Spirax Sarco SGS40 Stainless Steel Double Window Sight Glass

The Spirax Sarco SGS40 is a double-window sight glass in stainless steel. It lets operators see flow, colour, clarity and carry-over in a pipeline: two borosilicate glass windows face each other in a cast stainless body, so that light passes through the fluid. It is used on condensate and feedwater lines to spot flash steam or oil, on process lines to check product, and downstream of traps to check discharge.

Technical specifications

Choosing the window protection

The data sheet is specific about glass selection. For steam, or any fluid above pH 9, it requires mica glass protectors together with the borosilicate windows. The same protectors are required above 150 C with pH above 7. Only below 150 C and below pH 7 are plain borosilicate windows sufficient. When protectors are specified the model name becomes SGS40M. Choosing correctly matters because hot alkaline liquids slowly attack plain glass.

Optional extras include a visual flow indicator flap in stainless steel to show that liquid is moving, with a spring-loaded version for vertical lines and high flow rates.

Pressure, temperature and sizes

The pressure rating depends on the connection. PN40 flanges give 40 bar g at 50 C, ASME 150 flanges 19 bar g at 38 C, and ASME 300 flanges 40 bar g at 111 C. Saturated steam service is lower: 28.3 bar g at 232 C for PN40 and 12.9 bar g at 195 C for ASME 150. Maximum operating temperature is 250 C with PTFE gaskets and 280 C with graphite gaskets, and the minimum is -10 C for the stainless version. The body is safe under full vacuum, and the cold hydraulic test pressure is 60 bar g.

Face-to-face dimensions for flanged versions follow EN 558 Series 1. At DN15 the flanged length is 130 mm and the window diameter 10 mm, rising to 350 mm and a 30 mm window at DN100; weights range from 3.5 kg to 37 kg flanged.

Specifying and fitting

State the size, connection standard, glass protection and gasket on the order. Smaller sizes (DN15 to DN25) have flanges welded onto the body; larger sizes are cast integrally. Sanitary clamp connections to ASME BPE are available from DN15 to DN50. Standards compliance is to the European Pressure Equipment Directive 2014/68/EU, and a manufacturer’s typical test report is available, with EN 10204 3.1 certification if specified at order.

Fit the sight glass where the window is visible and illuminated, protect it from knocks, and never exceed the limits of the connection. For steam, always use the mica protectors, and replace gaskets when the cover is opened.

Documents and quotation

The official Spirax Sarco technical information sheet TI-P130-28 is attached to this page; it covers the SGC40 and SGS40 and holds the materials, pressure-temperature limits, dimensions and glass selection guidance used above. Seven Star LLC is an independent supplier in Muscat. To request a quotation for SGS40, send the model, size, end connection, any certification you need under EN 10204 and the quantity so the request can be matched to the data sheet before we reply.

We recommend confirming the exact size, thread standard and material with the attached document before placing an order. Related items: product category.