Product Overview

Spirax Sarco SG253 Set of gaskets is an original equipment sealing kit specifically designed for the SG253 double window sight glass range. Positioned on either side of each borosilicate glass window, these gaskets restore tight enclosure sealing in industrial pipelines carrying steam, condensate, compressed air, and other Group 2 fluids.

Each gasket contains a thin stainless steel support ring embedded inside reinforced exfoliated graphite. This construction preserves structural alignment within the machined body recesses of the ductile iron body under elevated temperatures and working pressures up to 25 bar g.

Key Features

• Reinforced Exfoliated Graphite: Delivers thermal stability across process temperatures up to 280 °C.
• Stainless Steel Support Ring: Built-in metallic ring prevents gasket deformation under bolt compression.
• Symmetrical Sealing Layout: Designed to sandwich both sides of each viewing window (item 3) within the cover and body recesses.
• Full Size Coverage: Dedicated sets cover SG253 nominal diameters from DN15 through DN50.
• Pressure Equipment Directive Compatibility: Operates within host equipment rated for Group 2 gases and liquids (SEP and Category 1 for DN50 gas).

Technical Specifications

Parameter	Specification
Spare Part Name	Set of gaskets (Item 4)
Host Equipment	Spirax Sarco SG253 double window sight glass
Gasket Material	Reinforced exfoliated graphite
Internal Reinforcement	Thin stainless steel support ring
Compatible Host Sizes	DN15, DN20, DN25, DN32, DN40, DN50
Maximum Design Pressure (PMA)	25 bar g @ 100 °C (PN25) / 17.2 bar g @ 35 °C (ASME 150)
Maximum Design Temperature (TMA)	280 °C @ 18 bar g (PN25) / 280 °C @ 10 bar g (ASME 150)
Minimum Allowable Temperature	-10 °C
Maximum Operating Pressure (PMO)	21 bar g (PN25 saturated steam) / 13.8 bar g (ASME 150 saturated steam)
Maximum Operating Temperature (TMO)	280 °C
Minimum Operating Temperature	0 °C (consult Spirax Sarco for lower temperatures)
Compatible Fluid Groups	Group 2 Gases and Group 2 Liquids (steam, water, compressed air)

Applications

• Scheduled gasket refurbishment during routine SG253 sight glass maintenance.
• Resealing viewing ports following window replacement due to chemical erosion from caustic alkali or hydrofluoric acid.
• Flanged steam trap discharge monitoring lines across DN15 to DN50 connections.
• Process pipelines carrying Group 2 industrial fluids requiring regular visual flow confirmation.

Maintenance and Replacement Procedure

1. Isolation: Isolate the sight glass from the piping network. Ensure all line pressure is completely vented and the body temperature has equalized to ambient levels.
2. Disassembly: Unscrew the cover bolts (item 5). Carefully detach the covers (item 2) and extract the degraded gaskets (item 4) along with the borosilicate windows (item 3).
3. Recess Cleaning: Thoroughly clean the gasket seating recesses in the body and cover to remove old graphite residues without scratching sealing faces.
4. Gasket Positioning: Install new gaskets, ensuring that one gasket (item 4) is placed on either side of each window (item 3). Reassemble the covers (item 2) and cover bolts (item 5).
5. Torque Tightening: Uniformly tighten the cover bolts according to the specified torque ratings in the table below.
6. Commissioning: Slowly open the isolation valves to permit gradual pressure and temperature stabilization. Inspect all joints for leaks.

Recommended Bolt Tightening Torques

Size	Bolt Size	Tool Across Flats	Quantity	Tightening Torque
DN15 - DN20	M10 x 30	17 A/F	8	12 N m (8.6 lbf ft)
DN25 - DN32 (Pre 08-2010)	M10 x 35	17 A/F	8	28 N m (20.6 lbf ft)
DN25 - DN32 (Post 08-2010)	M10 x 40	16 A/F	8	28 N m (20.6 lbf ft)
DN40 - DN50	M12 x 40	19 A/F	8	38 N m (28.0 lbf ft)

Safety Warning: Gaskets contain thin stainless steel support rings that present cut hazards if handled carelessly. Dispose of used gaskets in compliance with local regulations.