schedule 40 4" Pipe has an operating pressure of 133 psi and a burst of 710. schedule 80 has 194 psi operating and burst of 1110. at its maximum operating temperature of 140, reduce strength by 20%
insulating capability is relative. While true that pvc is not as good a conductor of heat as aluminum, it also holds heat longer than aluminum. As soon as there is no more heat added, heat will dissipate- and aluminum with dissipate faster than pvc.
there's a break even point- the black aluminum tube will heat faster, but cool faster. the pvc will heat slower, but cool slower. there's pretty much a maximum amount of heat that can be gained by the water, based on a variety of factors, including cooling of the tube by simply driving. I Would probably take an educated guess to say that if driving and being out in the sun, the pvc pipe will not be more than a few hours from reaching the same peak temp as the aluminum tube. I would also reasonably guess that as your source of heat disappears, the pvc will maintain heat longer than the aluminum. 4" pvc has an approximate r value of .30- give or take, a little. It isn't substantial in this regard.
there's a few annoyances with this type of system, material science aside. you have to be parked relatively level, or forward, back, whichever to aid in the water reaching the sprayer. generally, ovalized tubes that are wider than they are taller are more sensitive. depending on the angle, you may leave about a gallon behind. my calculus is a little rusty, but it can be calculated out. that or just park differently.
my biggest gripe with any of these roof mounted systems is that you are adding about 8.34 lbs per gallon (roughly 50 lbs) of water weight + weight of system on to the roof!
the effects on vehicle dynamics is huge! I don't even know where to begin to calculate the increase of the center of gravity,and increased roll. even worse, it appears the recommended mounting area is toward the outer edge of the vehicle on one side- making the vehicle consistently unbalanced.
if keeping water up high was a good idea, rv's and campers would be putting the water supply on top, and not at the lowest point, and in the center.
if you've ever driven offroad and was off camber, teetering on toppling over- imagine the same situation but with 50 lbs off the side
for some reference, the mitsubishi evolution, had a version that uses an aluminum roof. Keeping the same dimensions, the center of gravity was reduced by 3mm, and reduction in roll by 1.3%. To achieve the same results with the standard steel roof, they would have to chop the roof line by 70mm.
So how much weight are we talking about for this compact sports car? 19lbs for the aluminum roof. 28 lbs for the steel, on a vehicle which is low slug.
imagine putting it on a lifted SUV with an already high center of gravity.
