Tip: Priming tubes/weldments

[wirejock]

Priming tubes.
Sometimes the bear gets you. Sometimes you get the bear. Today, I got the bear.
Almost every airplane has a tube or weldment and often they need to be primed inside. If you're like me, you struggle with sealing the end and inevitably more primer ends up on the floor than inside the tube. I've tried all sorts of plugs and tape with questionable results. My shop floor is evidence to my failure.

Most of us have a box of Nitrile gloves. Turns out they work for more than keeping your hands clean.
Cut the fingers off a glove or two. Choose the fingers that fit nice and snug. Pinky fingers work for smaller tubes. Thumbs work for large tubes. For this job, I used the middle fingers.
The gloves are usually dusted inside with powder to make them slide on easier. The powder will allow the finger to slide off.
Slip a finger over the tube but make sure the outside surface of the glove is the side against the surface of the tube.
Place the gloved end of the tube in a bucket. No reason to temp fate. Pour in the primer then slip another glove finger over the open end. Remember, inside out.

Slosh the primer back and forth while rotating the pipe. A minute or two or at least two rotations is plenty. Stand it on end over the bucket again. Slide the top finger off and pour the contents into a paint cup. Stand the pipe open end down in a bucket to catch the remaining primer and slip the finger off the sealed end.
No mess! Wish I had thought of this one several messes ago.

[tgmillso]

Nice one Larry. About to move onto prime a bunch of tubes because today I'll finally be wrapping up my fuel tanks (I was beginning to think this day would come). Your timing for this post is impeccable.
Cheers.
Tom.

[AdamB]

How symbolic that the middle finger of the glove fit this particular job!
Looks like you showed it!

[wirejock]

Originally Posted by AdamB

How symbolic that the middle finger of the glove fit this particular job!
Looks like you showed it!

I wondered if anyone would notice.

[JanRV6UK]

I have often wondered how effective it is to put primer inside a tube that is not properly cleaned ... how do you know that the primer will stick to the wall ??

I know a lot of people will have far more experience in this than I do .... but my understanding with respect to 4130 tubing .. in the good old days ... the welder would slosh the tube with Linseed oil ....

Today .. maybe something like Ardrox AV8 would be more appropriate ... Ardrox AV8 works for both steel and alu ... https://www.silmid.com/products/dina...ive-1lt-i.aspx

Just a thought ....

[JonJay]

Do the instructions call out priming inside the weldments like the rudder bar?
Obviously you can't prime inside the rudder stirrups as they are welded shut.
I know they call out priming for pushrods. Just curious.

As Jan points out, in the day, a hole was drilled, linseed oil was inserted and sloshed around and then the tube welded up.

[wirejock]

Originally Posted by JonJay

Do the instructions call out priming inside the weldments like the rudder bar?
Obviously you can't prime inside the rudder stirrups as they are welded shut.
I know they call out priming for pushrods. Just curious.

As Jan points out, in the day, a hole was drilled, linseed oil was inserted and sloshed around and then the tube welded up.

Interesting question
No. There is no instruction for priming the inside of the rudder or flap weldments.
But, the fuse instructions are less detailed. I figured it wouldn't hurt.
As a side note, my idea is just a method for putting a liquid in the tube. Feel free to use whatever protectant you like. I actually sloshed lacquer thinner in them, let them dry over night then poured in SWP60G2.

[MElstien]

I am getting to that part on my build for the elevator push tube. Couldn't you alodine them or have the alodined? Is there a need for primer on the inside since once sealed up, there is no way to ruin the alodine protection. A dip would work on the outside as well and then prime the outside.

Just curious?

[wirejock]

Originally Posted by MElstien

I am getting to that part on my build for the elevator push tube. Couldn't you alodine them or have the alodined? Is there a need for primer on the inside since once sealed up, there is no way to ruin the alodine protection. A dip would work on the outside as well and then prime the outside.

Just curious?

It's an aluminum tube so alodine would work fine. The only trick is prepping to alodine. You want to Alumiprep since it can't be scotch brite scuffed easiely. Then rinse and alodine.
I suppose if you had a PVC tube, you could use it to Alumiprep dip the tube then again to Alodine and both inside and outside would be done.
YMMV