Sight Glass Shielding Options
When shields are required, what materials to specify, and how to choose between transparent gages, reflex gages, and magnetic level indicators for your service conditions.
When Are Shields Required?
Sight glass shields are protective covers that contain the initial release if the glass fails. They are required — or strongly recommended — in the following situations:
Pressure above 50 PSIG
OSHA 1910.217 and most insurance carriers require shields
Temperature above 212°F
Steam and hot water service — scalding risk on failure
Hazardous or toxic fluids
Any fluid that poses a health risk on release
Corrosive fluids
Acid, caustic, or solvent service
Flammable fluids
Hydrocarbon service — fire risk on glass failure
High-traffic areas
Anywhere personnel regularly pass near the gage
Shield Material Selection
| Material | Max Temp | Chemical Resistance | Notes |
|---|---|---|---|
| Polycarbonate | 250°F / 121°C | Good — most acids, water, oils | Most common; excellent impact resistance |
| Acrylic (PMMA) | 180°F / 82°C | Good — water, dilute acids | Lower cost; not for ketones or esters |
| Borosilicate glass | 450°F / 232°C | Excellent — most chemicals | For high-temp service; fragile |
| Stainless steel (opaque) | 800°F / 427°C | Excellent | No visibility — for extreme service only |
Gage Type Selection
Transparent Gage
Two flat glass windows with the process fluid visible between them. Best for colored fluids, interface detection, and applications where the fluid color is meaningful. Requires shields in hazardous service.
Best for: Colored fluids, interface level, general service
Reflex Gage
A single glass with prismatic grooves. Liquid appears dark; vapor appears bright — high contrast makes reading easy. Not suitable for interface detection. Requires shields in hazardous service.
Best for: Clear fluids, steam/water interface, easy reading
Magnetic Level Indicator (MLI)
No glass at all. A float with a permanent magnet rides inside a non-magnetic chamber; external magnetic flags flip to indicate level. Zero glass failure risk. Suitable for any pressure, temperature, or fluid.
Best for: Hazardous, high-pressure, high-temperature, corrosive service
Need help selecting a level gage?
Tell us your fluid, pressure, temperature, and service conditions — we'll recommend the right gage type and shield configuration.
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