| 摘要 |
<p>891,624. Valves. DOWTY MINING EQUIPMENT Ltd. Dec. 29, 1958 [Jan. 2, 1958], No. 220/58. Class 135. A breather valve, e.g. for an hydraulic pitprop comprises a spring-loaded closure member 12 normally held in open position by the weight of a ball 8 which acts on the member 12 through a plunger 11. The ball 8 is located in a cupshaped housing 5 fixed to or integral with the cover-plate 3 of the hydraulic liquid reservoir 1. When the ball closure member 12 is spaced from its annular seat 18 air from the reservoir 1 may pass through a bore 16 in the plunger 11 or past the sides of said plunger into the housing 5 which has filter-covered air vents 19. The pit-prop cap has an air vent 30. The ball 8 normally seats on a conical surface 7 but on tilting of the prop it rides up the convex and concave surfaces 5B, 5A to allow the spring 13 to close the ball valve 12 against the seat 18, so preventing escape of hydraulic fluid from the reservoir 1. The surfaces 5A, 5B may be rectilinear. When the prop is horizontal the ball is prevented by the surfaces 5A, 5B from re-opening the valve even if accidental mechanical shocks are imparted to the prop.</p> |
