Hydrostatic Mechanical Face Seal for Stable Controlled Leakage
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Solution Overview
Problem
In pressurized water nuclear power plants, existing pump shaft seal assemblies face challenges in maintaining minimal leakage while withstanding high pressures and temperatures, with manufacturing tolerances, contact friction, and thermoelastic deformation influencing leakage rates, necessitating a design that optimizes for stable and controlled leakage.
Innovation Solution
A controlled leakage mechanical face seal design featuring a rotating and stationary seal support ring with face plates having sealing surfaces, where hydrostatic forces maintain the face plates against the support rings without mechanical force, and the sealing surfaces have contoured, tapered, or stepped configurations to manage pressure distribution and leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional mechanical seal assemblies are used with mechanical force to hold face plates, then sealing capability is improved, but manufacturing precision and assembly complexity increase
Solution Approach 1:
The patent replaces the traditional mechanical force-based sealing system with a hydrostatic sealing system. Instead of using mechanical springs or actuators to press the face plates against the sealing surfaces, the invention uses hydrostatic pressure generated by the reactor coolant itself to maintain the sealing contact. This substitution eliminates the need for precise mechanical tolerances and complex assembly requirements while maintaining reliable sealing capability.
Solution Approach 2:
The invention employs hydrostatic pressure (a form of hydraulics) to achieve sealing. The reactor coolant under high pressure creates a hydrostatic force that automatically maintains the face plates in contact with the sealing surfaces. This hydraulic approach leverages the existing system pressure to provide sealing force, eliminating the need for separate mechanical forcing mechanisms and reducing manufacturing precision requirements.
2Manufacturing precision
If hydrostatic forces are used to hold face plates without mechanical force, then manufacturing precision requirements are reduced, but seal design complexity increases
Solution Approach 1:
The hydrostatic sealing system is self-regulating and requires no external control mechanisms. The reactor coolant pressure automatically generates the necessary hydrostatic force to maintain sealing contact. The system serves itself by using the process fluid (reactor coolant) to provide the sealing force, eliminating the need for additional actuators, sensors, or control systems that would increase design complexity.
Solution Approach 2:
The invention changes the fundamental parameter of sealing force generation from mechanical (active forcing) to hydrostatic (passive pressure-based). By utilizing the existing high pressure of the reactor coolant system, the design transforms the sealing mechanism to rely on pressure distribution rather than mechanical force application. This parameter change simplifies the overall design by eliminating mechanical forcing components while accepting the inherent complexity of hydrostatic pressure distribution.
3Reliability
If contoured, tapered, or stepped sealing surfaces are used, then leakage control is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies different geometric configurations (contoured, tapered, or stepped) to specific local regions of the sealing surfaces rather than requiring complex geometries throughout the entire seal assembly. Each local region is optimized for its specific function: certain areas may be contoured to distribute pressure, others tapered to control leakage paths, and others stepped to manage fluid flow. This localized application of different geometries improves leakage control while keeping overall manufacturing complexity manageable.
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 design achieves a stable and minimal leakage rate, reducing the impact of manufacturing tolerances and thermoelastic deformation, ensuring consistent coolant flow and maintaining equilibrium in the reactor coolant system.
Implementation Method 1
the seal support rings and the face plates are configured so that during operation of the pump the hydrostatic forces on the first sealing surface and the second sealing surface are sufficient to hold the first face plate against the first seal support ring and the second face plate against the second seal support ring
Implementation Method 2
maintaining constant separation by a thin fluid film between the seal faces
Data Source
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AI summary
A controlled leakage, hydrostatic, mechanical seal that eliminates sources of contact friction; advantageously locating contact friction forces to be in alignment with the seal face centroid; optimizes the seal face design to achieve maximum hydrostatic film stiffness and minimum sensitivity to radial taper; eliminating unnecessary O-rings and other sources of significant force variation; utilizes a design-for-manufacture approach to design hardware that can be consistently manufactured to precise tolerances; optimizes the double delta channel seal to achieve adequate compression, minimal frictional drag force, and maximum wear resistance; eliminates sources of circumferential waviness such as bolt preload and other non-axisymmetric features; and, thermally isolates components of different materials to mitigate the deformation due to differential thermal expansion.