Fuel Tank Test Advice (long-EZ).

[MikeD]

I’ve started to test the fuel tanks for potential leaks and have been getting mixed results. The tanks and the associated fuel lines have been sealed off and an altimeter attached then pressurised to 1500 ft. (as per plans). The results have been hard to interpret because of variations in temperature of my workshop (Boyles Law, Charles law… P1V1T1 etc.)

 

My question is:

 

Over what period should the system retain the pressure?

What is an acceptable pressure drop? if any.

Is there any other way of testing (e.g. using water instead of fuel)?

 

I really don’t want to move on to finishing other things and find I have a problem that requires undoing lots of work.

 

MikeD (U.K.)

[Lynn Erickson]

I’ve started to test the fuel tanks for potential leaks and have been getting mixed results. The tanks and the associated fuel lines have been sealed off and an altimeter attached then pressurised to 1500 ft. (as per plans). The results have been hard to interpret because of variations in temperature of my workshop (Boyles Law, Charles law… P1V1T1 etc.)

 

My question is:

 

Over what period should the system retain the pressure?

What is an acceptable pressure drop? if any.

Is there any other way of testing (e.g. using water instead of fuel)?

 

I really don’t want to move on to finishing other things and find I have a problem that requires undoing lots of work.

 

MikeD (U.K.)

any pressure loss is a leak. let it set for several days and it should read the same at a given temp. read it at the high and low pressure it should be the same after several days.

[Kent Ashton]

You can also use a water manometer for this. It takes about 20" of water differential to equal 1500' of altitude. It's about as much as you can blow with your breath.

 

If you have access to air-conditioning charging gear and a freon sniffer, you can charge the tanks with some freon ( or R134), pressurize and sniff around for leaks.

 

You can do the same with propane and a hydrocarbon sniffer. I just did this on my LEZ tanks. Charged the tank by squirting propane from a plumber's torch, pressurized and sniffed around with the propane sniffer. The sniffers are very sensitive.

 

I left the tanks pressurized overnight when I was building my Cozy but I think that's overcautious. If your tanks hold the same pressure for a hour or two with no drop in water level, they are tight.

[argoldman]

any pressure loss is a leak. let it set for several days and it should read the same at a given temp. read it at the high and low pressure it should be the same after several days.

 

What about if the Baro pressure changes also????

 

I like the sniffer Idea. Hopefully I will be able to borrow one when the time comes.

[steve]

I’ve started to test the fuel tanks for potential leaks and have been getting mixed results. The tanks and the associated fuel lines have been sealed off and an altimeter attached then pressurised to 1500 ft. (as per plans). The results have been hard to interpret because of variations in temperature of my workshop (Boyles Law, Charles law… P1V1T1 etc.)

 

My question is:

 

Over what period should the system retain the pressure?

What is an acceptable pressure drop? if any.

Is there any other way of testing (e.g. using water instead of fuel)?

 

I really don’t want to move on to finishing other things and find I have a problem that requires undoing lots of work.

 

MikeD (U.K.)

i just did this, if you can draw down to 1500 that is a very good sign, because if you had a hole 1/32" you'd lose all pressure in a fash.

get a cheep 10.00 temp reader from harber and read the tank and then see pressure.

[MikeD]

Kent, thanks for the idea. I've ordered a new propane sniffer (about $35) and will trying that method.

 

I agree with Lynn's post stating that any pressure drop with the same temperature is a leak. I've been unable to find the leak with the soap and water method.

 

I really didn't like the idea of filling the tanks with fuel to see where it was leaking. I'm about to recheck all the pipe work and fittings (if my wife allows me to do some canard work on Christmas Day:rolleyes: ) to make sure the problem is not in those components.

 

Just for interest, I have had the following results:

Pressured to 1500ft

 

1 hr - down to 1450ft (no temp or baro change)

2 hr - down to 1400ft (no temp or baro change)

3 hr - down to 1375ft (no temp or baro change)

 

Left it 24 hrs and brought the workshop temp back to the original, then waited for about an hour so the inside of the tank equalized in temperature.

 

24 hr - down to 750ft (no temp or baro change from previous day)

 

So you see, there’s a sneaky little leak in there somewhere just waiting for a tank full of 100L (Avgas) to cause some real heartache.

 

MikeD (U.K.)

[steve]

i just pump out all the air and brush wet epoxi all over the seems, then let the air back in. i use a vacuum hand pump and a hand made manometer

ace hardwere has 1/4" snap fittings and tee's.

[Cozy Girrrl]

Please do not do the propane thing again. If you have ever played around with the stuff you have some idea of its volitility This time of year the air is mighty dry, your plastic airplane is loaded with static and we'd hate to hear of any damage to your plane (or you). Seriously the smallest amount of propane in your tanks could be enough to blow the lid right off.

 

Freon is the best way to go because it has much smaller molecules and will easily leak from the smallest holes, a good leak indicator. Read the section on John Slades misadventures in canard building. He did this and found several holes, then an experienced regridgeration guy went over it and found a few more. Sometimes when you are hunting nits you need a professional nit hunter?

 

Regards, Chrissi

[MikeD]

Chrissi,

 

Point taken...

 

MikeD (U.K.)

[argoldman]

Please do not do the propane thing again. If you have ever played around with the stuff you have some idea of its volitility This time of year the air is mighty dry, your plastic airplane is loaded with static and we'd hate to hear of any damage to your plane (or you). Seriously the smallest amount of propane in your tanks could be enough to blow the lid right off.

 

Freon is the best way to go because it has much smaller molecules and will easily leak from the smallest holes, a good leak indicator. Read the section on John Slades misadventures in canard building. He did this and found several holes, then an experienced regridgeration guy went over it and found a few more. Sometimes when you are hunting nits you need a professional nit hunter?

 

Regards, Chrissi

thanks for the warning, Chrissie,

 

I was kinda hoping to use the propane as additional lightweight fuel but decided not to because of the odor.

 

Using Freon, I might be able to air condition my cabin.

 

Happy New Year!! to you and all

[Cozy Girrrl]

Long time ago I was replacing a burner valve on my yacht stove, doing the soap bubble test afterwards I still had a tiny leak. Being immeasurably young and stupid I decided to "see what would happen" if I lit this little bubble up, the "scientific method".

 

Okay, this is a very very minor slow leak, taking minutes to make a one inch bubble, I mean how much pressure could a soap membrane an inch in diameter contain, so hardly any propane, right?

 

Hey, I was smart enough to open the port above it and slide the main companionway hatch back, nice quiet still morning....

 

The "fireball" was about a foot in diameter

 

Never search for a gas leak with a match.

 

There are plenty of stories about boats in marinas where you'd see your typical Tupperware 30 with the whole deck sitting on the hull slightly askew as if it were somebody's partially completed kit, its always a case of the hull filling with a little bit of leaked propane and someone lights the stove. In most cases nobody is seriously hurt but the poof that happens is a bit of a shockwave an hopefully it is over and done with before anything catches on fire.

 

...Chrissi

[Big Steve]

Chrissi said:

The "fireball" was about a foot in diameter

 

I gotta tell you Chrissi you shure know how to party. STeve build on

[Cozy Girrrl]

Yah, sometimes I have a problem taking someone's word for it unless it comes to "wonder if that would hurt?" ...a chicken through and through

[airwrench]

thats one heck of a test to put on a yacht, wonder what would have happened if you allowed this one inch bubble to grow while you answered

the phone or something...........yachts in space/:rolleyes:

[Cozy Girrrl]

thats one heck of a test to put on a yacht, wonder what would have happened if you allowed this one inch bubble to grow while you answered

the phone or something...........yachts in space/:rolleyes:

uh no, as it was I ran the bilge blower for a long time as well as the pump. Propane sits and accumulates and when you have a bilge deep enough to stand in, thats a lot of volume.

" Yer going to the moon Alice! "

[MikeD]

Found the leak... As Kent mentioned in his post (You can also use a water manometer for this. It takes about 20" of water differential to equal 1500' of altitude. )

 

I made my own manometer and bought some children’s bubble stuff (I like playing with it too... pretty little bubbles floating in the air… ahem, get a grip on yourself ) and applied a thin layer with a small brush and presto… got it.

 

I couldn’t find it with ordinary soap and water mix and after all the advice about explosions etc. I thought I’d try a more sedate way (see attachments)

 

Many thanks for all the advice.

 

MikeD (U.K.)

[TMann]

I ran accross this on the CA list and thought it deserves to be posted here as well. Interesting method for detectling leaks:

 

A long while ago, one of you wrote of a method for locating pin hole leaks on starkes.

 

As I remember it, you take a rag saturated with a ammonia, stuff it into the fuel tank via the filler and after a short period, rub the outside of the strake with a rag soaked in Phenolphthalein. Upon hitting a wiff of ammonia the rag turns pink.

 

You then hook up a low vacuum source to the strake and paint the tinted area with thinned epoxy until the hole seals.

 

[Cozy Girrrl]

"As I remember it, you take a rag saturated with a ammonia, stuff it into the fuel tank via the filler and after a short period, rub the outside of the strake with a rag soaked in Phenolphthalein. Upon hitting a wiff of ammonia the rag turns pink. "

 

If I remember correctly from grammar school days; its also a wicked laxitive