberglass debris and resin). Sump a pint mason jar full, hold it up to the sunlight, and swirl it in a circular motion. You'll be glad you're removing fiberglass gunk that won't then have a chance to make it to your gascolator, where it could result in fuel flow impairment.

Rich
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