Helium gas can be used for detecting leaks in embedded or buried pipes when other detection systems fail. Not all broken tubes will make a sound, so sound machines do not work all of the time. Sensitive heat sensors require enough hot water to leave the broken pipe to form a large enough area to detect a difference. Helium can exit any break in a pipe, float to the surface and be detected. The helium method excels on very small breaks and broken tubes located under bath tubs, shower stalls, walls, cabinets, fireplace hearths or just about any place an installer might lay them in the slab.
Some facts on helium gas that make it a prime candidate for detection
a. helium is the second smallest molecule
b. helium is lighter than air so it will rise
c. helium is non toxic, inert and only 5 parts per million in the atmosphere.
d. helium can travel through concrete, carpet, carpet pad, tile floors, wood floors (sheet vinyl is a little more difficult)
To save a tremendous amount of time and to do a quality job it is necessary to have a piece of equipment that can read at least 50 parts per million. The helium detector has a vacuum pump which "sniffs" (draws in) the helium content of the air by passing it through a crystal. The amount of helium detected is read out on a digital display in parts per million. Machines that can only read down to 200 to 300 parts per million are considerably less expensive but will not be able to locate half of the broken tubes and require covering every square inch of floor space. Machines that can read at least 50 ppm can cover 1,000 sq ft in under thirty minutes. Try before you buy. Varian was one of the few companies that loans use of a machine in the field for several weeks. Most machines are over 100 pounds in weight. Varian was the first to produce a lightweight battery machine that had the same specifications as the heavy ones. They have a battery operated machine that only weighs about 12 pounds, can read 10 parts per million. The Varian Vac Product National Sales Center can be reached AT (800) 882-7426
Note: The instruments developed by Varian and other companies primarily service the microchip and semiconductor industry. Another large user group is telephone companies who need to find leaks in wire insulation.
The initial cost of the unit mentioned in this article is approximately $7,000 plus attachments. Fortunately for those who only need the use of a machine occasionally Varian will rent out their machines.
Broken tubes are generally found where concrete cracks; therefore, it is easy to pin point these types of breaks because the helium is able to travel up through the open crack. Pipes leaking due to electrolysis and corrosion can be anywhere in the slab; thereby, taking a little more time to locate because the helium generally has to work its way up through the solid concrete.
1. Leak Test
Do a hydrostatic test to determine how much water is leaking out of the system.
2. Remove Water
Remove the water from the radiant floor tubing. I have found using compressed nitrogen gas bottles have been the best way to remove the water. This works better than air compressors. Remove the pump and replace it with two matching flanges that are fitted with hose bibs. Put a garden hose on one hose bib and attach the nitrogen bottle to the other. Open and close zone valves and balance valves to insure that as much water is removed as possible. If the boiler has to be by-passed, tap into the system by removing the unions and installing hose bibs on the system side of the piping.
3. Don't Rush
FROM THIS POINT ON DO NOT BE IN A RUSH!... if you saturate under the slab and fill the building with helium gas, you will not be able to pin point anything.
4. Fill With Helium
Fill the system with helium gas, the pressure will be based on the amount of water leaking out of the system. Start small. Charge the radiant system with 5 psi of helium for leaks that are losing 4 oz. or more of water in 30 seconds. DO NOT try and maintain a constant pressure in the system, because the area around the broken tube will become saturated before the helium reaches the surface.
5. Use Detector
Pass the detector over the floor while watching the LED indicator. A rapid increase in parts per million will indicate the location of a leak.
6. Fix Leak
When a broken tube is located, stop and fix it. Then pressurize the system again and look for the next broken tube (I always assume there is one more broken tube, it will save a lot of time in the long run).
7. Continue Search
As breaks in the tubes get smaller it will be necessary to increase the pressure. After the first hour or the first broken tube is located (which ever is first) start increasing the pressure 10-15 psi every 15 to 20 minutes. The majority of leaks are found between 0-50 psi. The highest I have gone is 125 psi. There are a lot of judgment calls to be made in this process because each floor and building is a little different.
8. Leak Test
When all of the broken tubes have been repaired, fill the system with water and do a hydrostatic pressure test.
If you would like more information on this process, contact Jim Devlin at Aqua Heating Systems, Inc., 267 Howes Court, Los Gatos, CA 95032, Telephone (408) 371-5457, Email. firstname.lastname@example.org