A–B–C–D–E–F–G–H–I–J–K–L–M–N–O–P–Q–R–S–T–U–V–W–X–Y
Laminar Flow
The flow of a viscous fluid in which the fluid moves in parallel layers with a fixed velocity gradient from the centerline to the containing walls of the conduit. Sometimes referred to as Streamline Flow.
Leak Rate
Rate at which a fluid (liquid or gas) passes a seal or barrier.
Lifting Lugs
Lugs provided on equipment for lifting and positioning. Also termed Lifting Eyes.
Limit Switch
Switches which are actuated at preset values by the movement of the valve. Normally fully open or closed positions, but can be set at intermediate points of travel. Types include mechanical, magnetic (reed) and proximity.
Line
A pipe, tube or hose for conducting fluids.
Linear Actuator
A linear actuator is a device that develops force and motion, from an available energy source, in a linear manner, as opposed to rotationally like an electric motor.
Linear Flow Characteristic
An inherent flow characteristic which can be represented ideally by a straight line on a rectangular plot of flow versus per cent rated travel. Therefore equal increments of travel yield equal increments of flow at a constant pressure drop.
Linebreak System
A system incorporating a pressure transmitter to sense the rate of pressure drop in a pipeline. When the rate of pressure drop falls outside a preset value, the control system will close the valve. Can be electrical or mechanical.
Lip Seal
A circular seal ring of U shaped cross section encompassing a spring element which provides resiliency and ensures a seal at the inner and outer lips of the U.
Liquid Penetrant Test
An NDE method of detecting the presence of discontinuities that are open to the surface such as cracks, seams, laps, cold shuts, laminations, lack of fusion in welds, castings or forgings, through the use of a special coloured dye liquid. Techniques and procedures are covered in ASME V, Art. 6 and ASTM E165.
Locking device
A device that can be fitted to either lever or gear operated valves to allow for the valve to be locked in either the fully open or closed position.
Lube Seats
Seats which are equipped with a lubricant injecting system.
Lubricant
Any substance interposed between two surfaces for the purpose of reducing the friction or wear between them.
Lubricator
A device that adds controlled amounts of lubricant to a fluid power system.
LVDT (Linear Variable Differential Transformer)
A device used in modulating service to provide position feedback of the valve position. Provides an electrical output proportional to valve position.