Smith-Blair · Top Bolt Coupling
Style 421 Top Bolt Two-Bolt Coupling
Epoxy-Coated Carbon Steel, 304 Stainless Hardware, Standard Sleeve
260 PSI Max Working Pressure
-20°F to +180°F Temperature
Nitrile (Buna-N) Gasket
Epoxy-Coated Carbon Steel Sleeve and Flanges
Epoxy-Coated 304 Stainless Bolts, Coated Nuts
NSF/ANSI 61 and 372
AWWA C219
2.13-27.32 in Pipe OD
9-126 lb Weight
Description
The Smith-Blair Style 421 Top Bolt coupling joins plain-end pipe with only two bolts — one on each end. A carbon steel sleeve and split flanges, finished in Flexi-Coat fusion-bonded epoxy, carry a bi-directional removable inner gasket, so one coupling covers up to 1.31 in of OD range and can join two pipes of different OD in the same nominal size.
Oversize (OS) builds at 10, 12, 16 and 24 in have one standard end and one oversized end for a wider OD spread. The 421 is the standard-sleeve Top Bolt; the Style 422 is the same coupling with a long sleeve.
Application: joining plain-end pipe of the same or different OD within one nominal size, and replacing split or damaged pipe.
Key Features
- Working pressure up to 260 PSI
- Two bolts, one per end; stab fit with no disassembly
- Removable, bi-directional inner gasket widens range up to 1.31 in and can be reinstalled
- Corrugated 304 stainless armor for better gasket seating; up to 4° deflection per end
- Certified to NSF/ANSI 61 and NSF/ANSI 372; meets applicable AWWA C219 standards
What Ships and What It Needs to Run
Included: the assembled coupling — sleeve, two split flanges, stainless armor, inner and outer gaskets, two bolts with nuts and washers — ready to stab onto the pipe.
Pipe stiffeners on HDPE and thin-wall PVC, ordered separately. Smith-Blair requires stiffeners on these pipes; ask us to quote them with the coupling.
Genuine Smith-Blair equipment, factory-new in original packaging — sold and supported by Watermain Supply, an independent industrial supplier.
12-Month Smith-Blair Warranty
Smith-Blair warrants its products to be free of defects in materials and workmanship for one year from the date of shipment by Smith-Blair. Dated proof of purchase, such as a bill of sale, is required to establish eligibility. Smith-Blair will repair or, at its option, replace a defective product; the product is returned to the factory or warehouse Smith-Blair designates.
Working Pressure
Up to 260 PSI on every size, standard and oversize. Smith-Blair's installation sheet lists a 390 PSI test pressure for the 2-12 in sizes; for a particular installation the allowable pressure also depends on pipe size and type, pipe condition, service conditions and installation workmanship.
Materials Specifications
| Sleeve |
Carbon steel (ASTM A283C, A285A or A36), Flexi-Coat fusion-bonded epoxy finish |
| Flanges |
Carbon steel (ASTM A283C, A285A or A36), split design with integral bolt-head pocket for one-wrench installation |
| Armor |
Half-hard Type 304 stainless steel, corrugated to cut friction against the gasket |
| Gasket |
Nitrile (Buna-N) per ASTM D2000, bi-directional removable inner gasket; resists water, oil, acids, alkalies and most (aliphatic) hydrocarbons |
| Bolts |
Type 304 stainless steel, Flexi-Coat fusion-bonded epoxy coated, swivel head with swivel washer |
| Nuts |
Heavy hex Type 304 stainless steel with fluoropolymer finish to prevent galling |
| Flange connector bolts |
Type 304 stainless steel, countersunk Allen head |
| Washers |
Type 304 stainless steel over a Nylon 6/6 washer for better torque transfer |
| Finish |
Flexi-Coat fusion-bonded epoxy, applied to AWWA C213 methods |
Materials subject to change by the manufacturer.
Pipe Applications
Steel, stainless steel, ductile iron, asbestos cement, PVC and copper tube sizes. HDPE and thin-wall PVC take pipe stiffeners, which Smith-Blair requires on those pipes.
Sizes
13 sizes from 2.13 to 27.32 in OD — open for the full list
| Pipe size and OD |
|---|
| 2 in - 2.13-2.95 in OD |
| 3 in - 3.10-4.20 in OD |
| 4 in - 4.46-5.60 in OD |
| 6 in - 6.56-7.60 in OD |
| 8 in - 8.54-9.85 in OD |
| 10 in - 10.64-11.83 in OD |
| 10 in OS - 10.64-12.20 in OD |
| 12 in - 12.62-13.67 in OD |
| 12 in OS - 12.62-14.40 in OD |
| 16 in - 16.00-17.85 in OD |
| 16 in OS - 16.00-19.20 in OD |
| 24 in - 24.00-26.32 in OD |
| 24 in OS - 24.00-27.32 in OD |
Choose the size in the first option; the part number shows in the last option.
Sleeve, Laying Length and Max Gap
| Nominal size |
Sleeve length |
Laying length |
Max gap |
| 2 in |
4 in |
7.50 in |
1 in |
| 3 in |
6 in |
9.50 in |
2 in |
| 4 in |
6 in |
9.75 in |
2 in |
| 6-12 in, incl. 10 and 12 in OS |
8 in |
11.75 in |
4 in |
| 16-24 in, incl. 16 and 24 in OS |
9 in |
12.63 in |
4 in |
Max gap is the largest allowed space between pipe ends.
Installation Notes
- Designed for stab fit, so no disassembly is needed: inspect the shipment, remove any banding straps, and clean the pipe where the gaskets seat.
- Measure the OD at each pipe end: where it falls in the outer gasket range, remove the inner gasket. A removed inner gasket presses back in by lining up the gasket grooves.
- Lubricate the pipe and gaskets with a soap-and-water solution that meets the water and pipe supplier's requirements, slide the coupling fully onto one pipe (the smaller pipe when reducing), then center it over both ends.
- Keep within the maximum gap between pipe ends and 4° deflection per end (see the table above).
- Tighten the single bolt on each end with a calibrated torque wrench to the torque in the instructions; do not lubricate the bolts. Recheck torque after the line is pressurized.
- Anchor the pipe: the coupling seals around it, and Smith-Blair requires proper anchoring to restrain pipe movement and prevent pull-out. Top Bolt couplings are for water service: Smith-Blair does not design or test them for gas.
From Smith-Blair Installation Instructions TI-058 (Rev 09/02/21), covering 2-12 in, in the Data Sheet tab.
Before You OrderAll Smith-Blair products are Made to Order and Non-Returnable.
Items typically shipped in 5 - 10 business days.
Anode connectors for cathodic protection, odd pipe ODs and other configurations are built to order — email sales@watermainsupply.com with the pipe OD and material.
