through the orifice is regulated by a carefully contoured elongated valve needle 68 of an approximately conical but specially contoured shape having little diametral change for changes in axial length a conventional valve needle would be more foreshortened than the needle 68 and would include conical walls of approximately 30 u00b0 to 40 u00b0 off the longitudinal axis rather than the gradually tapered conical walls shown in fig2 consequently the operation of the needle 68 within the orifice 67 effects a more gradual and linear regulation of the hydraulic flow throughout the range of valve control than would a valve needle of conventional design the needle 68 merges with a stem 69 extending first through a threaded portion 70 of the valve body and then through a bore 71 in the top cap 72 a recessed o ring 73 is compressed slightly by the cap 72 affording a tight seal against the stem 69 the threaded portion 70 includes unusually fine threads for a valve application on the order of twenty four threads per inch to produce a slow rate of translation of the stem 69 for a given rotational movement approximately ten complete turns of the stem 69 are required.