Tuesday, October 29, 2019

Basic Control Valve Terminology: Part 2

Control Valve Terminology
Sanitary control valve
by Cashco
Reprinted with permission from Cashco.

Packing flange: A device that transfers the deforming mechanical load to the packing follower.

Packing follower: A part which transfers the deforming mechanical load to the packing from the packing flange or nut.

Packing lubricator assembly: A device for injection of lubricant/sealer into a lubricator packing box.

Pinch or clamp valve: A valve consisting of a flexible elastomeric tubular member connected to two rigid flow path ends whereby modulation and/or shut off of flow is accomplished by squeezing the flexible member into eventual tight sealing contact.

Plug: A term frequently used to refer to the closure member.

Plug valve: A rotary motion valve with a closure member that may be cylindrical or conical. Port: The flow control orifice of a control valve.

Port guiding: A valve closure member with wings or a skirt fitting into the seat ring bore.

Positioner: A position controller, which is mechanically connected to a moving part of a final control element or its actuator, and automatically adjusts its output pressure to the actuator in order to maintain a desired position that bears a predetermined relationship to the input signal. The positioner can be used to modify the action of the valve (reversing positioner), extend the stroke/controller.

Positioner, double acting: A positioner with two outputs, suited to a double acting actuator.

Positioner, single acting: A positioner with one output, suited to a spring opposed actuator.

Position switch: A position switch is a pneumatic, hydraulic or electrical device which is linked to the valve stem to detect a single, preset valve stem position.

Position transmitter: The position transmitter is a device that is mechanically connected to the valve stem or shaft and generates and transmits a pneumatic or electrical signal representing the valve position.

Post guiding: A design using guide bushing or bushings fitted into the bonnet or body to guide the plug’s post.

Control Valve Terminology
Cashco Control Valve
Pressure energized seal: A seal energized by differential pressure.

Rangeability inherent: The ratio of the largest flow coefficient (cv) to the smallest flow coefficient (cv) within which the deviation from the specified inherent flow characteristic does not exceed the stated limits.

Rated travel: The amount of movement of the valve closure member from the closed position to the rated full open position.

Seat: The area of contact between the closure component and its mating surface which establishes valve shut-off.

Seat ring: A part of the valve body assembly that provides a seating surface for the closure member and may provide part of the flow control orifice.

Shaft: The mechanical member used to support a rotary closure member.

Spring rate: The force change per unit change in length of a spring.

Stem connector: The device which connects the actuator stem to the valve stem. Stem guide: A guide bushing closely fitted to the valve stem and aligned with the seat.

Three-way valve: A valve with three end connections, used for mixing or diverting flow.

Throttling: The action of a control valve to regulate fluid flow by varying the position of the closure member. This service generates a variable pressure drop.

Transducer: A device that is actuated by power from one system and supplies power in another form to a second system.

Travel: The movement of the closure member from the closed position to an intermediate or rated full open position.

Travel indicator: A pointer and scale used to externally show the position of the closure member; typically in terms of units of opening percent of travel or degrees of rotation.

Trim: The internal components of a valve which modulate the flow of the controlled fluid.

  • Trim, anti-cavitation: A combination of control valve trim that by its geometry reduces the tendency of the controlled liquid to cavitate.
  • Trim, anti-noise: A combination of control valve trim that by its geometry reduces the noise generated by fluid flowing through the valve.
  • Trim, balanced: Control valve trim designed to minimize the net static and dynamic fluid flow forces acting on the trim.
  • Trim, reduced: Control valve trim which has a flow area smaller than the full flow area for that valve. Trim, soft seated: Valve trim with an elastomeric, plastic or other readily deformable material used
  • either in the closure component or seat ring to provide tight shutoff with minimal actuator forces.

Unbalance, dynamic: The net force/torque produced on the valve stem/shaft by fluid pressure acting on the closure member and stem/shaft at stated travel and flowing conditions.

Unbalance, static: The net force produced on the valve stem by the fluid pressure acting on the closure member and stem with the fluid at rest and with stated pressure conditions.

Valve: A device used for the control of fluid flow, consisting of a fluid retaining assembly, one or more ports between end openings and a movable closure member which opens, restricts or closes the port(s).
  • Balve, ball: A valve with a rotary motion closure member consisting of a full ball or a segmented ball.
  • Valve, diaphragm type: A valve with a flexible linear motion closure member which is moved into the
  • fluid flow passageway of the body to modify the rate of flow through the valve by the actuator.
  • Valve, floating ball: A valve with a full ball positioned within the valve that contacts either of two seat rings and is free to move toward the seat ring opposite the pressure source when in the closed position to effect tight shutoff.
  • Valve, globe: A valve with a linear motion closure member, one or more ports and a body distinguished by a globular shaped cavity around the port region.
Vena contracta: The location in a flow stream where fluid velocity is at its maximum and fluid static pressure and the cross-sectional area are at their minimum. In a control valve, the vena contracta normally occurs just downstream of the actual physical restriction.

Yoke: The structure which rigidly connects the actuator power unit to the valve.

BASIC CONTROL VALVE TERMINOLOGY: PART 1
SEE PREVIOUS POST


For more information about control valves, contact Arjay Automation. Call them at (800) 761-1749 or visit their web site at https://arjaynet.com.