I was told that back in the day this operator used Nitrogen to blow out the system and they were cleaning out in the back of a ready mix truck. The SPONGE went into the ready mix tub out the front of the tub and than blasted into the cab of the truck.

Has that made u-tube yet? Yes,there are really some stories out there.I knew an operator that blew out system one night on a river in Atlanta,brought out police,fire dept and anyone else it woke up.They say it sounded like a bomb,sponge never recovered.

met an operator in calif. last week that still uses nitrogen gas. By the way...its used because its portable and is pressurized between 2-3000 psi...as compared with 200 psi air compressors. I guess they just throw safety out the window.

The somewhat intelligent folks use a regulator between the bottle and the line to be blown out. Many small pumps have nitrogen accumulators on the discharge as a surge dampener [very effective] so the nitrogen is, for them, a natural.

 The sponge must have froze into a brick because of the nitrogen?

Liquid Nitrogen or Nitrogen?

i was on a job one time pumping a slab and another company was pumping block and i saw them blow out and watched their sponge go through a window on the building

both liquid and gaseous nitrogen could freeze...but liquid nitrogen, once it hits ambient temps, will turn to gas and expand exponentially. If a sponge got frozen it would not be like a brick...it would become brittle and break up as it pushes against the concrete.