Introduction to Pressure Regulation in Common Rail Diesel (CRD) Systems
Teaching Common Rail Diesel (CRD) systems can be challenging without clear, accessible starting materials. That is why introductory resources on key components, such as the pressure regulator, are so valuable in the classroom.
This article presents a basic introduction to rail pressure regulation in CRD systems and a few introductory questions for formative assessment. It is designed as a practical starting point for teachers who want to explain how pressure in the common rail is controlled, how the regulator is constructed, and how it works within the CRD system.
Table of Contents
Introduction to Common Rail Diesel
CRD (Common Rail Diesel) is an electronically controlled fuel injection system fitted to modern diesel-powered trucks. It consists of a low-pressure and a high-pressure circuit.
It also contains:
- Various sensors that provide the electronic control unit (ECU) with information
- Actuators controlled by the ECU
Introduction to pressure regulation in CRD systems
2. High-pressure line to common rail. 3. Pressure regulator. 4. Low-pressure line (return circuit).
The pressure regulator is an actuator.
Using this actuator, the engine control unit controls the pressure in the common rail.
The pressure regulator is located in the high-pressure circuit of the fuel system. It is usually mounted on the high-pressure pump, but on some models, it is mounted on the common rail.
With the pressure regulator, the control unit creates a variable opening between the high-pressure circuit and the low-pressure circuit.
- If the rail pressure becomes too high, the control unit enlarges the opening.
- If the rail pressure is too low, the opening is reduced.
Try the Demo Module
Take a look at our CRD: High-Pressure Regulator demo module for heavy vehicles and enhance your lesson with a free, ready-to-use resource for explaining rail pressure regulation.
Pressure regulator construction
The pressure regulator is a solenoid valve and is made up of:
- A coil
- An anchor
- A spring
- A core
- A ball valve
You can see the regulator coil in the electrical diagram.
The working principle of the pressure regulator
The coil becomes magnetic when a current runs through it (electromagnet). The greater the current, the stronger the electromagnet. The electromagnet assists the spring in pushing the ball valve onto the seat. The ball valve closes due to the force of the spring.
Above 100 bar the rail pressure depends on the strength of the electromagnet. In other words, the rail pressure now depends on the current passing through the coil.
So, the engine control unit regulates the rail pressure by controlling the current passing through the pressure regulator.
- When the pressure is greater than 100 bar, the pressure is greater than the force of the spring and the valve opens.
- When there is no current flowing through the coil, the pressure is set to 100 bar.
- When a current is flowing through the coil, the force with which the armature closes the ball valve increases.
By adjusting the current, it is possible to achieve any pressure up to 1800 bar.
2. From 100 bar, the pressure regulator opens, the pressure does not rise further than 100 bar, the pressure regulator has no
current and is open.
3. The rail pressure is 1800 bar, 100 bar from the spring and 1700 bar from the energised coil.
Questions for students
1. Where is the pressure regulator located?
See answer
The pressure regulator is located on the high-pressure pump or on the common rail.
2. List the components of the pressure regulator.
See answer
Coil, anchor, spring, core, ball valve.
3. If the rail pressure becomes too high, what should be done with the pressure regulator?
See answer
The pressure regulator has to be opened further.
4. The pressure regulator is not activated. How high will the rail pressure be during starting?
☐ The pressure will depend on the rotational speed of the high-pressure pump.
☐ 300 bar.
☐ 0 bar
☐ 2000 bar.
☐ The maximum pressure that corresponds to the force of the spring.
See answer
☑ The maximum pressure that corresponds to the force of the spring.
5. How does the engine control unit change the rail pressure with the pressure regulator?
See answer
The engine control unit regulates the rail pressure by controlling the current through the pressure regulator. The higher the current, the higher the rail pressure.
As an introductory teaching resource, this article helps teachers explain the basics of pressure regulation in Common Rail Diesel (CRD) systems and assess students’ understanding before progressing to more advanced instruction.
For educators looking to expand their lessons further, Electude offers a wide range of digital learning solutions and teaching materials for automotive training. Explore our heavy vehicle curriculum to discover all the topics available.
