Battery-operated pumping unit for gas analysis

1,119,434. Valves. MINE SAFETY APPLIANCES CO. 17 March, 1966 [2 April, 1965], No. 11771/66. Heading F2V. [Also in Division G1] A valve comprises a body 42 having a chamber 41 therein with an inlet 40 and outlet 43, a valve stem 44 screwed into the body 42 and having an inner end for throttling the inlet 40, the stem being provided with a passage 46 having one end open to the atmosphere and its other end in communication with the chamber 41, and thus the outlet 43, by way of openings 47. A hollow inner stem 48 is screwed into the stem 44 and this has an inner end co-operating with a valve seat 49 for throttling the entry of air from the atmosphere via the passage 46. The valve is intended for use with gas analysis apparatus in which a battery-driven pump is connected to the outlet 43 to draw a restricted gas sample flow through an analyser connected to the inlet 40, and in which air is admitted via the hollow valve stems to the gas flow so that the pump is working with a full flow, thus preventing undue drain on the battery which would occur if the restricted flow through the analyser was the only gas flow through the pump. An alternative valve construction is also described in which the inner valve stem 48 is omitted and one opening 47 to the atmosphere is provided, this being partially obturated by a portion of the valve body, the opening being progressively uncovered as the valve stem is screwed down to throttle the inlet 40.