Thermal Flowmeter Sealing and Assembly Mechanism
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Solution Overview
Problem
Existing thermal flowmeters face inefficiencies in mounting the measuring tube due to large casing sizes and poor sealing, with the ferrule prone to deformation causing leaks and requiring frequent nut retightening, and the measuring tube's rotation during assembly affecting sensor position stability.
Innovation Solution
A compact thermal flowmeter design with a cylindrical ferrule and joint shaft, where the joint shaft is movable and supported by the casing, and a screw mechanism outside the casing for assembly, preventing rotational force transmission and allowing for retightening without disassembly, using a spring to maintain sealing pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the nut is fastened inside the casing to attach the measuring tube to the joint shaft, then the measuring tube can be securely fixed, but the work efficiency for attaching the measuring tube is low and the casing size must be increased
Solution Approach 1:
The attachment mechanism is segmented into two parts: the joint shaft with external thread that protrudes from the casing, and the separate nut that is fastened outside the casing. This allows the fastening operation to be performed externally, improving work efficiency while maintaining secure fixation of the measuring tube through the joint shaft-nut connection
Solution Approach 2:
The joint shaft serves as an intermediary component that extends the connection interface outside the casing. By providing an external threaded portion, it enables the nut to be fastened externally while still achieving internal secure fixation of the measuring tube, thus resolving the contradiction between accessibility and secure attachment
2Reliability
If the first and second tapered surfaces are formed with a large area to ensure sealing effect, then the sealing between measuring tube and joint shaft is improved, but the outer diameter of the ferrule and joint shaft increases, leading to larger casing size
Solution Approach 1:
The sealing mechanism transitions from relying on large-area tapered surfaces to using a rubber O-ring seal. This parameter change in the sealing approach allows effective sealing with smaller contact areas, reducing the outer diameters of the ferrule and joint shaft, and consequently reducing the casing size while maintaining reliable sealing
3Reliability
If the ferrule is formed of resin material to enable contraction for sealing, then the sealing effect is improved, but the ferrule is prone to plastic deformation and cold flow, requiring periodic retightening
Solution Approach 1:
The rubber O-ring seal is designed as a replaceable component that can be easily removed and replaced. Instead of relying on the long-term dimensional stability of the resin ferrule, the sealing function is transferred to the O-ring which can be periodically replaced when worn, maintaining sealing reliability without requiring complex retightening mechanisms
Solution Approach 2:
The rubber O-ring acts as an intermediary sealing element between the measuring tube and the joint shaft/ferrule assembly. This intermediary component provides consistent sealing pressure and compensates for dimensional variations and wear, resolving the stability issue of the resin ferrule while maintaining effective sealing
4Ease of manufacture
If the measuring tube is inserted through the ferrule and joint shaft during assembly, then the assembly process is simplified, but rotational force is transmitted to the measuring tube causing sensor position instability
Solution Approach 1:
The joint shaft serves as an intermediary that decouples the rotational motion of the nut from the measuring tube. The measuring tube passes through the joint shaft without direct threaded engagement, so when the nut is fastened on the external thread of the joint shaft, rotation occurs in the joint shaft rather than the measuring tube, maintaining sensor position stability while keeping the assembly process simple
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 reduces casing size, improves mounting efficiency, maintains sealing effectiveness by compensating for pressure loss, and ensures consistent sensor positioning, enhancing manufacturing stability and ease of assembly.
Implementation Method 1
a spring that applies a pressing force to the joint shaft
Implementation Method 2
a sensor for detecting a flow rate having a heating element and provided in the measuring tube
Data Source
AI summary
A thermal flowmeter includes a casing, a ferrule, a measuring tube penetrating through the ferrule, a sensor for flow rate detection, a joint shaft movably supported by end portions of the casing, one end portion of the joint shaft being connected to the measuring tube and the ferrule with a through hole of the joint shaft and a hollow portion of the measuring tube communicating with each other, the other end portion of the joint shaft sticking out of the casing, and a screw thread-fitted to each of the end portions of the casing, and including a pressing portion pressing the joint shaft into an inside of the casing. A seal structure includes a first tapered surface formed on the ferrule and a second tapered surface formed on the joint shaft and fitting the first tapered surface, and is provided between the ferrule and the joint shaft.