Kawaki FS-II Sight Flow Indicator With Flapper – ANSI 150LB Raised Face

Overview

The Kawaki FS-II Sight Flow Indicator with Flapper is a visual flow-verification device that lets operators confirm the presence, direction, and relative rate of liquid or gas flow in a pipeline at a glance, using a rotating flapper vane visible through a sight-glass window. It is used by process engineers and operators across Oman and the GCC on piping systems in refineries, chemical plants, and utility installations where continuous visual confirmation of flow is a practical, low-cost complement to instrumented flow measurement.

The “II” designation in the FS-II identifies the flapper-type configuration within Kawaki’s FS sight-flow indicator range, distinguishing it from drip-type or bull’s-eye variants that show flow through droplet formation or window fogging rather than a moving mechanical vane.

Operating Principle

As fluid passes through the indicator body, it deflects an internal flapper vane, which is directly visible through a transparent sight-glass window mounted in the housing. The degree and speed of flapper movement gives operators an immediate visual indication of flow presence and relative velocity, and on FS-II variants, the window can be marked with outline flow-rate scale graduations for a rough visual read of flow magnitude, not just flow/no-flow status.

Engineering Design of the Kawaki FS-II

This unit is supplied to ANSI 150LB raised-face flange configuration, with a body available in cast iron (FC250), high-tensile cast iron (FC450), bronze (CAC406), carbon steel (SS400), or stainless steel (SUS304/SUS316) depending on process compatibility requirements. The sight-glass window uses phosphor bronze (C2801P) or stainless steel (SUS304/SUS316) framing with a transparent viewing glass. The indicator is rated to withstand 1.0 MPa pressure at temperatures up to 80°C under standard specifications, and is available in bore sizes from 3/8B to 6B in flange configuration (special order up to 12B) or 3/8B to 2B in screw-connection configuration.

Key Features

• Flapper-type visual flow indication through sight-glass window
• ANSI 150LB raised-face flange connection
• Body materials: FC250, FC450, CAC406, SS400, SUS304, SUS316
• Sight-glass frame: C2801P (phosphor bronze), SUS304, or SUS316
• Pressure rating 1.0 MPa, temperature to 80°C
• Size range 3/8B-6B (flange), 3/8B-2B (screw), special order to 12B
• Optional flow-rate scale graduations on the sight window

Industrial Applications

Across Muscat, Sohar, and Salalah, the Kawaki FS-II is used in refineries, petrochemical plants, and utility piping systems as a low-maintenance, no-power visual check point for confirming flow at pump discharges, drain lines, sample points, and process transfer lines. Its mechanical simplicity makes it a reliable backup indicator alongside instrumented flow meters, giving operators an immediate visual cross-check during rounds or troubleshooting.

The stainless-steel body and window variants are also specified for corrosive or hygienic process lines in chemical and water-treatment facilities across the region, where material compatibility with the process fluid is the primary selection criterion.

Technical Specifications

Selecting the Right Sight Flow Indicator

A sight flow indicator must suit the line it is installed in as well as the fluid it shows. Before ordering, confirm the nominal pipe size, the ANSI 150LB raised-face flange rating, and the body and window materials against the process fluid, the design pressure and the design temperature. A flapper design like the Kawaki FS-II is a good choice when operators need to see movement clearly, for example on clear liquids where a bull’s-eye type would show little. For very viscous, dirty or highly pulsating services, discuss the application first, because the flapper may stick or wear faster.

Installation Guidelines

• Install the indicator with the flow arrow in the direction of flow. Check the manufacturer’s instructions on permitted orientation, because a flapper that relies on gravity to return needs to be mounted the right way.
• Place it where operators can see the window easily from the walkway or platform, with enough light to read it.
• Use new gaskets suitable for the service and tighten flange bolts evenly in a cross pattern. Uneven bolting can stress the body and the window.
• Flush the line before fitting so that debris does not scratch the glass or jam the flapper.

Maintenance and Inspection

Include the indicator in routine operator rounds. Look for leaks at the window seals and flanges, discolouration or deposits on the glass, and a flapper that sticks or moves irregularly. If the window becomes hard to see through, isolate and drain the line before removing the cover for cleaning. Replace gaskets whenever the window assembly is disturbed. Any cracked or chipped glass should be replaced straight away rather than left in service, especially on hazardous or hot fluids.

Where It Fits in Oman and GCC Plants

Sight flow indicators are commonly installed on pump discharge lines, cooling water returns, chemical injection lines, lube oil systems and drain lines in refineries, petrochemical plants and utilities across the region. They give a simple local check that complements transmitters in the control room and is useful during start-up and troubleshooting.

Supply from Seven Star LLC

Seven Star LLC supplies Kawaki sight flow indicators and other line instruments to plants and contractors in Oman and the GCC. Share your line size, flange rating and fluid details, and we will help confirm the right configuration.

Request a Quote for Kawaki FS-II Sight Flow Indicator With Flapper – ANSI 150LB Raised Face

Seven Star LLC supplies the Kawaki FS-II sight flow indicator to process industries across Oman and the GCC. Contact our engineering team for a formal quotation and material selection support for your pipeline application.

Browse the full Kawaki range or see more Flow Indicators & Switch products supplied by Seven Star LLC in Oman and the GCC.