The PRVs are part of the original turbine equipment in the dam's powerplant. When the water flow to the turbines must be stopped quickly, the PRV's divert the water around the turbine and directly into the river. This reduces the pressure rise that would otherwise occur in the penstock - the large pipes that carry the water from Lake Mead to the turbines.

Precision Machine & Supply, Inc., will disassemble, remove, rebuild and re-install two PRV's between October 2006 and spring 2007. The contract also provides options for the overhaul of an additional five PRVs in future years.

"The repair and overhaul of the PRVs, will help restore the valves to original operating performance, and with ongoing minor maintenance, should enable them function reliably for more than 30 years before there is a need for additional major repairs," said Acting Reclamation Commissioner Bill Rinne.

He added the overall goal of maintaining pressure relief valves is to protect the life of the penstocks.

The work is not expected to affect power generation or water delivery operations, and it will not interrupt visitor operations or tours.

The rehabilitation work, like all operations and maintenance work at Hoover Dam, is funded by the dam's power customers.