Split Circumferential Seal Lift-Off via Hydrodynamic Pressure
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Solution Overview
Problem
Conventional circumferential contact seals wear out quickly due to sliding contact with rotating shafts, while non-contacting gas film seals fail when liquid is present, leading to leakage issues in steam turbines and similar environments.
Innovation Solution
A circumferential shaft seal segment design featuring feed slots and recesses with varying ramp slopes, allowing for lift-off and reduced friction, effective in both gaseous and liquid environments by utilizing steam pressure for hydrodynamic balancing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If circumferential contact seals are used to control leakage, then sealing effectiveness is improved, but the seal rings wear out quickly due to sliding contact
Solution Approach 1:
The patent replaces the mechanical sliding contact system with a hydrodynamic fluid film system. Instead of relying on direct contact between seal rings and shaft, the invention uses a fluid film (gas or liquid) to carry the seal ring, eliminating wear while maintaining sealing effectiveness through pressure-driven lift-off.
Solution Approach 2:
The patent employs hydrodynamic sealing principles where pressurized fluid (gas or liquid) is routed through clearance spaces and cutouts to generate lift forces. The fluid pressure creates a separating force that lifts the seal ring off the shaft, eliminating contact wear while maintaining the seal integrity.
2Duration of action of moving object
If solid seals are spaced from the rotating shaft to avoid wear, then service life is improved, but leakage increases due to the gap
Solution Approach 1:
The patent uses hydrodynamic pressure generation where the fluid flowing through the gap creates positive pressure in recesses and cutouts. This pressure generates lift forces that maintain an optimized gap distance - large enough to prevent wear but small enough to maintain sealing effectiveness through pressure-driven fluid dynamics.
Solution Approach 2:
The patent changes the operational parameters of the gap by introducing pressurized fluid flow. The gap transitions from a passive leakage path to an active hydrodynamic bearing zone where fluid pressure parameters (flow rate, pressure, velocity) are controlled to generate lift forces that maintain optimal separation distance.
3Duration of action of moving object
If circumferential gas film seals are used to reduce friction and heat, then durability is improved, but performance fails when liquid or condensate is present
Solution Approach 1:
The patent designs a universal seal system that functions effectively with either gas or liquid as the lifting fluid. The hydrodynamic sealing mechanism works with both gaseous steam and liquid condensate, allowing the same seal structure to adapt to varying operating conditions including startup, shutdown, and different load conditions where the fluid state may change.
Solution Approach 2:
The patent creates a dynamic sealing system that automatically adapts to changing operating conditions. The hydrodynamic lift mechanism responds to the actual fluid present (gas or liquid) by adjusting the pressure distribution and lift forces accordingly, maintaining effective sealing whether the steam is in gaseous or condensed liquid form.
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 provides efficient sealing with reduced friction and leakage, maintaining performance across varying operating conditions, including startup when steam is in liquid form, by using steam pressure to lift the seal segments off the shaft.
Implementation Method 1
The recesses are configured with varying ramp slopes, allowing for lift-off and reduced friction, effective in both gaseous and liquid environments by utilizing steam pressure for hydrodynamic balancing
Implementation Method 2
utilizing steam pressure for hydrodynamic balancing
Implementation Method 3
Another alternative to circumferential contact seals is a circumferential gas film seal. Much like the circumferential contact seal, this seal includes one or more carbon seal rings that exert a very light contact force against the shaft when it is not rotating. The seal ring lifts-off the shaft or sleeve when the shaft is rotating.
Implementation Method 4
As the shaft rotates, gas entrained by the rotating shaft is compressed in these cutouts, and as the gas escapes over the non-recessed 'pads' between the recesses, it produces an additional pressure and flow of gas for maintaining a separation between the seal ring and the shaft.
Data Source
AI summary
A circumferential shaft seal segment has radial inner and outer faces and first and second axial faces, and at least one feed slot in the radial inner face extending from the first axial face toward the second axial face. At least one recess extends from the at least one feed slot and has first and second axially spaced side walls, a bottom between the side walls, a first end at the feed slot and a second end circumferentially spaced from the feed slot. The recess includes a first portion extending from the first end and a second portion extending from the second end, and a radial depth of the first portion is a first function of a distance from the feed slot and a radial depth of the second portion is a second, different, function of the distance from the feed slot.