Line blind valves have been in use since the 1950's and there are several varieties available that fall into one of two categories, line spreading or non line-spreading. Line blind valves that spread the piping system to release the spectacle blind typically require that a series of bolts be turned, either with a wrench or bar, to jack the seal surfaces apart. This style of valve can be labour intensive and cause significant unwanted stresses in the piping system.
Non line-spreading valves are available in two main designs, the first uses a cammed or threaded pinion gear to separate the sealing surfaces and allow repositioning of the spectacle blind. This design requires many moving parts and is typically operated by a handwheel. The second design uses a gate that passes through resilient seats to either allow full flow or activate the line blind. This design is subject to wear of the sliding seals and cannot withstand high pressures or temperatures.
There are several line blinds known in the prior art, but each has disadvantages over the present invention. Some of the prior art devices have the disadvantage of requiring line spreading or use face seals. Others use hand wheel actuation, which increases the weight, cost, and labour requirement for the blind valve. Still other prior art blind valves are large, have many moving parts, are vulnerable to exposure to the elements, and are expensive to actuate.