How are the directions of threads specified?
Thread Content
In production, how is it determined which way the threads should face? Why do some valves need to be turned clockwise to open?
This post was last edited by VALVEDESIGN on 2009-8-29 at 16:33. (1) The direction of threads is defined as follows: right-handed threads are considered positive, while left-handed threads are negative. (2) Generally, when turning the knob or handle of a valve clockwise, it should close; I’ve never heard of a valve that opens when turned clockwise
The direction of a thread is determined by the way it is screwed in: clockwise is considered positive, while counterclockwise is negative. Under special circumstances, the valve is opened clockwise; it is designed differently from the usual practice to prevent accidental operation.
The pressure relief valves on oxygen and acetylene cylinders commonly used in construction are turned clockwise to close (to prevent gas from escaping) and counterclockwise to open (to allow gas to flow).
The threads on the air outlet of bottle valves come in left-hand and right-hand types; left-hand threads are used for cylinders containing flammable gases, while right-hand threads are used for cylinders containing non-flammable gases.