
Transparent Sight Glass
Polycarbonate tubes in level gauges offer a combination of durability and optical clarity, making them an excellent choice for fluid level monitoring across various applications. This tough thermoplastic is easy to handle at high temperatures and is widely used in modern manufacturing due to its outstanding properties and resistance to chemicals.
These tubes are commonly utilized in fluid level monitoring systemswhere there is a risk of breakage from impact or vibration. As an FDA-approved material, polycarbonate is widely employed in water treatment, food and beverage processing, as well as the chemical and pharmaceutical industries.

| Glass type | Polycarbonate |
|---|---|
| Outside diameter | 1/2", 5/8", 3/4", 1", 1-1/2", 2", 2-1/4", 3", 3-1/2", 4" |
| Wall thickness | Varies by O.D. (see chart below) |
| Minimum length | 1" |
| Maximum length | 145" |
| Maximum working temperature | 120°C |
| Minimum working temperature | −40°C |
| Thermal shock resistance | 60 K |
| Maximum working pressure | Consult a Douglass representative |
| Thermal expansion coefficient | 70 × 10⁻⁶ / K |
| Fragilization temperature | −175°C |
| Chemical resistance | Varies by chemical (see chart below) |
| Outside diameter | Wall thickness | Outside diameter | Wall thickness |
|---|---|---|---|
| 1/2" | 1/8" | 2" | 3/16" |
| 5/8" | 1/8" | 2-1/4" | 3/16" |
| 3/4" | 1/8" | 3" | 1/4" |
| 1" | 1/8" | 3-1/2" | 1/4" |
| 1-1/2" | 3/16" | 4" | 1/4" |
Tempered Borosilicate Level
Reflex level gauge glasses, made out of borosilicate, are a critical tool in various industrial applications, offering a simple yet effective method to visually monitor the liquid level within tanks and vessels.
These devices utilize a series of prisms embedded in the glass that reflect light differently depending on whether they are in contact with a liquid or gas. When the liquid level is present, the prisms in contact with the liquid allow light to pass through, making the liquid level appear dark against a silvery background. Conversely, in areas where no liquid is present, the prisms reflect light, making these sections appear bright.
This clear visual contrast provides an immediate and accurate indication of the fluid level, facilitating safe and efficient process managementin industries such as chemical manufacturing, petroleum refining, and power generation, where precise level measurement is crucial for operational safety and efficiency.

| THK b | RD r | 2 | 3 | 4 | 5 | 6 | 7 | 8m | 9 | 10 | 11 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 30 mm | 15 mm | 140 mm | 165 mm | 190 mm | 220 mm | 250 mm | 280 mm | 320 mm | 340 mm | 370 mm | 400 mm |
| 34 mm | 17 mm | 5-1/2" | 6-1/2" | 7-1/2" | 8-5/8" | 9-7/8" | 11" | 12-5/8" | 13-3/8" | 370 mm | 400 mm |
| Property | Specification |
|---|---|
| Hydrolytic resistance | HGB 1 (ISO 719) |
| Acid resistance | CLASS S1 (ISO 1776) |
| Alkaline resistance | CLASS A2 (ISO 695) |
| SiO₂ | Min 80% content |
| B₂O₃ | Min 13% content |
| Na₂O + K₂O | Min 4.5% content |
Tempered Borosilicate Level
High-pressure transparent level gauge glasses, serve as an indispensable tool in environments where monitoring the exact level of fluids under high pressure is critical.
Unlike their reflex counterparts, these gauges employ two pieces of flat, transparent glass mounted on opposite sides of a tank or vessel, allowing operators to observe the fluid level directly. This design is particularly advantageous in applications where it’s essential to view the characteristics of the fluid itself, such as color, clarity, and the presence of any sediments or separations.
The straightforward, yet effective, visibility provided by these gauges makes them a key component in maintaining operational safety and efficiency, ensuring precise fluid management in even the most demanding industrial settings.

| THK b | RD r | 2 | 3 | 4 | 5 | 6 | 7 | 8m | 9 | 10 | 11 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1.18" | 0.59" | 140 mm | 165 mm | 190 mm | 220 mm | 250 mm | 280 mm | 320 mm | 340 mm | 370 mm | 400 mm |
| 1.34" | 0.67" | 5-1/2" | 6-1/2" | 7-1/2" | 8-5/8" | 9-7/8" | 11" | 12-5/8" | 13-3/8" | — | — |
| Property | Specification |
|---|---|
| Hydrolytic Resistance | HGB 1 (ISO 719) |
| Acid Resistance | CLASS S1 (ISO 1776) |
| Alkaline Resistance | CLASS A2 (ISO 695) |
| SiO₂ | Minimum content 80% |
| B₂O₃ | Minimum content 13% |
| Na₂O + K₂O | Minimum content 4.5% |
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