LEVEL GAUGES   


 

LEVEL GAUGES (Tubular / Reflex / Transparent)
 

REFLEX INDICATOR WORKING PRINCIPLE:

Reflex level gauges working principle is based on the light refraction and reflection laws.
Reflex level gauges use glasses having the face fitted towards the chamber shaped to have prismatic grooves with section angle of 90°. When in operation, the chamber is filled with liquid in the lower zone and gases or vapors in the upper zone; the liquid level is distinguished by different brightness of the glass in the liquid and in the gas/vapor zone. The reflex level gauges do not need a specific illumination: the day environmental light is enough. Only during the night an artificial light must be provided.

The different brightness in the two zones is obtained as explained below:
LIQUID ZONE

This zone appears quite dark when the gauge is in operation and lighted as above said.
Given the construction, most of the environmental light rays incident on the external face of the glass are quite perpendicular to said face and, therefore, not deviated by the glass. These rays reach the glass/liquid interface with an inclination of approx. 45°. The critical angle glass/liquid is always superior to 45°. Therefore the rays incident within the critical angle (practically the totality) are refracted within the liquid and, since the internal walls of the gauge chamber are not reflecting, the rays cannot be seen from the outside. In fact the zone will appear dark, nearly black, to the observer.

GAS/VAPOR ZONE
This zone appears almost silver bright to the observer.
As for the liquid zone, the light rays reach the glass/gas-vapor interface with an angle around 45°. Since this angle is greater than glass/gas-vapor critical angle, the rays are not refracted , but totally reflected making 90° turn, thus reaching the nearest glass/gas-vapor interface again with angle of 45°. For same reason they will be reflected and turned by 90°

TRANSPARENT INDICATOR
when the separation level between two liquids has to be read (interface),
when, besides the level indication, observation of the liquid color is required,
when the process fluid is high pressure water/steam (since in this case the glass must be protected from the chemical attack of the boiler basic water by using mica shields),
when the process fluid is such that can corrode the glass (e.g. high temperature alkaline solutions or hydrofluoric acid) since mica shields or PolyTrifluorochloroethylene shields must be used to protect the glass.

TUBULAR LEVEL GAUGES

 Tubular level gauges are simple in construction and reliable in operation for direct visual verification of level in vented or lightly pressurized tanks. The measuring tube is protected by tie rod. The level gauge are supplied with auto shutoff ball check valve to prevent leakage of process fluid in event of breakage of glass tube. Neoprene / Teflon gland packing are provided between tube and body of gauge which enables zero leakage between tube and body, additionally it facilitates removal of glass tube for cleaning without removal of gauge from tank. Tie rod construction does not provide structural rigidity. Hence we do not recommend these for nozzle centers above 1200 mm.
Options:
Scale arrangement.
Steam Jacketing.
Slotted steel tube for added glass tube protection.

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