Download datasheet Datasheet
Product video Product video
for welding on pipelines
Tank sight glass PN 16 | PN 25 | PN 40
Non binding • Usually a response within 24 hours
The circular Type 391 sight glass fitting is a tank sight glass with a pipe attachment for the visual monitoring of processes in media-carrying pipelines and sharply curved tanks.
The fitting is welded onto the pipe connection and enables reliable observation of liquid or gaseous media as well as internal process conditions.
The circular Type 391 sight glass fitting is manufactured from corrosion-resistant stainless steel 1.4571 as standard. The base flange with pipe attachment allows the fitting to be integrated into pipelines or installed on sharply curved tanks.
A transparent borosilicate glass plate according to DIN 7080 is used as the viewing window. The glass offers high chemical resistance. Alternative glass materials are available according to customer requirements.
More than 50 sealing materials are available for sealing the sight glass. Depending on the medium, pressure, temperature and chemical process requirements, options include fibre gaskets, PTFE (Teflon®), NBR, novaphit® MST-XP and KlingerSil® C4400.
For increased thermal requirements or exposure to steam, the sight glass can be equipped with a suitably adapted mica protection disc. For aggressive chemicals and caustic solutions, the borosilicate glass can be additionally protected against chemical exposure by an FEP protective screen or FEP coating. A Halar® coating is also available as an alternative.
Type 391 can optionally be equipped with an SGW sight glass wiper featuring a PTFE, silicone or EPDM wiper blade. For poorly illuminated tanks and pipelines, an LED light for Ex and non-Ex areas can be fitted to improve visibility.
Custom designs are also available for non-standard installation conditions and process requirements.
The circular tank sight glass with pipe attachment is used when processes inside media-carrying pipelines or sharply curved tanks must be observed and monitored visually.
Typical applications can be found in industrial plant and equipment construction. Type 391 is also used in the chemical industry and process engineering.
| DN | 100 | 125 | 150 | 200⁴ | 300⁵ | 350⁵ |
|---|---|---|---|---|---|---|
| Diameter [mm] (PN 16) | 220 | 250 | 285 | 340⁴ | 460⁵ | 520⁵ |
| Weight [kg]² (PN 16) | 10.5 | 14.5 | 18.6 | 28.2 | 55.7 | 78 |
| Diameter [mm] (PN 25/40) | 235 | 270 | 300 | 375 | - | - |
| Weight [kg]³ (PN 25/40) | 14.8 | 21.1 | 27.5 | 52.6 | - | - |
| Inner diameter [mm] | 107 | 132 | 160 | 207 | 310 | 340 |
| Length [mm] (Standard) | 70 | 70 | 70 | 70 | 70 | 70 |
| s [mm] | 3.6 | 4 | 4.5 | 6.3 | 7.1 | 8 |
| A [mm] | 114.3 | 139.7 | 168.3 | 219.1 | 232.9 | 355.6 |
| ² If applicable smaller or larger, depending on size of D and L | ||||||
Type 391 is designed for the visual monitoring of processes in pipelines carrying media and in tanks with high curvature. The fitting allows media and process conditions to be observed without the need to open the system or interrupt the ongoing process.
The sight glass fitting features a base flange with a pipe connection and is welded onto the pipeline or the designated pipe connection. This creates a stable and permanently leak-tight connection to the system.
Type 391 is available in nominal sizes DN 100, DN 125, DN 150, DN 200, DN 300, and DN 350. Depending on the nominal size and configuration, nominal pressure ratings of PN 16, PN 25, and PN 40 are available.
No, the permissible operating pressure depends on the nominal size and design. A maximum of 40 bar (gauge) is possible. According to the dimension table, the operating pressure is limited to a maximum of 10 bar (gauge) for DN 200, and to a maximum of 6 bar (gauge) for DN 300 and DN 350. This limit is primarily determined by the feasible glass thickness. For the specific design configuration, factors such as temperature, the medium, and the materials used for the glass and gaskets must also be taken into account.
The Type 391 is available for temperatures ranging from 80 to 400°C. The actual permissible operating temperature depends on the selected glass, gasket, and protective shield configuration, as well as the operating pressure and medium.
The flanges are manufactured as standard from 1.4571 (316Ti) stainless steel. Borosilicate glass compliant with DIN 7080 or a custom glass solution is used for the viewing window. More than 50 different sealing materials are available for the seal.
Available options include the SGW sight glass wiper, LED lights for hazardous and non-hazardous areas, mica protective shields, and FEP or Halar® coatings. Custom designs also allow for adaptation to specific installation and process conditions.
