Palito
Husqvarna
AA Class
I had a friend straighten a pipe with water pressure, capped one end and filled it with water making sure no air is trapped in it. Capped the other end and attached a high pressure hose to a laboratory test hand pump. Critical thing is bleeding out any air. Then simply pumping it up slowly and watching as the pipe straightens out before your eyes. It takes as much as 800-1,000 psi but is safer than heating an air pressurized pipe. Water is not compressible so if it develops a leak or splits a seem open the pressure is released immediately, no projectiles or catastrophic damage to the pipe. Absolutely critical not to have air in the system. This works best to restore the shape of a pipe and large caved in dents, not so good on the little stone dents. The pump my friend used was about 60 years old, don't know if they still make them. Also it only took about 3 or 4 pumps on the hand lever to achieve those pressures. If it takes more the a few pumps it means there is air in the system that needs to be bled out. I was totally amazed by the process.