.~> Internal servo-motor with internal pilot valve {1}
DEFINITION
Classification: 137/219
(under the class definition) Flow control devices comprising a flow line having a contracted portion, a valve seat adjacent said contracted portion and an internal coaxial valve part comprising telescoping members, one of which is a movable needle or valve head which engages said seat.
(1) Note. These valves are commonly known as Johnson or Larner-Johnson valves, and are used principally in water conduits providing for very large flow, as in dams and hydraulic installations associated therewith.
(2) Note. In addition to one or two moving valve heads or needles the internal part of the device comprises one or more stationary members around which flow occurs. The stationary members may be merely guides for the needles or they may complete a pressure chamber arrangement in cooperation with the movable member or members, but in either case a flow channel must be formed around a stationary member and between it and the wall of the flow line; i.e., the parts of the internal device must be surrounded by flowing fluid, except for the supports or connections between the stationary member and the wall.
(3) Note. The contracted portion of the flow line constitutes a region of relatively low fluid pressure, and the usual streamlining of the needle or stationary part, or both, provides a balanced or easily controlled valve suitable for controlling large flows.
(4) Note. The inner valve element frequently comprises a closed top-shaped body having fluid pressure chambers
therein, but may comprise annular members having annular chambers therebetween, or less streamlined forms. In any form the valve head always lies in an enlarged portion of the flow line.
(5) Note. The valve may be operated (1) by fluid pressure derived either from the line or from an external source, the expansible chambers comprising (a) the telescoping valve body (b) a separate motor within the valve body or (c) a mechanical movement connected fluid pressure motor external to the line, (2) by mechanical movement or electric motor means either within or outside of the flow line; or (3) by combinations of fluid pressure operating means and nonfluid operated means. SEE OR SEARCH THIS CLASS, SUBCLASS:
455+, for line condition responsive valves of other types.
SEE OR SEARCH CLASS
251, Valves and Valve Actuation, appropriate subclasses for valves and valve actuation generally, especially
12+, for fluid actuated or retarded valves of other types, and subclasses 123+ for combined valves and restrictors in which the valve is located at the point of greatest restriction in the line.
399, Electrophotography,
237+, for liquid developer applied to a latent image within an electrophotos:graphic device.
