Straining valves

A straining valve comprising:

• a body having an inlet, an outlet, a chamber for accommodating a valve plug, said chamber being between and communicating with said inlet and outlet, and a flush port between said inlet and outlet and communicating with said chamber,
• a valve plug seated in said chamber and having an axis of rotation, said plug having a plug flow passage therethrough directed transverse of said axis, said plug flow passage having first and second openings at the ends of said passage, said openings respectively aligning with said inlet and outlet for permitting fluid to flow from inlet to outlet when said plug is rotated to a first, valve-open position, and said plug passage having a third opening therefrom through the wall of said plug between said first and second openings, said first opening being large enough to communicate with both said inlet and said flush port when said plug is rotated to a second self-cleaning position, in which position said third opening communicates with said inlet, and
• a first filter area positioned in said first opening, and a second filter area positioned in said third opening,
• wherein said first filter area filters fluid passing from inlet to outlet in said first, valve-open position, and in said second position part of the fluid from said inlet flows across said first filter area and then out said flush port, to clean said first filter area, and part of the fluid from said inlet passes through said second filter area and is filtered as it passes therethrough, then passes into said plug flow passage, and finally passes out through said first filter area and flush port, to backflush and thereby to further clean the first filter area.