Understanding the Pressure of LPG Cylinders and Its State

Liquefied Petroleum Gas (LPG) cylinders are essential in both residential and commercial settings, providing a reliable source of energy. This article aims to clarify the pressure conditions inside an LPG cylinder and the phase state of LPG within it. The topics include the typical pressure range, the liquid and vapor states of LPG, and the safe filling limits of LPG cylinders.

LPG Pressure and State Explained

LPG is typically stored in cylinders under pressure to maintain its liquid state. The internal pressure of an LPG cylinder varies based on various factors such as temperature and the composition of the gas. Generally, the pressure can range from around 7 to 8 bar (100 to 116 psi) at room temperature, approximately 20°C or 68°F.

The internal state of LPG within a cylinder is characterized by two phases:

Liquid Phase: The majority of the LPG is in a liquid state due to the high pressure in the cylinder. Vapor Phase: Above the liquid, there is a vapor space where the LPG is in gas form. When the valve is opened, the liquid LPG vaporizes and is released as gas for use.

As the pressure in the cylinder decreases due to the use of gas, some of the liquid will evaporate to maintain the pressure until the liquid is depleted.

The Safe Filling Limit of LPG

The LPG is filled in cylinders in a liquid state up to 85% of the volume, considering the evaporation of LPG to vapor. After filling, the cylinder will maintain a safe equilibrium pressure, which is typically around 5.5 bar (80 psi) at room temperature.

An interesting fact is that adding vapor to the filling process can save space in the cylinder, reducing its weight. The equilibrium pressure in a gas cylinder depends on the surrounding temperature and can vary from 5.5 bar to 6.5 bar depending on the cylinder's design and the temperature at which it is stored.

Evaporation and Equilibrium Pressure

The pressure at which LPG becomes a liquid is its vapor pressure. This pressure varies depending on the composition and temperature of the gas. For example, pure butane has a vapor pressure of approximately 220 kilopascals (32 psi) at 20°C (68°F), while pure propane has a vapor pressure of approximately 2200 kilopascals (320 psi) at 55°C (131°F).

Key Insights:

The pressure in an LPG cylinder can vary from 5.5 bar to 7.0 bar, depending on the cylinder's storage temperature. The equilibrium pressure in LPG cylinders depends on the surrounding temperature and can vary between 5.5 bar to 6.5 bar. The safe filling limit for LPG cylinders is 85% of the cylinder's volume, considering evaporation, up to a maximum pressure of 80 psi.

Understanding these key aspects of LPG cylinder pressure and state is crucial for safe handling and usage, ensuring reliable energy supply and safety in both domestic and commercial settings.