Butterfly Valve Bushing Gap to Prevent Stem-Hole Resin Breakage
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Solution Overview
Problem
Butterfly valves with metal core members coated in synthetic resin face issues with fluid pressure causing deformation and leakage, especially when the resin material around the valve-stem hole is subjected to reaction forces from the valve stem, leading to potential breakage and leakage of corrosive fluids.
Innovation Solution
A butterfly valve design featuring a valve element with a core member and a contour member made of resin, where the valve stem is supported by a bushing with a gap between the inner peripheral surface of the bushing and the outer peripheral surface of the valve stem, preventing the transmission of reaction forces to the resin material and reducing the risk of breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the valve stem is directly supported in the bearing holes and valve-stem hole without a bushing, then the device complexity is reduced, but the reliability deteriorates due to seizure risk and leakage
Solution Approach 1:
A bushing made of synthetic resin material is introduced as an intermediary component between the valve stem and the bearing holes/valve-stem hole. The bushing rotatably supports the valve stem while providing sealing function, preventing direct contact between metal parts to avoid seizure and preventing fluid leakage, thus resolving the contradiction between structural simplicity and sealing reliability
2Object-affected harmful factors
If the core member is completely covered with synthetic resin material to prevent corrosion, then the corrosion resistance is improved, but the strength deteriorates when large fluid pressure acts on the valve element
Solution Approach 1:
The valve element is constructed as a composite structure with a metal core member providing mechanical strength and a synthetic resin coating providing corrosion resistance. This composite material approach allows the valve element to withstand large fluid pressures while resisting corrosion from corrosive liquids
Solution Approach 2:
The valve element is divided into functional segments: the core member handles mechanical loading and structural integrity, while the resin coating handles chemical resistance. This segmentation of functions allows each material to optimize its specific role
3Ease of manufacture
If the bearing holes have an inner diameter slightly larger than the valve stem outer diameter to absorb machining errors, then the ease of manufacture is improved, but the reliability worsens due to valve stem movement causing deformation and leakage
Solution Approach 1:
The bushing acts as an intermediary that absorbs the gap between the valve stem and bearing holes. It provides a precise fit for the valve stem while being accommodated within the bearing holes with machining tolerances, preventing valve stem movement that would cause deformation and leakage while maintaining ease of manufacture
4Reliability
If a bushing is provided to rotatably support the valve stem and provide sealing, then the sealing reliability is improved, but the device complexity increases
Solution Approach 1:
The bushing is designed to perform multiple functions simultaneously: it provides rotational support for the valve stem, prevents seizure between metal parts, and provides sealing to prevent fluid leakage. This multi-functionality reduces the need for separate components, thereby limiting the increase in device complexity while achieving improved reliability
Data Source
AI summary
A butterfly valve includes a valve body, a valve stem rotatably supported by the valve body, a valve element rotatably supported by the valve body, and a bushing externally fitted around the valve stem. The valve element is configured by a core member and a contour member formed of a resin material and surrounding the core member to define a contour of the valve element, the valve element is formed with valve-stem holes that support the valve stem via the bushing, the contour member has a stem hole component forming inner peripheral surfaces of the valve-stem holes, and the bushing and the valve stem have shapes such that a gap is formed between an inner peripheral surface of a portion of the bushing located inside the stem hole component and an outer peripheral surface of a portion of the valve stem located inside the stem hole component.