Sight glasses

An industrial sight glass is a pipeline accessory with a glass window that lets operators see the flowing fluid without opening the line. KTN Valves manufactures flanged and threaded sight glasses in Rubí (Barcelona, Spain), with single or double window, optional flow indicator wheel and a PTFE-lined execution for aggressive media.

What a sight glass is and what it is used for

A sight glass answers in one second what is happening inside the pipe: whether fluid is moving, what colour it is, whether it carries entrained air or suspended solids, and whether CIP rinse water already runs clear. A flowmeter gives the number; the sight glass gives visual evidence at a fraction of the cost. Typical positions are pump discharge, cleaning returns and upstream of strainers and control valves.

Sight glass types KTN manufactures

KTN builds two connection families and several window configurations.

• Flanged sight glasses: for medium and large bore, with ANSI or DIN flanges to match the line.
• Threaded sight glasses: BSP or NPT, for small bore, utility lines and sampling points.
• Double window: two opposed glasses, so the operator backlights one side and looks through the other. This is the choice for dark, viscous or low light transmission products.
• Single window: one viewing face, lower cost, enough for clear fluids with good ambient light.
• Sight flow indicator with wheel: a wheel turns with the stream and makes low or intermittent flow visible when a plain glass would show nothing.
• PTFE-lined: PTFE lining with DIN or ANSI flanges, for acids, chlorides and solvents that attack stainless steel.

Materials, glass and gaskets

KTN manufactures the body in stainless steel AISI 316/316L, carbon steel, PP, PVC or PTFE-lined steel. Tempered glass works up to 230 °C. The gasket usually sets the practical limit of the assembly below that figure: PTFE handles more temperature and more chemical attack than EPDM, while EPDM seals better at low pressure in water service. State fluid, concentration and temperature before the execution is fixed.

Connections and standards

KTN supplies the sight glass with BSP thread to ISO 228 and EN 10226, NPT thread to ASME B1.20.1, ANSI B16.5 class 150-300 flanges or DIN EN 1092-1 PN10-PN40 flanges. The flange face has to match the pipeline: check the flange face types and convert sizes with the DN to inches conversion table.

How to select a sight glass

Work in this order: what you need to see (flow, colour, solids, air), line connection, body material against the fluid, working temperature, compatible gasket and finally single or double window plus flow indicator wheel. Watch thermal shock: glass at 200 °C hit by cold cleaning water can crack. Ramp CIP temperatures and avoid sudden cooling across the window.

Applications and industries

KTN sight glasses run in food and beverage, pharmaceutical and cosmetics, chemical processing, water treatment and desalination, pulp and paper, marine and HVAC. Acid and hypochlorite lines take the PTFE-lined execution; sanitary circuits take the AISI 316L body with Ra 0.8 µm polished finish.

Buying sight glasses direct from the manufacturer

Buying from the factory removes the distributor margin and shortens the specification loop. KTN keeps stock of common sizes and materials for immediate despatch from Spain, manufactures special executions to drawing and issues a certificate of origin with every order. Send fluid, temperature, pressure, DN and connection type to receive a factory quotation. Distributor enquiries are welcome.

Why KTN

KTN Valves (Kara Technology News, S.L.) is a Spanish manufacturer based in Rubí, Barcelona, producing in its own facilities under an ISO 9001 quality system with Bureau Veritas inspection. Every order ships with a certificate of origin and, on request, a 3.1 material certificate. PTFE lining is applied in-house, the same technology used in the KTN 123T PTFE-lined ball valve.

Related categories

To hold particles before the pump, Y strainers. To absorb thermal expansion and vibration, expansion joints. To contain a leak at the flange gasket, safety spray shields. The full ancillary range sits in industrial accessories, and the complete catalogue in industrial valves.

Frequently asked questions

What temperature does sight glass tempered glass withstand?

The tempered glass in KTN sight glasses works up to 230 °C (446 °F). The gasket usually sets the practical limit of the assembly: PTFE takes more temperature and more chemical attack than EPDM. State both process and cleaning temperature, because CIP is often the harshest point of the cycle.

Single window or double window sight glass?

A double window places two opposed glasses so you can backlight one side and look through the other, which is what dark, viscous or low transmission products need. A single window costs less and is enough for clear fluids with good ambient light, such as water, condensate or transparent solutions.

Can a sight glass handle acids and solvents?

Yes, with the PTFE-lined execution and DIN or ANSI flanges. The lining isolates the metal body from the fluid and resists acids, chlorides and solvents that attack AISI 316. The gasket must also be PTFE. Send fluid and concentration and KTN confirms compatibility before manufacturing.

What is the flow indicator wheel for?

The wheel turns with the stream and makes low, intermittent or unstable flow visible when a plain glass shows nothing. It confirms at a glance that a pump has primed, that a dosing line is still running or that a return line has not lost flow.

Can a sight glass be installed in a vertical run?

Yes. In a vertical run with upward flow the sight glass stays full and the reading is more reliable, which helps when looking for entrained air. In horizontal runs, orient the window so it is visible from the plant walkway and leave clearance to clean the glass from outside.

Request a quotation

Send fluid, temperature, pressure, DN and connection type and KTN prepares a factory quotation with the execution fixed. Request a quotation or call +34 937 818 219.