tips for reinstalling fuel selector without spilling avgas everywhere

[Vance Harral]

Our fuel selector is at LASAR right now for overhaul.  Removing it from the airplane was a fairly miserable experience.  Despite my best "quick draw" routine, fuel rained all over me from the time I first loosened the lines from the tank until I got a plug installed.  Twice, of course - once for each side.

When it comes time to reinstall, I'm wondering if there's a trick to make the job easier.  In particular, I was thinking of trying to draw a (very) light vacuum on the tanks from the fuel tank vent.  I have a little hand-operated vacuum pump and could attach it to the vent with some tubing.  If anyone has tried this or has some other tip, I'm all ears.

[ArtVandelay]

You can empty the tanks if you have storage?

[carusoam]

Stop

Think

Plan

+1 on emptying the tanks... 

Vance, consider the following....

Drawing fuel vapor into a vacuum cleaner's motor can be a really flame throwing bad idea.  

assess the risk you are taking on....

Do one side at a time if it helps.

Fuel is too dangerous to be showered with it.  

A fire started by fuel running on the ground spreads pretty far, quickly...

The injury caused by fire is pretty severe.

The people affected by it don't usually realize the significance before hand.

grounding everything as you go.  Dry winter air can add to the challenge.

a young mechanic at my home drome, accidently opened a fuel tank with a powered driver.  That didn't end well...

Proper fire extinguishers nearby..?

Hoping this message aids the thought process.

Best regards,

-a-

Edited February 4, 2017 by carusoam

[Vance Harral]

Yes, all the caution you mention is appropriate and I appreciate it.  That's why I'm asking for ideas here on the forum - to increase safety, not just to make the job easier.

Draining the tanks isn't impossible, but highly impractical given the particulars of the shop, and has it's own risks to boot.

To be clear, my vacuum idea involves a hand operated vacuum pump, of the type you'd use to bleed brakes.  No motor, no electricity of any kind.

I did ground the airframe and I know where the extinguishers are.  I employ the buddy system with the shop mechanics to minimize risk.

[thinwing]

Stop the second guessing...drain the tanks!..All the way....

[Guest]

Having had my own airplane on fire in my hangar, I'll say de-fuel it.  

Pour some 100LL in a drip tray outside, throw in a match then see how long it takes to put it out.  Now imagine that your shirt is soaked and you're on fire and the fuel just keeps on pouring out of the open lines.

Clarence

[Bob_Belville]

I have no quarrel with the advice to empty the tanks. Sounds like the prudent thing to do. 

However we overhauled my fuel selector last year and Lynn capped the fuel lines from the tanks as fast as possible. Probably had an ounce or 2 drip into a coffee can each time he uncapped/capped a line.

[INA201]

We drained the tanks to do it and had no issues. It's a pain to get the valve up in there as it is.

[M20F-1968]

Do not even consider doing the work without draining the tanks fully.  Handling fuel is dangerous as are its vapors.

Go to Home Depot and get several 5 gallon pails with screw-on sealing covers.

Ground the airplane, be careful about generating static electricity.

Take out the fuel drain in the wing and fill each 5 gallon pail.  6-7 will drain each wing.

Install the fuel selector.

Reinstall fuel drain and refill tanks.  Use a funnel with a screen to refill (there are some that extract water as well - see Mr. Funnel on amazon.com).

There are NO short cuts to this project.

John Breda

 

[N201MKTurbo]

I've done it a few times. If you think about it and plan what you are going to do you can do it with only a few ml  spilled. There is a risk of uncontrolled fuel spillage so you will have to make your own assessment.

loosen the B nut on the plug holding the plug against the end of the tube. When the B nut is completely off the plug push it off with your finger capping the tube with your finger. Then slide the tube off of your finger onto the fitting on the fuel selector and press the tube tight against the fitting then spin on and tighten the B nut.

it is best to do this with someone else around in case your plug or wrench or something rolls away.

[Vance Harral]

Just to follow up... when it was time to reinstall the fuel selector, the A&P offered to do it, and I said "be my guest".  He didn't drain the tanks, but opted for the quick-draw routine instead.  I made sure the airframe was grounded and stood by with a fire extinguisher.  I respect the opinion of those who think this is excessive risk, each owner and mechanic must make their own decision.

For others reading the thread... the thing that makes this a bear in a Mooney is that the fuel selector is in tight quarters.  The nearby structures, the plugs being installed/removed from the lines, and the fuel selector itself, all tend to get in the way of each other.

[Sean S]

A hand operated vacuum would have helped in a pinch. 1-3 inches on the tank vents will help keep the spillage to a minimum. The best alternative is the empty the tanks. Good that you got it done and all is well!

[RobertGary1]

On 3/7/2017 at 2:06 PM, Bayern Speed said:

A hand operated vacuum would have helped in a pinch. 1-3 inches on the tank vents will help keep the spillage to a minimum. The best alternative is the empty the thanks. Good that you got it done and all is well!

I'm skeptical a hand pump can move though air to generate a vacuum in a void as large as a fuel tank. 

-Robert

Edited March 9, 2017 by RobertGary1

[Andy95W]

6 hours ago, RobertGary1 said:

I'm skeptical a hand pump can move though air to generate a vacuum in a void as large as a fuel tank. 

-Robert

Actually, I think I believe it. A 1 foot high column of water exerts only .433 psi pressure. Our Mooney fuel tanks are only about 1 1/2 feet vertical and the fuel tubing is probably only about 3/16" round ID, or about 1/20 of a square inch so less than 1/2 psi should certainly do it. My math may be wrong, however. 

[carusoam]

Some gas law says if you remove the air, the pressure will decrease.  No matter how small or slow or strong the pump is...

PV=nRT

The challenge to generating any vacuum is the air entering the system either through leaks or the tank's vent. Or, if you decided not to empty the tank, putting a vacuum on it may cause the fuel to evaporate/boil to fill the empty volume with vapor.  This becomes a related rate problem of balancing the rate of evaporation with the rate of the pump generating a vacuum... (that leads us to another part of the gas law... Nature abhors a vacuum)

+1 for emptying the tank first...

an example of removing a volume of gas from the tank at a rate of 10gal per hour with the tank's vent sealed off by a dirt dauber nest.  The tank will try to oil can as the fuel pump fights to deliver fuel.  That's a lot of vacuum...

reminder, vacuum can probably be relieved by opening the cockpit fuel drain...?

Too much vacuum, may not be good for the existing old sealant either...

See if that helps... 

Best regards,

-a-

Edited March 9, 2017 by carusoam

[Bob_Belville]

We simply block the vent which slows the outflow. Pouring gasoline from a 5 gallon can gives an idea of the effect. The smaller the orifice the more effective the lack of a vent is.

[mooniac15u]

1 hour ago, carusoam said:

Some gas law says if you remove the air, the pressure will decrease.  No matter how small or slow or strong the pump is...

PV=nRT

The challenge to generating any vacuum is the air entering the system either through leaks or the tank's vent. Or, if you decided not to empty the tank, putting a vacuum on it may cause the fuel to evaporate/boil to fill the empty volume with vapor.  This becomes a related rate problem of balancing the rate of evaporation with the rate of the pump generating a vacuum... (that leads us to another part of the gas law... Nature abhors a vacuum)

+1 for emptying the tank first...

an example of removing a volume of gas from the tank at a rate of 10gal per hour with the tank's vent sealed off by a dirt dauber nest.  The tank will try to oil can as the fuel pump fights to deliver fuel.  That's a lot of vacuum...

reminder, vacuum can probably be relieved by opening the cockpit fuel drain...?

Too much vacuum, may not be good for the existing old sealant either...

See if that helps... 

Best regards,

-a-

Evaporating fuel will only contribute to the pressure in the tank up to the fuel's vapor pressure which is less than 1 atm.