Emergency Shutdown System

At gas stations, which power our daily lives, safety always comes first. You may have noticed that besides the fuel nozzle, display screen, and keyboard, there are some less conspicuous but crucial safety devices. Among them, the emergency shutdown system serves as the "last line of defense" and "lifeline" in the entire fueling station safety system. It can swiftly cut off the fuel supply in the event of an accident, effectively preventing serious incidents such as fuel leaks, fires, or even explosions. This system primarily consists of two core components: the pull valve and the emergency stop button.

1、 The First Line of Defense: The Pull-Off Valve – The "Safety Rope" Against Unexpected Pulling

Imagine a scenario where a car owner leaves the fuel nozzle in the tank after refueling and drives away. This seemingly minor mistake actually occurs in real life. Without protective measures, the immense pulling force could tear the fuel hose, causing a massive fuel spill. If exposed to static electricity or an open flame, the consequences would be catastrophic. In such cases, the pull-apart valve plays a crucial role.

(1) What is a pull-off valve?

The pull-off valve is a precision mechanical device installed at the connection between the fuel dispenser's flexible hose and the nozzle. Its primary function is to automatically and swiftly break into two parts when the hose is subjected to excessive tension beyond safe limits, while simultaneously sealing both ends of the fuel line to prevent fuel leakage.

(2) How does it work?

The working principle of the rupture disk can be summarized as "sacrificing the self to safeguard the greater good." It contains a precisely designed mechanical structure, typically made from special materials, with its fracture strength meticulously calculated.

l Normal Condition: During routine refueling, the breakaway valve serves as a robust connection that ensures fuel flows smoothly to the nozzle.

l Unexpected occurrence: When the movement of the vehicle causes an unintended pull on the hose and the force reaches a preset critical value (typically between 60-80 kilograms-force), the mechanical structure inside the breakaway valve is triggered.

l Automatic shut-off: The valve body breaks apart at the predetermined position, separating into two parts. Most critically, at the moment of separation, the built-in spring or valve core inside the valve body rapidly pops out within milliseconds, sealing the passages of both broken ends. It functions like two automatically closing faucets, instantly halting the flow of fuel.

l Post-incident handling: After an accident, the gas station staff only need to replace a new pull-off valve (a component that can be quickly replaced) and conduct safety inspections on the hose and other parts. The fuel dispenser can then resume normal operation. The cost of this process is minimal, yet it prevents a potentially catastrophic accident.

The pull-off valve is a standard feature of modern fuel nozzles and serves as a critical component in ensuring physical safety during on-site operations.

2、 Second line of defense: emergency stop button - a "red alert" that controls the entire situation

If the pull off valve is the best response for a single, local accident, then the emergency stop button is the global controller for dealing with larger emergency situations.

(1) What is an emergency stop button?

The emergency stop button is often labeled as an "emergency stop" interface (such as STOP interface) or an emergency stop board (JT100A). It is usually a prominent red button installed in a very visible and easily accessible location on the refueling island or station building, with the button labeled "emergency stop" or similar words. Its design follows the principle of "one hit, one stop" that humans intuitively respond to in emergency situations.

(2) How does it work?

The essence of the emergency stop button is a "master switch" connected in series throughout the power control system of the refueling engine. Its linkage mechanism involves multiple levels of electrical control:

l Trigger signal: When the staff or anyone discovers an emergency situation such as a fire, a large amount of fuel leakage, or a vehicle smoking or catching fire, press the emergency stop button firmly.

l Signal transmission: After the button is pressed, an emergency stop signal will be sent. According to the description of "Electrical Principles of Fuel Dispensers" in the textbook, this signal will be directly transmitted to the control board and power control board through the emergency stop interface (such as the STOP interface of the motherboard).

l Execution action: After receiving the emergency stop signal, the control board will immediately execute a series of chain reactions:

l Cut off motor power: For self-priming pump refueling machines, the power supply to the explosion-proof motor will be immediately cut off, the oil pump will stop running, and the oil supply will be stopped from the source.

l Turn off the submersible pump: For submersible pump refueling machines, the signal will cut off the power supply to the submersible pump through the control cabinet, causing the pump of the underground oil tank to stop working.

l Close the solenoid valve: At the same time, the control board will send a command to the drive board (such as QD500), and the drive board will immediately cut off the signal to the solenoid valve. According to the working principle of the solenoid valve, after the solenoid valve loses power, its internal valve core will quickly reset under the action of the spring, tightly closing the oil circuit. Even if the oil pump has stopped, it can prevent the residual oil in the pipeline from flowing out.

l System lockout: At the software level, the control motherboard will enter an emergency stop state, and the keyboard and display screen will usually display specific error codes, indicating that the system has been urgently stopped and no refueling operations can be performed until the emergency stop button is reset.

(3) The synergistic effect of the linkage mechanism

The disconnect valve and emergency stop button do not work in isolation, they together form a three-dimensional safety protection network. For example, when the disconnect valve is accidentally pulled and activated, although it has already cut off the leakage point, if the on-site situation is complex, the staff can press the emergency stop button without hesitation to ensure that the oil and electrical circuits of the entire gas machine and even the entire gas station are completely cut off, creating an absolutely safe environment for subsequent processing.

3、 Daily maintenance and importance of emergency shutdown system

The reliability of such an important system is crucial, and regular maintenance and inspection are essential

(1) Regular functional testing: Gas station staff should regularly (such as monthly) test the function of the emergency stop button to ensure that it stops working immediately and cuts off the power supply when pressed.

(2) Appearance inspection: Check for visible damage, cracks, or oil corrosion on the rupture valve. Check if the emergency stop button is intact and if the markings are clear.

(3) Professional maintenance: If any abnormalities are found, they should be reported for repair immediately. Replacing the disconnect valve or repairing the emergency stop circuit must be carried out by professional technicians in accordance with specifications to ensure its explosion-proof performance and functional integrity.

summary

The emergency cut-off system of the fuel dispenser has built an efficient and reliable safety barrier for us through the "local precise stop loss" of the pull off valve and the "global one key power-off" of the emergency stop button. Their design fully embodies the concept of "safety first, prevention oriented". Understanding the working principles of these 'behind the scenes heroes' not only increases our confidence in modern gas station safety technology, but also reminds us that while enjoying convenient services, everyone should abide by safety regulations and work together with technological progress to safeguard the safety around us.