screw valve (skrovalv)

1. A stop-cock furnished with a puppet-valve opened and shut by a screw instead of by a spigot.-2. A screw with a conical point form ing a small valve, fitted to a conical seat and used for IMG:content-0385.png:[ocr errors][ocr errors][merged small] regulating flow. screw-ventilator ven"ti-la-tor), n. tilating apparatus, consist eled more on inner A venside than the outer, by which a firmer hold against withdrawal is sesured thread rectan gular thread, much used in large screws; 1, same as &, with truncated an gles; m, rounded thread; o, 9, r, special types thread. ing of a screw-wheel set in a frame or a window-pane, etc., which is caused to rotate by the pa age of a current of heated air. It exerts no mechanical force to promote the discharge of vitiated air, but it can be made to rotate in only one direction, so that it will not yield to a cold current impinging upon it from the outside, and will thus oppose its entrance. screw-well (skrö'wel), n. A hollow in the stern of some ships into which the propeller can be lifted after being detached from the shaft, when the ship is to run under canvas only. screw-wheel (skrö'hwel), n. A wheel which gears with an endle screw. screw-wire (skrö'wir), n. In shoe-manuf., a cable-twisted wire used for fastening soles to uppers. It is applied by means of a machine which, with great rapidity of action, fits the parts together, forces the pieces of wire into place, and cuts them from the coil at the proper lengths. screw-worm (skrö'wėrm), n. The larva of a blow-fly, Lucilia macellaria, which deposits its eggs or larvæ on sores on living animals. The larvæ, usually in great numbers, develop rapidly and cause serious, often fatal, results. Horses, cattle, sheep, and swine are attacked, and there are cases on record in which human beings have suffered severely, death resulting in some instances. The best remedy is a free use of pyrethrum powder, followed by carbolic acid. [Southwestern U. S.]