Reprinted from the ACJ - August, 1994
Remember those toy rockets they used to sell before product liability insurance turned all the fun toys into foam rubber? They were clear and red plastic and you filled them halfway with water and then pumped them up with air, pulled the release and watched as your imaginary astronauts shot into space. The game was made more interesting by having to rescue the returning rocket from the neighbor's roof or the middle of a busy street, or explaining to your mother why you aimed it at your little sister.
I think of those air pressure rockets every time I see someone pressure testing a radiator. They plug all the holes, maybe they leave a little water in the core. They hit it with air pressure or pump it up with a hand pump. Then they dunk it in a tank and check for leaks. Me, I always want to look for the release knob on one of those caps or plugs. Send it flying and scare the devil out of the guy working in the next bay. Now maybe that isn't the proper attitude for a guy who writes a safety and health column, but a sense of humor can get you through trying times.
OK, let's get serious, or at least less foolish. Pressure testing a radiator can be a bit of a hazard. If you think about it, you really have a small bomb set up when a radiator is under pressure.
The danger occurs when some component of that sealed radiator gives way under the pressure. Usually it is just a small leak around the newly installed gasket, or a pin hole leak at a faulty tube-to-header repair. The danger in this situation is flying tools and dirty words from the mechanic who has to tear it apart and rework it. But it is possible that a weak tube or more likely a poorly positioned or faulty plug or cap will let go and fly some distance from the source.
With the normal testing pressure being 15 to 20 psi, this hazard is not as threatening as many others in the shop, but catch a flying plug in the teeth or eye and I'm sure you will be more careful next time. That's why cops use rubber bullets to quiet rowdy crowds. Although unlikely, excessive pressure or a particularly weak tube could result in a weak tube splitting open while your hand is resting on it, resulting in a nasty cut. So, wear your safety glasses and gloves, and keep both you and your coworkers out of the line of fire if a plug should decide to let go.
There are some other factors to keep in mind in regards to your pressure testing equipment, so that they function efficiently and safely. As we have said before, the maximum recommended test pressure for most radiators is 20 psi. Most shops that use shop air versus a hand pump to pressurize the unit have a gauge and regulator on the line. If you don't, it's a good idea. But even with a regulator/gauge, periodically check the gauge to be sure it is reading correctly. Give the gauge a tap with your finger every once in a while to make sure the needle is not sticking. Better yet, detach the gauge and pressure test it with a hand pump type testing unit to make it sure it is reading properly. Keep an eye on the air hose, making sure it doesn't show any cuts or thin spots which may fail.
Some folks use acid or base mixtures to clean the inside of a radiator by partially filling the unit, plugging the openings and sloshing it around. Two dangers exist here. First of all, the acid or caustic inside will react with the water and metal present and build up pressure in the core. Always vent the radiator often to reduce that built-up pressure. It can exceed the 20 psi limit and cause a plug to fly or a tube to fail. The second hazardous aspect of this situation is that if it fails, not only does it send a projectile flying, but the liquid that sprays out is corrosive and you will very likely be wearing it. Again, goggles, gloves, apron, face shield, etc. are necessary even if you are venting the unit periodically while cleaning.
The plugs and caps used to block off the inlet and outlet of the radiator come in a wide assortment of styles. All caps and plugs should be monitored for degradation. Some degreasing solvents and parts cleaners can cause the rubber on the plug to break down, expand or get mushy. The brass or steel portion of the test plug is very stout and it would be odd for it to fail, but watch the threads, as they may corrode away slowly, letting the wing nut or cam lock slip.
Inspect the inside of test caps to make sure they will hold tight when under pressure. Always use the right size plug or cap. Make sure the cap/plug is fully seated over/inside the hole. Tighten the plugs sufficiently, but realize that tightening the plug excessively causes the rubber to bow out and possibly contact too little of the hole edge surface, thus failing under only moderate pressure.
If you prefer nylon and rubber test plugs, try to keep them away from zinc chloride, hydrochloric (muriatic) and other acids. The nylon can get brittle when exposed to acid or acidic fumes and fail prematurely. Rinse them after use and store them where they won't be exposed to corrosive fumes. One helpful hint from a klutz like myself: don't drop the plug inside the hole. Murphy's law applies here. The plug diameter will increase for no apparent reason, making it impossible to get back out.
So now, you are wearing the proper personal protective equipment (mission control we are at t-10 seconds), gloves (t-9), goggles (t-8), and apron (t-7). You have inspected and approved the plugs (t-6), caps (t-5), air line (t-4) and gauge (t-3). You position the plugs and/or caps properly (t-2). Use the correct test pressure (t-1), and... (mission control, we have halted the countdown).
Because of your diligence, there will be no rocket shot today. The ground crew did its job. The unit is tested safely and efficiently. No injuries or flying objects. Looks like I will have to go buy one of those foam rubber rockets if I'm going to have any fun today.
The above article was written by David M. Brown, Chief Engineer of Johnson Manufacturing Company, Inc. and is published by JOHNSON with the expressed approval of the National Automotive Radiator Service Association and the Automotive Cooling Journal. Other reproduction or distribution of this information is forbidden without the written consent of JOHNSON and NARSA/ACJ. All rights reserved.
JOHNSON MANUFACTURING COMPANY
114 Lost Grove Road / PO Box 96 / Princeton, Iowa 52768-0096
Phone 563-289-5123 or Fax 563-289-3825