LPG reducer for LPG systems

LPG reducers – function, symptoms and repair

How does an LPG reducer work?

An LPG reducer is one of the most important components of an LPG autogas system. Its task is to convert the cold LPG from the tank from the liquid phase into gas form and at the same time reduce the pressure from approx. 10 bar to 1–2 bar working pressure. The LPG autogas reducer is also referred to as a pressure reducer and is necessary to reduce the pressure and safely supply the autogas to the engine via the LPG injectors.

To carry out this process, it requires energy in the form of heat, which is provided by the engine’s waste heat via the coolant. For this reason, the LPG reducer can also be seen as a heat exchanger.

Reducers in LPG gas systems usually have a two-chamber system separated by a rubber diaphragm. The LPG reducer is connected to the vehicle’s coolant circuit in order to bring the reducer up to temperature using the warm coolant. Liquid LPG flows through the second chamber, where it is heated, vaporised and converted into the gas phase. The reducer requires a specific working pressure, which can be adjusted on most reducers using a regulating screw.

The most important thing to know about the reducer is that it must always be completely sealed and should not have any leaks. Otherwise, the required working pressure cannot be maintained. If the rubber diaphragm is leaking, the autogas fuel could mix with the coolant and, in the worst case, this could lead to engine damage.

Reducers for gas systems usually have a kW rating, which is based on the engine power of the vehicle being converted. The kW rating of the autogas reducer should be understood as the upper limit in order to ensure long-term and safe vehicle operation.

The most widely used LPG reducers include Prins reducers, BRC reducers, KME, Landi Renzo, Zavoli, Lovato, Tartarini and others.

With repair kits, high-quality reducers from Prins, BRC, Landi Renzo and other manufacturers can be repaired cost-effectively. Repairs should always be carried out by a qualified specialist.

Symptoms of a defective LPG reducer

A defective reducer often has various causes, including poor gas quality, which can cause the reducer to become sticky or clogged, incorrect installation or a defective rubber diaphragm.

Since the reducer must constantly maintain a specific operating pressure for safe operation, problems such as contamination, sticking or leakage can cause the LPG reducer to no longer maintain its working pressure consistently. Depending on the problem, the reducer pressure rises or falls, which can cause the gas system to shut down and the vehicle to switch back to petrol operation. The gas control unit controls the switch back to petrol operation.

A special feature of Prins gas systems is that, in the event of reducer problems, a 10-minute lockout is activated when switching back to petrol operation. This prevents the driver from switching the vehicle back to gas operation. When the 10-minute lockout has expired and an attempt is made to switch the vehicle back to gas operation, but the reducer pressure is still too high or too low, the same fault message becomes active again and the 10-minute lockout is triggered again. This makes it possible to narrow down reducer problems very well by remote diagnosis in Prins gas systems.

First-generation Prins reducers, which were equipped with two diaphragms, often had the problem that gas entered the coolant circuit when the reducer was defective. This was very dangerous for the engine, as gas at approx. 10 bar pressure entered the coolant circuit, which operates at approx. 2 bar. When troubleshooting why the pressure in the coolant circuit had increased, it was often not apparent that the reducer was the cause of the problem. As a result, the cylinder head gasket was often replaced at high cost without eliminating the actual cause.

These problems no longer occurred with newer generations of Prins reducers with a modified design.

If a defective reducer is suspected, the cap of the expansion tank can be opened to check whether a smell of gas is noticeable.

Sticking of the reducer due to poor gas quality

Poor gas quality can cause deposits to form inside the LPG reducer, which in turn can cause it to stick. A sticky reducer can no longer be regulated and can no longer maintain constant pressure. As a result, the LPG gas system switches back to petrol operation.

In any case, the reducer must be checked by a qualified specialist to ensure that it is functioning properly. Either the reducer must be replaced, or its internal components can be fully overhauled using a repair kit.

Reducer problems caused by installation errors

Incorrect installation of the LPG reducer is a common cause of problems with the LPG autogas system. It must be properly integrated into the coolant circuit so that it reaches a sufficiently high temperature, approx. 70–90 degrees Celsius or higher, in order to convert the liquid autogas into the low-pressure gas phase. If the reducer is not installed correctly, it may not reach the required temperature. This can, for example, result in excessive reducer pressure, causing the gas control unit to switch the system back to petrol operation.