Double Window Sight Glass

A short flanged spool with a transparent window on each side, fitted into the line so you can see the fluid inside it. With windows opposite one another you can backlight the flow — a lamp at one window, your eye at the other — which makes clear and pale fluids visible when a single window would show almost nothing. It tells you whether the line is flowing, whether it is running full, and whether the fluid has changed colour or picked up solids.

Body and flanges in Carbon Steel (WCB), 304 or 316 stainless, CF8M, duplex, Hastelloy, or PTFE-lined where the media is corrosive. Windows in borosilicate or toughened glass selected for the pressure and thermal duty, with PTFE or elastomer gaskets chosen for the media.

DN 25 to DN 200 (1″–8″) at ANSI 150# and ANSI 300#, with face-to-face and flange drilling to the applicable standard so the unit drops into a flanged run without re-piping. MVS is ISO 9001:2015 certified.

Fit it in a straight run away from immediate elbows so the flow is representative, where it can actually be seen, and out of positions exposed to mechanical knocks — pump discharge lines, downstream of a strainer, and on dosing and transfer lines are the usual spots. Keep the windows clean, inspect the glass at each shutdown for etching or crazing, and renew the gaskets whenever the cover is opened. What breaks sight glasses is thermal shock and uneven bolt loading, not steady pressure.

MVS manufactures at its own works — since 1978, ISO 9001:2015 certified — and exports across several continents. The minimum order quantity is 20 pieces. Hastelloy and duplex bodies, PTFE-lined construction and non-standard flange drilling are built to order. For fully corrosive service see the PTFE Lined Sight Flow Indicator.