Gas Valve Train for Modern Gas Burners

Understanding Gas Valve Trains in Burners.

The output temperature of the fuel-burning system in the industrial boiler and burner is controlled by the gas valve trains. Valve trains contain pipes, valves, switches, and regulators. It is designed to safely monitor, control, regulate, and manage the fuel gas entering the burners and boilers’ operation.

The function of the gas valve train is to control and manage the gas pressure by keeping it at the predetermined proper limits for efficient operation and optimum safety. It regulates the gas quantities required for optimizing and efficient operation.

It applies all safety precautions to detect and deal with hazards like gas leaks, over and under pressure, and unsafe operation to avoid human risks and equipment damage by shutting down the main gas supply.

The gas valve train is connected to the main automation system and controlled via a PLC program to ensure the safety and efficient operation of the gas valve train and the gas burner.

What are the components of Gas Valve Trains?

Gas Train Valve

Normally the gas valve trains contain many devices and instrumentations required to achieve the objectives of this train valve. These devices include the following according to the above image:

• Gas supply (1).

• Strainer or gas filter (2).

• Needle or ball valve (3).

• Pressure indicator PI (4).

• High-pressure switch HPS (5).

• Temperature indicator TI (6).

• Main manual valve (7).

• Gas pressure regulator (8).

• Automatic upstream shut-off (9).

• Manual valves (10).

• Manual valves (11).

• Gas flow meter (12).

• Automatic vent shut-off valve (13).

• Manual valve (14).

• Automatic downstream shut-off valves (15).

• Gas flow control valve (16).

• Low-pressure switch LPS (17).

• Gas burner (18)

A short brief of each item in the gas train valve is explained in the next part to show the type of this device, its function, and the importance of its rule in

Gas supply (1).

The gas supply is the source of the gas fed to the gas valve train from the national gas utility grid through a gas reduction station where the gas pressure is reduced from a high pressure to a low pressure suitable for the burner operated by the gas valve train.

Strainer or gas filter (2).

The gas filter or strain protects the gas train unit devices from strange particle damage or malfunction of sensitive devices like meters, gas regulators, valves, and burners. It removes particles, dirt, and debris from entering the gas train. Typically, it consists of a metal screen or fine mesh.

Needle or ball valve (3).

This valve is used as a manual valve to isolate the pressure gauge (4) device in case of maintenance or replacement.

Pressure indicator PI (4).

The pressure indicator is installed to display the gas pressure value. This device could be a pressure gauge or a digital pressure transmitter that displays the pressure value digitally. Sometimes both devices confirm the reading to ensure efficient and safe operation.

High-pressure switch HPS and Low-pressure switch LPS (5) and (17).

These switches control the unit pressure at the upstream and downstream respectively according to a preset pressure value. If the main pressure from the supply goes below this preset value or the downstream pressure exceeds the preset value. They trigger an alarm and shut down the system for human and equipment safety.

Temperature indicator TI (6).

This device is a monitor same as the pressure indicator but for the gas temperature. Gas temperature affects the gas flow and heat consumption. It reflects the efficiency of the combustion and performance of the gas burning.

Main manual valve (7).

The valve closes and opens manually to isolate the valve train and prevent the gas flow to the next devices manually during the system’s maintenance or replacement of any device in the gas unit.

Gas pressure regulator (8).

It is one of the key components in the gas valve train. It controls the gas pressure by reducing the high pressure from the source to a lower value and regulating it to a desired pressure value for the downstream devices to control the system’s output temperature. It keeps the operation condition safe. Normally this controller works mechanically.

Automatic upstream shut-off (9) and downstream (15) valves.

The rule of these valves is to open and close electrically according to an electrical signal from the main computer that controls the operation of the gas train valves and the main process based on a preset operation program. One is installed at the upstream part and the other at the downstream.

Manual valves (10), (11), and (14).

These 3 manual valves typically have the same operation and function as the valve (7), they are used only during the maintenance or replacement of the flow meter (12) without stopping the operation. In normal operation, the valves (10) and (14) are opened while the valve (11) is closed. During replacement of the flow meter (12), the valves (10) and (14) are closed and valve (11) is open. Valve (11) is called the bypass valve.

Gas flow meter (12).

The gas flow meter monitors the gas flow through the burner. It has the same importance as the gas flow control valve (16). They are working together to keep the output temperature at the desired value all the time.

The gas train’s PID controller can work with the flow control to control the gas flow rate or, it could be worked to keep the output temperature. In that case, there will be a cascaded 2 controller where the main is the temperature control and its output will be the flow setpoint of the second controller.

Automatic vent shut-off valves (13).

This shut-off valve has the same concept as the shut-off (9). It is critical safety equipment in the train valve, which passes the excess gas in the pipe during abnormal operation or shutdown to the open air through the pipe (19). The vent valve opens or closes according to the main program.

Gas flow control valve (16).

As mentioned, the gas flow control valve controls the gas flow rate delivered to the burner. It keeps the gas flow rate at its required flow set point. It plays a critical role in the fuel-to-air ratio to optimize the efficiency and safety operation of the gas train valve.

Gas burner (18).

 The gas burner is designed especially for natural gas fuel to get maximum combustion efficiency from burning gas and air. Normally the burner is equipped with an ignitor to have the first spark to light on the burner flame.

The devices used in the gas train valve (control, protection, and measurements are vary depending on the application and safety of the burning process. However, the devices explained in this article are the main and critical devices used commonly. A detail of each device could be discussed later in separate articles.