forged and cast high pressure valves: control, stop, check, blow down, globe, gate, ball,
piston, bellows sealed, instrument
Level gauges: magnetic level gauges, glass level gauges: transparent, reflex, bicolor
Cesare Bonetti - BONT - CMI Pasquini
REFLEX GLASS LEVEL
||Left drawing shows a typical Reflex Glass
This instrument consists of a metal body, machined to have an internal chamber and one or
more front windows (on one side only of the gauge).
On each window a special high resistance plate reflex glass is fitted with sealing joint
and metal cover plates hold by bolts and nuts.
The chamber is connected to vessel with cross fittings and flanged, threaded or welded
ends. Usually, between the instrument and its connecting ends, valves are fitted to
consent shut-off piping and to disassemble the level gauge without to empty the vessel.
Drain valves can also be fitted to cross fittings device.
To avoid leakage in case of glass breakage, safety ball-check device can be provided.
Reflex level gauges working principle is based on the light refraction and reflection
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:
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.
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° towards the observer, to whom the zone will appear silver bright.
Reflex Level Gauges can be used in most of the cases and offer great advantages in terms
of: low initial cost, low operating cost, easy level reading.
Reflex Level Gauges cannot be used in certain cases (where
Transparent Level Gauges must be used) as for example:
- when the separation level between two liquids has to be read
- 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.
Our standard range of Reflex Level Gauges, starting from PN 16 up to PN 420/
ASME Class150 up
to 2500, and can be manufactured, depending on model & type, in different
materials, as ASTM A105, ASTM A350 LF2, ASTM A182 F304 / F316, Monel, Hastelloy, Incoloy,
Carpenter, Nickel, Titanium, Zirconium, Tantalum, Ebonite, PVC, Polypropropilene, PTFE
Apply to us for other materials.
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