article 34 atmospheric sampling description of the small flow control valve unit 34 by j p stone h g eaton and f w williams review of scientific instruments vol 46 no 9 pp 1288 1299 sept 1975 which is incorporated herein as a reference in describing the operation of the valve the relative position of the o ring glands on the valve body will become more clear the valve is opened and closed by rotating the housing relative to the valve body or vice versa as shown a clockwise rotation closes the valve at which position it is shown and a counterclock movement opens the valve prior to assemble a disk 38 with the desired orifice 40 must be selected and secured in place between the o rings 26 and 36 in the cap and the upper end portion of the valve body the o rings 23 about the body are slipped over the valve body into their respective gland the valve body is then inserted into the housing and rotated until the valve body stops rotating which is the closed position the ends of the housing and valve body may be secured into a desired system such that either the housing or valve body or both may be rotated with respect to each other rotation of the valve body in a counter clockwise direction with respect to the housing will open the valve the valve is opened by rotating.