The U blowout preventer is designed so that hydraulic pressure opens and closes the rams and provides themeans for quick ram change-out.
Ram closing pressure closes the rams. When the bonnet bolts are removed, closing pressure opens thebonnet. After the bonnet has moved to the fully extended position, the ram is clear of the body. An eyebolt canbe installed in the top of each ram to lift it out of the preventer.
Ram opening pressure opens the rams. Following ram change-out, this pressure closes the bonnets. The rams are pulled outward, near the bonnets, before the bonnets begin moving toward the preventer body. Thisassures that the rams never obstruct the bore or interfere with the pipe in the hole. Hydraulic pressure drawsthe bonnets tightly against the preventer body and the bonnet bolts are reinstalled to hold the bonnets closed.