Small valve may play a large part during earthquake

17:00, Aug 31 2014

A small plastic valve invented in Japan could keep Porirua's residents flushing after a major earthquake.

The $400 valves are being installed in manholes in parts of the city that could suffer liquefaction in a large earthquake. If any part of the wastewater network is out, the whole system comes down.

"The moment [manholes] pop out of the ground you're done - with these valves you're down, but you're not out," Capacity Infrastructure Services engineer Des Scrimgeour said.

Four valves are put into the sides of the manholes - in a large earthquake the lid on the valves pops off, relieving the pressure and letting water in, which stops the pressure building up and "floating" up above the surface, putting them out of action.

The valves are being installed at 140 locations in the Porirua CBD and Titahi Bay, costing about $3000 per manhole. It can cost about $12,000 to fix a manhole once it has popped up.

Japanese engineering corporation Nippon Hume invented the technology and 30,000 manholes around Tokyo are now fitted with the valves. None of them popped out in the 7.3 earthquake in 2012.

Porirua is the first New Zealand city to use the technology but Capacity, working with importer Hynds NZ, is hoping other cities in the region will see its benefits.

"It's just smart business to take an old network and try to rejig it to get it up to earthquake standards of today with prime technology."


The Dominion Post