ALEX LPG / How do car gas systems work?

LPG systems

How does a car gas system work?

See how the LPG system in your car actually works. Introducing a safe, modern and intelligent way to run your car on liquefied petroleum gas.
  • Switch
  • Tank
  • Multi-valve
  • Gas inlet
  • Reducer
  • Vapour phase gas filter
  • Mapsensor
  • Gas injectors
  • LPG controller
An autogas system step by step
Switch Switch
Tank Tank
Multi-valve Multi-valve
Gas inlet Gas inlet
Reducer Reducer
Vapour phase gas filter Vapour phase gas filter
Mapsensor Mapsensor
Gas injectors Gas injectors
LPG controller LPG controller

Shows the gas level in the tank. It also features a  button that allows you to select the fuel type used by the engine.


A  fuel tank where liquid gas is stored. It is usually mounted in the spare wheel housing or suspended under the car (in the case of toroidal tanks). On the other hand, cylinder-shaped tanks are typically mounted inside the boot. Some vehicles have more than one tank installed.


It is an essential tank component that controls the gas fueling process and the proper gas flow to downstream parts of the system. Includes 7 mini-valves, i.e. an electromagnetic valve, pressure relief device, non-return valve, 80% filling limiter, excess flow valve, pressure relief valve and manual service valve.

Gas inlet
Gas inlet

Gas inlet with a  non-return valve – it is usually found under the fuel tank flap, right next to the petrol filler.


Reducer with an integrated gas valve. Otherwise known as an evaporator. It performs two tasks, i.e. heating the liquid gas to turn it into vapour and maintaining the appropriate gas pressure during engine operation.

Vapour phase gas filter
Vapour phase gas filter

Eliminates contaminants and centrifuges the gas to eliminate oil fractions. It is mounted before the gas injectors.


Measures the temperature and pressure of the gas stream. It feeds this data to the controller so that the latter can set the correct operating parameters for the injectors.

Gas injectors
Gas injectors

They inject precisely calculated doses of gas into the intake manifold channels. Gas injectors are installed either individually or in the form of the so-called injection rails.

LPG controller
LPG controller

A  sophisticated computer that controls and monitors the operation of all system components.

An autogas system step by step

  1. The first step is to fill the tank with autogas. The fuel stored in the tank starts to travel towards the engine once the latter has been started. A  multivalve opens at the very start and feeds liquid LPG into gas distributor under high pressure.
  2. Fuel flows through an LPG solenoid valve, and once it has been pre-cleaned, to the regulator. At this stage, the gas evaporates and its pressure is reduced to about 2 bar.
  3. Though already in the vapour phase, the gas does not slow down and goes to the vapour phase filter for the next stage of contaminant removal.
  4. The mapsensor measures the pressure of the gas fed to the injectors and the negative pressure generated in the intake system. It then passes this data to the controller, which corrects accordingly and selects the appropriate gas injection timing.
  5. Afterwards, the clean and ready-to-combust gas goes directly to the LPG injectors, then to the intake manifold (separately to each intake channel), and finally to the engine combustion chambers. The timing of feeding the gas to the intake manifold’s individual channels is identical to the sequence of engine operation on petrol.
  6. This complex operation is managed by a  sophisticated computer – the controller. It controls the electromagnetic valves , monitors the gas parameters (temperature and pressure) and determines the injector opening/closing times (which can be different for each cylinder).
  7. Finally, it also ensures smooth switching between fuel types upon pressing the petrol/gas button located on the car’s dashboard control panel – the final component of the system. What is the result? Click the button and drive on autogas.

Smart technologies by ALEX

The gas is managed by intelligent electronics included in the gas system components every step of the way from the tank to the engine.

Sometimes when you accelerate while the engine is still cold, the fuel type immediately switches from gas to petrol. Surely you already know it is no accident. This happens when the engine receives too large a  dose of cold fuel. This is detected by the reducer, which is equipped with a  housing temperature sensor. It immediately sends a signal to the controller, which reacts by switching the fuel type to petrol. Only once the engine reaches the right temperature will the controller switch the system back to using gas.

It is worth noting that despite the engine start process automatically using petrol by default, all ALEX systems also feature an emergency start function that allows you to start your engine using gas in case of a  failure in the petrol system.


Did you know that the multivalve OCTOPUS consists of as many as 7 mini-valves? It is these valves that ensure the safe operation of your LPG system.

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
1. 80% filling  limiter

The first one is an 80% filling limiter, which leaves a  20% air buffer in the tank.

2. Pressure relief valve

The pressure relief valve protects the system against excessive pressure build-up.

3. Pressure relief device

The pressure relief device activates at temperatures above 110oC.

4. Electromagnetic operating valve

It opens when the engine starts and closes once the engine stops running.

5. Excess flow valve

It protects the system against an excessive gas flow exceeding the engine’s requirements.

6. Non-return valve

It ensures that LPG fuel flows only towards the gas tank during refueling.

7. Manual service valve

It is primarily used for maintenance work, e.g. filter replacement.

8. Fuel level indicator

Allows you to easily check the tank fill level.

A safe and proven system

Fourth-generation LPG systems are safe and smart solutions.

They have been refined to perfection over time, ensuring their technological maturity, and feature advanced electronics, thoroughly tested components and the finest materials available. Despite the existence of next-generation LPG systems, the most commonly installed LPG systems in the world are still the sequential autogas injection systems. They provide:

  • precise gas dosing that corresponds to the current demand of the engine – it allows to limit any losses and increase savings,
  • matching to gasoline engines, which makes the entire system trouble-free – provided that its components are correctly selected and assembled,
  • no influence on the operation of the on-board diagnostics system, car power, and engine wear.

In addition, the system guarantees automatic and smooth switching from petrol to gas when there are appropriate conditions for this operation – reaching the appropriate reducer temperature and gas pressure. IV generation LPG installations have no disadvantages, unlike older systems – they only require refueling at trusted stations and adherence to periodic inspection dates.

Why is it worth choosing the installation of the 4th generation LPG installation?

The 4th generation installations are fully developed and guarantee failure-free engine operation – regardless of the conditions. They allow you to save money on a daily basis while driving, and they only require professional assembly and components from reliable manufacturers. Properly installed LPG car system can be used also as an alternative power supply option in the event of an emergency. The installation of the system itself pays for itself faster the more kilometers you travel. In most cases, this is a maximum of one year.

We encourage you to familiarize yourself with the offer of the manufacturer of modern gas installation systems ALEX LPG. If you need additional information, please contact the brand consultants who will be happy to dispel any doubts.