Flexible LPG Hoses (LPG Pipes)
Rubber hoses (flexible LPG pipes) are most commonly used in automotive LPG systems to connect components that may move slightly relative to each other. Their flexibility ensures a tight seal even when such movement occurs.
LPG Hoses in the Low-Pressure Section of the Gas System
Connections made with flexible rubber hoses (LPG pipes) are used in the low-pressure part of 4th-generation automotive LPG systems (sequential injection systems), where the LPG is already in the vapor phase (after evaporation, which occurs in the pressure reducer/vaporizer).
Flexible Hoses – LPG Pipes
Flexible LPG hoses (LPG pipes, rubber hoses – made of special rubber compounds) are therefore used in connections between the reducer/vaporizer, the vapor-phase filter, and the gas injector rail. These are all components that can move slightly relative to one another.
The reducer/vaporizer is mounted to the car body, while the gas injector rail is attached to the engine, which moves slightly relative to the body (due to vibrations at idle or load changes while driving). The vapor-phase filter located between these components may be freely positioned on the LPG hose or mounted to the car body as well.
Injector Hoses
Another use for rubber hoses (small hoses) is to connect injectors with the nozzles screwed into individual intake manifold channels, through which the vapor-phase LPG is delivered to the engine.
Homologation
Flexible LPG hoses are specifically designed for use in automotive gas installations and must be approved according to UN Regulation No. 67, which defines the specific working conditions they must meet, including pressure (up to 4.5 bar) and temperature range (from -25°C to +125°C).
Other Properties of LPG Hoses
LPG hoses must have a defined tensile strength and elongation capacity, both of which are specified by relevant standards.
In addition, LPG hoses must demonstrate adequate resistance to bending and, of course, tightness. The leak test is performed after the bending test.
Construction of Flexible LPG Hoses
A flexible hose (LPG hose) consists of an inner layer and an outer cover (sheath), which must be reinforced. This reinforcement allows the hose to bend without changing its internal diameter and provides the necessary strength to withstand internal pressure.
The inner layer must be made of a material (rubber) resistant to the effects of LPG. The outer layer (sheath) must be resistant to high temperatures, oils, and other operating fluids, while also providing mechanical protection for the hose.
Materials Used in LPG Hoses
LPG hoses are made from various rubber compounds based on synthetic rubbers, with specific additive packages that give them desired properties and resistance to certain factors.
The use of appropriate materials in LPG hose construction does not mean they are maintenance-free. Over time, they may degrade during operation. Loss of elasticity can lead to leaks, which can affect the safety of the LPG system. For this reason, LPG hoses used in gas supply systems should be periodically replaced with new ones. There is no fixed replacement interval since the wear rate depends on their quality and operating conditions. The correct assessment of LPG hose condition should be carried out by a workshop specializing in LPG system servicing, and their recommendations should be followed.