How to: Leak detection 3

[Perd]

We are at a bit of a dead end here needing some ideas on which direction to pursue.

We are building a unit that is required to be water tight. It should be able to withstand being submerged in a meter of water for 30 minutes without water passing any of the seals.

The problem we are currently experiencing is this:

There are 26 seals in the unit with several having the potential to leak. The best method we currently have to detect where a leak is occurring is to apply positive pressure to the unit with helium at about 0.5 PSI. We then use a handheld helium detector and sniff around the unit to determine where the helium is leaking. Obvious problems here are if we set the detector to detect even the smallest amount of helium it detects false fails as very small amounts of helium pass through the seals. The other problem is the test is very time consuming and often does not catch all of the leaks the first or second time so we are spending manufacturing time pulling the units apart several times before they eventually seal.

The only other method we have used is applying positive pressure to the unit and dunking it in a tank of water to see where the leaks come from. This is not what we want to be doing at $3000+ per unit. The risk of damaging the internal electronics is high.

Anyone have any experience or ideas on this subject. We have been kicking around the idea of trying to use some type of thermal imaging camera but I am no chemist so we haven't really figured if any type of gas would work well to inject and use the thermal camera to detect leaks.

Thanks for any help/suggestions.

 

[btrueblood]

"Snoop" is just detergent and water, with a little glycerin added (make sure you rinse it off with clean water, or it gets really sticky). Same formula used in soap bubble solution that you buy at the dollar store for kids, only snoop has more water. Cost for "bubble juice" is < $1 US for 8-oz. container, a savings of $11 (more if you dilute the bubble juice). Hmmm, shoulda kept that to myself, and sold relabelled "Snoup" solution on ebay. Rats.

 

[Pud]

In a previous life, we used to this kit for leak testing domestic gas appliances. Took about 10 seconds each if I remember (on an assembly line):

http://www.furness-controls.com/products/leak-detection/fco284/

A quick discussion with them (as leak test experts) might be fruitful...

I would have thought helium a poor choice to test for water leaks - the stuff will leak through anything due to it's low molecular size! (e.g. party balloons in hours)

Cheers


Harry

 

[unclesyd]

I would look at colorimetric leak detection for your system. Aside form the tracers (gases) mention is the American Gas Chemical articles there are additional materials that will work.
You will note from that soap solutions are out of favor and in most cases not acceptable.

Though there are many others AmGas covers the field when it comes to practical leak detection as far as I'm concerned. I would give them a call.

http://www.amgas.com/ldrefpage.htm

http://www.amgas.com/large_containers.htm

http://www.amgas.com/clmwhite.htm

We used NH3 as a tracer for leak detection on equipment used in Therminol service and our high pressure hydrogenation equipment.

 

[Philrock]

Make a rigid, watertight test tank that totally contains the device to be tested. Have a clear 1/4" diameter standpipe sticking out the top surface of the test tank and up 1 meter higher than the top of the device under test. Put the device in the test tank. Close and seal the lid. Fill the test tank with water until it overflows out the top of the standpipe. If the water level in the standpipe goes down, water has leaked into the device under test.

Note - this is a very sensitive test - volume changes due to thermal expansion/contraction will be easily observable, so you won't have valid results until everything has reached thermal equilibrium.

If small leaks are possible and are likely to cause expensive damage, this might not be a great approach.

 

[svanels]

I would use a portable ultrasound detector (ue systems or SDT)

1) With the ue systems ultraprobe you have a small warbletone generator (battery operated), put it in the box and scan the seals from the outside. (very fast !!!)

2) Put air pressure on the box, and scan from the outside if something coming out (also fast)

At least compressed air is cheaper than helium, and the sensor is much more sensitive.

 

[HDS]

http://www.pressurex.com

Fuji film works good for trouble shooting this kind of problem with leaks on seals.

As other have said He will leak into and through rubber and silicone seals that will hold water forever.

Can you use a product like green locktite to make a permanent seal on some of the locations?

 

[Newmanite]

pressurise it as you see fit and walk around all 26 seals with some water and dishwashing liquid mix. squirting on the seals.If a bubble forms you have a leak if it doesnt you do not.

 

[polleke]

Hi Perd,

I have used the Ultrasonic Detector SDT170 in several situations with good result.
Even a verry small Freon leak was detected.
You can find information at:

http://www.sdt.be

The principal of the detector is that every leak produces an ultrasonic sound.
So pressurise your unit and check it with the detector

succes

Harry