Forney ClearPort observation ports are designed for installation on HRSG ducts and other hot furnaces. Forney ClearPorts provide a clear, unobstructed view of the duct burner flames as well as pressure parts downstream. Forney ClearPorts includes a butterfly-style isolation plate to restrict heat conduction towards the glass. The glass pane is suitable for high temperatures to prevent any discoloration over service life. Butterfly-style isolation plate is easy to operate with a spring-loaded side handle. When released, the spring ensures the isolation plate returns to the closed position. A cooling air inlet port is provided for the user to connect cooling air at a specified pressure and flow rate. These view ports are available in 4”, 6”, and 8” sizes and are designed to be installed on a standard #150 ASME flange.

Part Number: Single Glass

4” Diameter ClearPort P/N: VP-04.1

6” Diameter ClearPort P/N: VP-06.1

8” Diameter ClearPort P/N: VP-08.1

Part Number: Double Glass

4” Diameter ClearPort P/N: VP-04.2

6” Diameter ClearPort P/N: VP-06.2

8” Diameter ClearPort P/N: VP-08.2

Glass Pane:

Quartz Glass; Fused Silica for High Temperature


4”, 6”, 8” Schedule 40, 304 Stainless Steel

Isolation Plate:

.25” thick, 304 Stainless Steel

Rear Flange:

Pressure Class: 150, Raised Face, Sch 40, 304 Stainless steel


High-Temperature Ceramic Fiber

Temperature Range: -50 to 2,300 Degrees F.

Cooling Air: 

Flow: 6 scfm at 3” w.c. above duct pressure


4” = 68 lbs., 6” = 91 lbs., 8” = 99 lbs. (45 Kg)


All Welds AWS D1.6 or ASME B31.3

Design Temperature:

1,324 Degrees F.

Design Pressure:

69 MBAR (1.25 PSI)

Mounting Flange (by User):

ASME 4”, 6”, or 8” w/ bolt hole pattern straddling centerline

Mounting Adaptor

For installing 6” Clear Port on 4” Flange: P/N: VP-FLNG-04

Mounting Adaptor

For installing 6” Clear Port on TJ Model 15 Rectangular Flange

P/N: VP-FLNG -15

Mounting Adaptor

For installing 6” Clear Port on TJ Model 15 wall studs, flush mount


Note: Adapters are available to fit other sizes. Contact sales for more info.

CLEAR PORT User Manual

Publication 372000-89 Rev. A

  • Fused Silica Quartz Glass
    The Quartz Glass can handle temperatures up to 1,800°F and pressures up to 100 psi.
  • 304 Stainless Steel Construction
    The Forney ClearPort observation port remains clean and free of rust and corrosion, giving unsurpassed reliability.
  • Ease of Operation
    The rotating handle gives the user effortless operation and, with a spring return, ensures the isolation plate is closed when not being viewed. A must for safety in case of upset conditions occur.
  • Class 150# ANSI Flange Mounting
    Used in low to medium-pressure pipe applications, this type of connection is commonly used in mounting round observation ports. 
  • Maintenance Free
    The Butterfly design and the stainless-steel construction make the Forney ClearPort very reliable for many years.
  • Cooling Air Port
    The 1/2" NPT Cooling Air Port makes for a typical air connection.
  • Ceramic Insulation
    Forney ClearPort's ceramic insulation provides thermal breaks.
  • Dual Pane Option
    Reduces the front surface temperatures to around 140 °F