Why do they crack?

I just was thinking, why do the clear top WB's crack so often? I cannot see any reason why they would. Manufacturing flaws, too much pump pressure? Why do they crack?

Alota plexi is quite brittel. And if the plexi is to thin, and the pressure put apon it is not equal accross the entire top its only a matter of time before the stuff cracks. Also the barbs we use most often use pipe taps that are tappered, this puts a lot of pressure on the plexi rite around the threads of the barbs.

Clear tops cracks...

Same thing happens to PolyCarbonate(PC, makrolon, lexan).
PC is really, really shock resistant, but it will crack under constant (static) pressure that makes it bend. You can put it under pressure, i.e. a screw holding it down, but you have to have support from the material UNDER the PC sheet and make sure it isn't bending.
I don't know the exact physics behind that phenomena.

Even worse is that some chemicals can cause microfractures in the plastic, so beware of what you clean the plastic with! those fractures will develop even faster under pressure.

paxmax has got it down for the most part.
when you have those hard barbs pushing out on a NPT connection, it gives it LOTS of stress. thats why most people are using polypro barbs with poly now. It reduces it a lot. Also, when tapping the plastic, you can get micro cracks thatll develop into large cracks over time if you have the constant pressure.


Jon

So I just purchased a Maze3 with poly Top and I'm expecting it to crack sometimes later on down the road?

lame...

nah, probably not, I guess they have some stuff going on to prevent those from cracking, Lately theres been tons less maze 3 blocks cracking...

i used nylon barbs on my polycarb top and it hasnt cracked (been a month n a half) and im pretty sure i did a crap job in tapping it