Fuel Priming Circuit with Isolation Chamber
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Solution Overview
Problem
Users often mistake the purge pump for the prime pump in small internal combustion engines, leading to incomplete carburetor purging or flooding, making engine starting difficult due to incorrect operation of the manually actuated pumps.
Innovation Solution
A priming and purging fuel system that combines a start pump to supply liquid fuel to a priming circuit and fuel vapor and air to a purging circuit, using an enlarged isolation chamber and calibrated check valves to prevent flooding, ensuring proper carburetor priming and purging without fuel dribble during engine operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single manually actuated pump is used for both purging and priming, then the device complexity is reduced, but the ease of operation deteriorates due to user confusion between purge and prime functions
Solution Approach 1:
The single pump system is segmented into two distinct functional circuits: a purging circuit with a first check valve and a priming circuit with a second check valve. This segmentation allows the pump to serve both functions while maintaining operational clarity through separate flow paths and controlled fuel delivery mechanisms.
Solution Approach 2:
Check valves are introduced as intermediary components that mediate between the manually actuated pump and the carburetor. The first check valve controls purging flow while the second check valve controls priming flow, preventing user error by ensuring fuel is delivered only through the appropriate circuit based on pump actuation state.
2Reliability
If the pump is actuated multiple times to ensure complete purging, then the purging effectiveness is improved, but the risk of flooding the engine increases
Solution Approach 1:
The system incorporates feedback through check valves that respond to pressure differentials and flow conditions. The first check valve allows purging flow when the pump is actuated, while the second check valve prevents priming fuel delivery until purging is complete, providing automatic feedback control that prevents flooding even with multiple pump actuations.
Solution Approach 2:
The purging circuit is designed to execute purging action first through the first check valve before the priming circuit can deliver fuel through the second check valve. This preliminary action ensures the carburetor is cleared of excess fuel vapor and liquid before priming fuel is introduced, preventing flooding regardless of the number of pump actuations.
3Object-affected harmful factors
If fuel flow is restricted to prevent flooding, then the risk of engine flooding is reduced, but the priming effectiveness deteriorates
Solution Approach 1:
The fuel flow restriction is made dynamic through the second check valve, which adjusts its opening based on pressure differential. During pump actuation, the check valve opens sufficiently to allow effective priming flow. During normal engine operation, the reduced pressure differential causes the check valve to close, preventing fuel dribble and flooding while maintaining priming effectiveness when needed.
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 system effectively purges stale fuel and vapor while priming the engine, ensuring reliable starting by preventing flooding and ensuring the correct flow of fuel without dribble into the engine, thus simplifying the starting procedure.
Implementation Method 1
A biased closed check valve in the conduit of the purging circuit is calibrated to remain closed until a sufficient differential pressure across the check valve is achieved whereupon the check valve cracks open and flows a portion of liquid fuel and vapor back to a fuel tank
Implementation Method 2
When actuated, the start pump increases fuel pressure in the conduit of the priming circuit and a diverging conduit of the purging circuit
Data Source
AI summary
A priming and purging fuel system for an internal combustion engine purges a diaphragm carburetor of the engine of stale liquid fuel and accumulated fuel vapor and air while simultaneously priming the carburetor and/or engine with liquid fuel for starting. A start pump of the fuel system supplies at least liquid fuel to a priming circuit and preferably at least fuel vapor and air to a purging circuit of the fuel system. The priming circuit delivers the priming fuel to the engine via a conduit that leads to an isolation chamber located between an inlet jet and preferably an outlet jet. The cross sectional flow area of the jets are appropriately sized to flow a needed amount of priming fuel to the carburetor and/or engine for starting without flooding the engine. The combination of the enlarged isolation chamber and jets, at least substantially prevents fuel dribble from the priming circuit and into the engine while running.