Dresser Style 31 Line Cap

Steel Pipeline End Cap for Closure, Testing, and Dead-End Capping — 2 in through 24 in

Overview

The Dresser Style 31 Line Cap is a purpose-built, gasketed steel cap used to close off sections of a pipeline during construction and pressure testing, and to permanently cap dead-end pipe stubs for future branch extensions. Constructed from standard Style 38 coupling components with a convex dished steel head welded into one end of the middle ring, the Style 31 eliminates the need for blind flanges, threaded plugs, or field-fabricated end closures on plain-end pipe.

One follower ring is welded integral to the cap body — only one gasket and one follower ring are required for installation. The cap slips over the pipe end and is tightened with standard coupling bolts, producing the same wedge-section gasket seal that makes the Style 38 coupling leak-proof under service conditions. Rated 150 PSI MAOP in all sizes.

The Style 31 is regularly supplied with a 1 in NPT vent and plug off-center (2 in and 3 in sizes receive the vent in the center of the head as standard). The vent allows air evacuation and pressure relief during initial filling and testing. Caps without vents are available on request, as are caps with locking pins for pull-out protection in pressurized dead-end service. An insulating design with insulating gasket, insulating sleeve, and pipe-end separator is available for cathodic protection applications.

Key Features

• No Pipe Threading or Welding Required: Gasketed slip-on design installs on plain-end pipe with standard coupling bolts — no special tools or pipe preparation beyond cleaning.
• Convex Dished Head: Steel convex dish welded into the end of the middle ring provides structural resistance to internal pressure loading in all sizes.
• One-Piece Welded Follower: One follower ring is factory-welded to the cap — only one field-installed follower and one gasket required. Simplifies installation and reduces parts count.
• 1 in NPT Vent Standard: Off-center vent (center on 2 in and 3 in sizes) allows air purging and pressure equalization during filling and hydrostatic testing. Caps without vents available on request.
• 150 PSI MAOP All Sizes: Rated 150 PSI Maximum Allowable Operating Pressure in all pipe sizes from 2 in through 24 in.
• Armored Gasket: Uses a Grade 27 BUNA-S armored gasket — the brass armor bites into the pipe for low-resistance electrical contact in cathodic protection systems while maintaining full sealing integrity.
• Insulating Option Available: Insulating gasket, insulating sleeve, and pipe-end separator available for full cathodic isolation at the cap.
• Lock-Pin Option Available: Caps with locking pins available for applications where the dead-end cap must resist thrust load under pressure without external anchorage or concrete blocking.

Materials of Construction

Specifications — 150 MAOP All Sizes (2 in – 24 in)

Body ring: thickness x length (in). Bolts: quantity – diameter x length. Dish head diameter (A). All dimensions in inches.

150 PSI MAOP all sizes. 2 in and 3 in sizes: vent in center of head standard. 4 in and larger: vent off-center standard. Caps without vents and caps with lock pins available on request.

Installation Instructions

1. Surface Preparation: Clean pipe end of all dirt, rust, scale, and oil. Inspect gasket seating area for imperfections.
2. Install Free Follower: Slide the free follower ring over the pipe end with the beveled face toward the pipe end.
3. Lubricate & Install Gasket: Wipe the gasket clean. Lubricate the gasket, pipe OD, and cap body flare with soapy water or non-petroleum lubricant.
4. Seat the Cap: Slide the gasket onto the pipe end and push the cap body over the gasket, seating it against the body ring flare. The convex dish head will face outward from the pipe end.
5. Install Bolts: Thread all bolts and nuts, draw up finger tight.
6. Final Torque — Cross Pattern: Tighten nuts alternately on opposite sides, drawing the follower up evenly.
   • 5/8 in Bolts — 75 Ft. Lbs.
   • 3/4 in Bolts — 90 Ft. Lbs.
7. Vent Plug: Open the NPT vent during filling and initial pressurization. Re-install the vent plug before pressure testing to rated working pressure.

? ANCHORAGE REQUIRED UNDER PRESSURE: Style 31 Line Caps must NOT be used under pressure WITHOUT ANCHORAGE OR BLOCKING sufficient to withstand the entire longitudinal thrust due to internal pressure. Failure to provide adequate anchorage will result in cap blow-off, property damage, serious injury, or death. Use lock-pin caps or concrete dead-man blocking as appropriate for your working pressure and pipe size.

Questions? Contact us at sales@watermainsupply.com or call 281.664.8000.