Restrained Ductile Iron Pipe Joint With Positive Lock Segments
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Solution Overview
Problem
Conventional ductile iron pipe joints lack resistance to thrust forces, particularly at bends, T-connections, reducers, and dead ends, requiring external thrust blocks or complex restrained joints that are difficult to assemble and limit the applications of ductile iron pipes.
Innovation Solution
A positive lock system for restrained joints in ductile iron spun pipes and fittings, featuring a bell-shaped socket, plain end with a weld bead, radially compressed elastomer gasket, and series of lock segments that transfer thrust loads to a locking chamber, allowing for self-restraining joints without external blocks, enabling quick assembly and high traction capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional push-on joints are used, then the joint is simple to assemble, but the joint offers no significant resistance to thrust forces
Solution Approach 1:
The locking mechanism is divided into multiple lock segments (typically 3-6 segments) that are distributed around the circumference of the spigot. Each segment independently engages with the socket wall, providing distributed thrust resistance while maintaining simple assembly through gravity-assisted insertion followed by rotational locking.
Solution Approach 2:
The lock segments are designed to rotate from an initial insertion position to a final locked position where they engage with the socket wall. This dynamic transition allows the joint to progress from easy assembly to high-strength thrust resistance automatically, combining the benefits of both simplicity and strength.
2Strength
If restrained joints with multiple components are used, then the resistance to thrust forces is improved, but the assembly complexity and time increase significantly
Solution Approach 1:
The locking mechanism integrates the thrust resistance function and the connection function into a single unified structure. The lock segments are directly attached to the spigot and engage with the socket, eliminating the need for separate thrust blocks, glands, tensioning rings, and multiple fastening components required by conventional restrained joints.
Solution Approach 2:
The lock segments serve multiple functions simultaneously: they provide thrust resistance, maintain joint alignment, enable angular deflection, and prevent separation. This multi-functionality replaces the need for multiple specialized components in conventional restrained joint systems.
3Strength
If conventional restrained joints are used, then the thrust force resistance is improved, but the assembly time and difficulty increase
Solution Approach 1:
The lock segments are pre-positioned on the spigot in an unlocked state that allows easy insertion into the socket. Once inserted, the segments automatically rotate into their locked position, providing thrust resistance without requiring additional assembly steps. This preliminary positioning eliminates the need for post-assembly tightening or adjustment operations.
4Strength
If thrust blocks are used to resist thrust forces, then the thrust resistance is improved, but the device complexity and installation difficulty increase
Solution Approach 1:
The thrust resistance function is extracted from external thrust blocks and integrated directly into the joint structure itself. The lock segments provide all necessary thrust resistance at the joint location, eliminating the need for separate external thrust blocks and their associated foundation requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The positive lock system effectively absorbs axial loads, allows for high-pressure ratings, reduces assembly time and components, and expands the application scope of ductile iron pipes to include trenchless laying, seismic zones, and challenging terrain without the need for thrust blocks.
Implementation Method 1
radially compressed elastomer gasket
Implementation Method 2
a weld bead, made on plain end of pipe at suitable location
Data Source
Figure 1~3
Figure 4~6
AI summary
This present invention relates to novel positive lock system for restrained joints of ductile iron spun pipes and fittings which are able to take all the thrust loads produced due to transmitting fluids pressure and provide certain angular deflections to the axis of two pipes. For ductile iron pipe to be joined, a socket (bell shape) and a spigot (plain end) sections are provided in pipes. For joining plain end is inserted in bell shape end. As the water pressure surges, the joint tends to disengage due to increasing axial loads. To take these axial loads, a circumferential chamber is provided in bell shape end and plain end is provided with a weld bead of suitable size. Axial forces generated due to water pressure is transmitted to pipe socket through welding via locking segments. Locking segments are inserted in circumferential chamber and they stays between chamber and welding bead. Circumferential chamber has suitable clearances to provide the required angular deviations at the joint.