Abstract: A coupling for high-pressure fluid achieves a long life by easily tackling wear at a connected portion due to flow of high-pressure slurry. The coupling is configured by a pipe having an inverse male screw near an end thereof; a bush being screwed to the inverse male screw; a box nut having a larger diameter hole, through which the bush can pass, on a tip end side, and a small diameter hole, through which the pipe passes, on a base end side; a block having a female screw hole that is screwed to the box nut; a washer made from soft material which is to be inserted in an accommodating space at an end portion of the fluid route; and a ring being screwed to a female screw of the female screw hole; and a polygonal hole drilled to the ring are provided, and the end portion of the pipe which passes the box nut and of which end face abuts the washer is supported by the polygonal hole.

Abstract: A clustered creature exterminating method efficiently exterminates clustered creature such as cyanobacteria in large quantity with use of a pressure which is substantially lower than that of the conventional method. The exterminating method includes the steps of: pressurizing a fluid containing a clustered creature such as cyanobacteria through a pump; suddenly lowering the pressure applied to the fluid by injecting the fluid from nozzle groups; and destroying a bonding in the clustered creature by a cavitation caused by the pressure drop. The nozzle groups may be arranged to oppose to one another to collide the injected fluids with each other, which divides the cyanobacteria into many small pieces. As a result, the cyanobacteria lose the ability to rise, and sink at the bottom of water, therefore, die because they cannot photosynthesize.