Re: CAC- Charge Air Cooler leaking
Reply #16 –
First of all let me say this, John. I salute you on your repair, I think it's a fine example of problem solving using available technology. It obviously worked for you and may work for others as well.
As Pierce says, these failures are most likely due to stress cracking. I suspect the cracking is caused by the cooler expanding and contracting due to heat and pressure cycling. Aluminum, unlike wood and some composites has a finite number of bending cycles it can go through. Exceed this and it will crack. Restrain it from bending and it won't.
As far as the calculations go, using 28psi as a max pressure seems valid, I think most Banks equipped engines will develop this but dropping it to 20 psi still yields some pretty extreme pressure on the device. While it's true that it's open at both ends, one end has a pump hooked to it and the other end is restricted by the mostly closed valves of the engine and pressure in a closed system is distributed evenly. Without knowing the total surface area of the cooling chambers it's impossible to calculate exactly what the total force is but the collector and exit chambers will be subject to some extreme pressures due to the large surface area of these chambers. I suspect but don't know that the cracks are typically in this area rather than the cooling tubes.
I'm always amazed at the way it adds up. That's also the reason welded aluminum marine fuel tanks are pressure tested at 3 psi or less. Even with welded baffles inside they are bulging like sausages at 3 lbs. That's because a 2' X 2' X 8' tank has 31,104 LBS of force distributed inside at a pressure of 3 psi. That's how 100 psi exerted on six one square foot or less patches will support a 30000 lb coach down the road and 40 psi on these same patches will lift it.
Enough from me on this, I'm sure most folks find this both boring and irrelevant. I'm fascinated by it but then my heroes are all engineers.
Topic: CAC- Charge Air Cooler leaking