In June this year US Bureau of Reclamation (USBR) completed the removal of 12 needle valves at the Hoover dam and replaced them with eight 68in and four 90in jet flow valves.

The fixed price contract was completed by J R Jacks Construction Corporation of Las Vegas, Nevada, US. The contractor tested four gates on the Arizona side in January 1998, and on June 11 all the gates were opened for 30min.

The replacement of needle valves, with safer jet flow gates at USBR facilities, was prompted by failures of the needle valves at two dams, which killed five operating personnel.

The first failure was in January 1984 at USBR’s Bartlett dam, in Arizona. The second, also in 1984, was at a dam owned by the utility company, Utah Power and Light in Idaho.

Investigations of the accidents established that the failures were caused by operator error.

Needle valves, developed in about 1910 by the USBR, operate using reservoir water pressure and require extensive maintenance and trained operators. The investigation of the Bartlett valve failure indicated that a pressure surge caused by a rapid closing of the valve ruptured the valve body.

The replacement of the needle valves at the Hoover dam was the last contract in the USBR’s $2.5M five-year programme to replace needle valves with jet flow gates in dams owned by the federal agency.