Valve Shaft Passage Sealing for Low-Torque Pressure Isolation
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Solution Overview
Problem
Existing shaft passages for ball valves face challenges in maintaining secure seal tightness under pressure, particularly with refrigerant, and require high torque for movement due to thermal expansion and system pressure effects on the sealing membrane.
Innovation Solution
A shaft passage design featuring an inner and outer shaft seal, with the fluid shaft seal depressurized relative to the operating pressure, where the inner shaft seal absorbs the operating pressure, and the outer shaft seal acts as a replacement, ensuring good seal tightness and low torque requirements. This design includes axial and radial bearings for lubrication and annular gaps for thermal compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sealing membrane is acted upon by system pressure and thermal expansion occurs, then the outer shaft seal cannot seal sufficiently securely, but maintaining seal tightness under pressure is required
Solution Approach 1:
The shaft seal is divided into three separate sealing elements: an inner shaft seal, a fluid shaft seal, and an outer shaft seal. Each seal handles specific pressure conditions independently, with the inner seal absorbing the full operating pressure while the fluid shaft seal operates at depressurized conditions, preventing thermal expansion issues from affecting seal integrity
Solution Approach 2:
The fluid shaft seal acts as an intermediary between the inner and outer shaft seals. It is supplied with lubricating fluid through transverse bores and operates at a pressure lower than the system pressure, serving as a buffer that protects the outer shaft seal from the full impact of system pressure and thermal expansion forces
2Reliability
If the outer shaft seal is designed to seal the shaft passage under pressure, then seal tightness is improved, but torque required to move the shaft increases due to compression load
Solution Approach 1:
The sealing function is segmented across three separate shaft seals arranged in series. The inner shaft seal absorbs the full operating pressure of the refrigerant, while the fluid shaft seal and outer shaft seal operate at progressively lower pressures. This segmentation ensures that only the inner seal experiences high compression loads, minimizing the torque required to rotate the shaft while maintaining comprehensive seal tightness
Solution Approach 2:
Different regions of the shaft assembly have different pressure conditions tailored to their specific functions. The inner shaft seal region experiences full system pressure for primary sealing, while the fluid shaft seal region is depressurized through fluid supply bores to reduce friction and torque requirements, and the outer shaft seal region experiences minimal pressure for backup sealing
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 solution achieves secure seal tightness and reduced torque requirements by isolating the fluid shaft seal from the operating pressure, allowing the inner shaft seal to absorb pressure and the outer shaft seal to compensate for thermal expansion, thereby maintaining effective sealing and lubrication.
Implementation Method 1
the fluid shaft seal is depressurised compared with an operating pressure of the medium to be controlled. Only the inner or lower shaft seal, which is assigned, for example, to a regulating chamber or a pressure chamber of a medium to be controlled, is acted upon by the pressure of the medium flowing through or to be controlled
Implementation Method 2
the oil reservoir in the sealing membrane expands during thermal exposure
Data Source
AI summary
The invention relates to a shaft passage and a valve having such a shaft passage, as well as a method for producing a shaft passage, in which the shaft (21) has at least one drive portion (24) to which a drive for controlling the shaft (21) can be connected and has a connecting portion (25) opposite the drive portion (24), to which an actuating member (64) can be connected, and an inner shaft portion (26) in the through-bore (22) extending at least partially in the through bore (22), and having an inner shaft seal (36) to which an operating pressure of a medium to be controlled by the actuating member (64) is applied, and having a fluid shaft seal (34) which extends in the direction of the drive portion (24), and which is arranged between the inner shaft seal (34) and the outer shaft seal (42), wherein the fluid shaft seal (34) is formed between the through bore (22) and the inner shaft portion (26) of the shaft (21) and is pressure-relieved against an operating pressure of the medium to be controlled.