20" Single-Bolt Flush Manhole (Model #SB540-20A) - Painted Steel

The Model SB540-20A features a high-strength central bolt mechanism engineered to exert massive, uniform compression across the entire sealing perimeter with minimal effort. By using a single recessed bolt instead of a multi-bolt configuration, crew members can achieve rapid sealing and opening times during routine operations. When fully tightened, the bolt assembly sits below the deck level, ensuring a completely clear, smooth surface for high-traffic environments, cargo shifting, and vehicle wheels.

Intended Use Cases:

• High-Load Deck Access: Ideal for placement in direct paths of heavy deck machinery, cargo storage zones, and vehicle thoroughfares where a completely flat profile is mandatory.
• Tank Isolation & Safety Boundaries: Provides dependable, heavy-duty watertight containment for fuel oil storage, ballast tanks, and under-deck dry voids.
• Large-Clearance Entry: The expanded 20-inch opening offers generous clearance for personnel wearing bulky safety gear or tools to pass through during structural inspections and clean-outs.

Primary Industries & Vessel Types:

• Commercial Workboats & Tugboats: Perfect for high-traffic main decks on harbor tugs, push boats, and offshore utility vessels.
• Inland & Ocean Barges: Sized right for deck flats on liquid cargo carriers, aggregate barges, and crane platforms.
• Marine Infrastructure & Floating Terminals: Suitable for heavy-duty traffic areas on floating docks, fuel transfer piers, and municipal marine structures.

• Flush Deck Surface: Engineered for a 0" profile height, eliminating tire-damaging or tripping hazards while allowing completely unobstructed movement of forklifts, vehicles, and cargo.
• Single-Bolt High-Torque Mechanism: Simplifies closure down to a single central 7/8" - 9 x 3-1/2" heavy-duty bolt, allowing rapid securing and opening while generating maximum, balanced clamping pressure across the sealing perimeter.
• Heavy-Duty Structural Steel Plate: Crafted with thick structural steel to resist warping, denting, and deformation under heavy commercial deck loads.
• Rugged Strongback Security: Employs a robust underside steel strongback assembly that anchors firmly against the perimeter rim to guarantee an unyielding, water-tight perimeter seal.
• Buna-N Chemical-Resistant Gasket: Fitted with a premium, industrial-grade Buna-N (Nitrile) rubber gasket that resists swelling or degradation from fuels, oils, and environmental weathering.
• Universal Shipyard Finish: Arrives shot-blasted and coated with a universal shipyard primer (painted), making the entire frame and cover assembly ready for immediate shipyard installation and custom top-coating.

• Qualified Personnel Requirement: Installation of the 20” single-bolt flush manhole must be performed by qualified marine welders or fitters in accordance with applicable classification society standards (ABS, DNV, Lloyd's).
• Surface Preparation & Alignment: The mounting frame must be aligned true and securely welded to clean, flat, and structurally sound deck plating to prevent distortion or twisting of the sealing seat.
• Mechanical Verification: After welding, verify that the central bolt rotates freely and that the strongback engages the underside lips smoothly without binding or catching.
• Debris Inspection: Prior to final closing, clear all sealing tracks and gasket faces of weld spatter, slag, rust, or excess paint to protect the gasket and ensure a drop-tight seal.
• Torque Specifications: Always follow recommended torque guidelines for the central bolt to avoid over-compressing the gasket or stripping the mechanical threads.