During the refueling process of billions of vehicles every day, the light fuel gun and hose connected to it in the hands of the refueling staff form the most familiar scene of a gas station. However, behind this seemingly simple operation lies precise mechanical design, classic physical principles, and advanced materials science. They are not only channels for fuel delivery, but also key guarantees for safety, environmental protection, and precise metering. This article will take you on a deep exploration of the technological world of self sealing oil guns and refueling hoses.
1. Self sealing oil gun - an intelligent safety guard for refueling operations
Self sealing oil gun is the core terminal component of modern fuel dispensers, whose core mission is to improve efficiency while preventing oil spillage and ensuring operational safety.
(1) Core Structure: Precise Mechanical Assembly
According to technical data, a typical self sealing oil gun is mainly composed of the following components:
Gun body structure: including main valve, auxiliary valve (used to control flow rate), trigger lever mechanism.
Self sealing sensing system: This is the "brain" of the oil gun, including the sensing chamber (diaphragm chamber), vacuum channel (Venturi effect application), reset spring, etc. In some models, a float valve is also included as an auxiliary or main sensing mechanism.
Oil outlet and oil and gas recovery system: The oil outlet is responsible for guiding the oil into the tank; The oil and gas recovery hole next to it is responsible for synchronously extracting oil vapor during refueling, achieving environmentally friendly recovery.
Connection mechanism: A quick connector connected to the rubber hose to ensure reliable connection of the oil, gas, and electrical circuits (conducting static electricity).
(2) Working principle: Physics behind the 'jump gun'
The scientific name of the "jump gun" is "automatic closing function", and its implementation mainly relies on two classic physical principles: the Venturi effect and the float valve mechanism.
l Venturi effect and negative pressure triggering mechanism (mainstream principle)
This is the core principle currently used by the vast majority of self sealing oil guns.
Venturi tube design: In the oil circuit inside the oil gun, there is a specially designed narrow passage, which is a miniature Venturi tube. When fuel flows through this area at high speed under pump pressure, according to the Bernoulli principle in fluid mechanics, the faster the flow rate, the lower the pressure generated by the fluid. Therefore, a local low-pressure zone (negative pressure zone) will be generated in this narrow area.
Sensing channel: This low-pressure area is connected to the sensing chamber at the front end of the oil gun through an extremely thin channel. The other side of the sensing chamber is connected to the atmosphere through an air inlet. Under normal refueling conditions, the nozzle of the fuel gun is exposed to the air, and the pressure inside and outside the sensing chamber is balanced.
At the moment when the "jump gun" is triggered: when the oil level in the tank gradually rises and eventually submerges the oil nozzle of the oil gun, the channel connecting the sensing chamber and the outside is blocked by the oil. At this point, the sensing chamber forms a closed space. However, the low pressure at the Venturi tube continues to 'suck' this enclosed space, causing a rapid decrease in pressure inside the chamber and creating a significant negative pressure.
Mechanical action: The diaphragm inside the sensing chamber is pushed upwards by the pressure difference between atmospheric pressure and negative pressure inside the chamber. This small displacement is released by a precise lever mechanism, which releases the main valve switch that is stuck by the trigger. Under the action of the strong reset spring, the main valve instantly closes, cutting off the oil circuit, and the oil gun makes a "click" sound, completing the "jump gun".
Simple metaphor: Just like when you drink a beverage with a straw, when you block the top of the straw with your fingers and lift it up, the beverage will not drip because negative pressure is formed inside the straw. When the sensing chamber of the oil gun is blocked, similar to this, the internal negative pressure triggers the closing device.
l Float valve auxiliary/triggering mechanism
Some oil gun models (such as certain OPW and ZVA oil guns) may integrate or use a float valve mechanism separately.
Structure: A lightweight float is installed inside the front end of the oil gun nozzle.
Working principle: When the oil level rises to contact the float, the float rises under buoyancy. The floating float directly lifts a top rod or pushes a small valve, which can also trigger the linkage mechanism to close the main valve.
The float valve mechanism is very intuitive and reliable, which can effectively deal with the rich oil foam, because foam can also provide enough buoyancy to trigger the closure. Many times, oil guns adopt a dual safety design of Venturi effect and float valve to ensure timely self sealing under any complex working conditions.
(3) Why do they frequently jump guns?
Once you understand the principle, it is easy to understand why the gun sometimes jumps frequently when refueling, which is usually not a malfunction:
Fuel tank structure: Some car models have tortuous fuel tank pipelines or anti wave plates, which makes it difficult for the oil flow to spread smoothly and can easily form temporary blockages at the nozzle of the fuel gun, triggering gun jumping.
The refueling speed is too fast: when refueling with large flow, the oil will roll violently in the oil tank, producing foam, and the foam may block the sensing port in advance.
Impact of oil and gas recovery system: If the oil and gas recovery system of the vehicle or fuel dispenser is not smooth, the pressure in the fuel tank will increase, which will hinder the smooth flow of oil and intensify oil splashing, which can easily trigger self sealing.
2. Refueling hose - a masterpiece of materials science in balancing
The hose connecting the oil gun and the refueling machine is not a simple "rubber hose". It needs to meet multiple conflicting requirements such as oil resistance, compression resistance, flexibility, wear resistance, and electrostatic conductivity under extreme working conditions, and is a model of the "balance" in materials science.
(1) Multi layer composite structure: collaborative design with each performing its own duties
The refueling hose is a typical composite hose, usually composed of three layers, each layer has its irreplaceable function:
l Inner lining layer: the "first line of defense" against oil and corrosion
Material: Mainly made of nitrile rubber (NBR). Nitrile rubber has excellent resistance to non-polar mineral oils, gasoline, diesel, etc. due to the presence of highly polar cyanide groups (CN) in its molecular structure, and is not easily swollen, softened, or degraded.
Process requirements: The inner wall must be smooth and flat to reduce fluid resistance, prevent oil residue and scaling, and ensure measurement accuracy.
l Enhancement layer: the "skeletal system" that bears pressure
Material and structure: This is the source of the "power" of the rubber hose. Traditionally, high-strength synthetic fibers (such as polyester and aramid) or steel wires are used for weaving or winding. Modern high-performance rubber hoses often use fiber and steel wire mixed weaving or full aramid weaving.
Fiber layer: The advantage is lightweight and good flexibility.
Steel wire layer: The advantage is extremely high strength and excellent compressive performance, but it is heavy and has a large bending radius.
Aramid fiber: known as "synthetic steel wire", it has excellent properties such as high strength, high modulus, lightweight, and fatigue resistance, making it an ideal material for manufacturing high-performance fuel hoses.
Function: The reinforcement layer acts like a sturdy cage, restraining the inner lining layer and withstanding the internal pressure generated by the fuel pump (usually 0.30.5MPa), preventing the hose from expanding, deforming, or even bursting under pressure.
l Outer coating: Wear resistant and weather resistant "protective outerwear"
Material: Typically, chloroprene rubber (CR) or chlorosulfonated polyethylene (CSM) is used. These materials have excellent ozone resistance, UV resistance, wear resistance, acid and alkali resistance, and flame retardant properties.
Function: Protect the internal reinforcement layer and lining layer, resist sun and rain, friction with the ground, occasional vehicle crushing, and erosion from various chemicals. The durability of the outer coating directly determines the service life of the hose.
Key design: Conductive wires must be embedded in the outer coating. This wire (usually a spiral wound copper or stainless steel wire) is connected to the metal joints at both ends to ensure a continuous conductive path between the oil gun, hose, and refueling machine body. It promptly guides the static electricity generated by oil flow friction into the ground, completely eliminating the risk of static sparks igniting oil vapor.
(3) The Art of Balancing Performance
Creating a good fuel hose is a constant process of balancing and compromising:
Balance between oil resistance and flexibility: The purer the nitrile rubber, the better its oil resistance, but it usually becomes harder and brittle. By adding special plasticizers and elastomers, the low-temperature flexibility of the hose can be significantly improved while minimizing the sacrifice of oil resistance, allowing it to operate flexibly even in harsh winter.
Balance between strength and weight: Although all steel wire reinforcement has the highest strength, its excessive weight makes it difficult to operate and prone to fatigue damage due to repeated dragging. By using high-tech fibers such as aramid, the weight of the hose can be significantly reduced while maintaining the same or even higher working pressure, improving user experience and durability.
Balance between durability and cost: High performance materials such as aramid and special synthetic rubber will inevitably lead to an increase in cost. Manufacturers need to choose the most suitable material ratio and structural design based on the frequency of use, harsh environmental conditions (such as coastal high salt spray areas), and target market of the fuel dispenser to achieve the best economy.
3. Collaborative work and daily maintenance
The oil gun and rubber hose are an inseparable system. The sensitivity and self sealing of the oil gun depend on the stable oil pressure conveyed by the hose; The static electricity safety of the hose ultimately needs to be achieved through the contact between the metal parts of the oil gun and the fuel tank port. Any malfunction of either party may affect the safety and performance of the entire system.
Daily maintenance points:
Oil gun: Keep the nozzle of the oil gun clean to prevent impurities from blocking the sensing hole; Avoid forcefully bumping; If there is oil leakage or failure to self seal, it should be immediately stopped and reported for repair.
Rubber hose: Regularly check the outer coating for cracks, bulges, hardening, or signs of severe wear; Ensure that the rubber hose is placed in its natural state to avoid excessive twisting or bending; Vehicles are strictly prohibited from crushing.
summary
These two key components of the fuel dispenser fully embody the connotation of "small parts, big technology". They are not only tools for achieving fuel filling functions, but also precision products that integrate mechanical engineering, fluid mechanics, materials science, and safety design. Every safe and smooth refueling experience relies on their reliable work behind the scenes. With the development of technology, lighter, smarter (such as integrated flow sensors), and more environmentally friendly (such as bio based materials) oil guns and hoses will continue to drive refueling equipment towards safer, more efficient, and greener directions.
