ELGAS Knowledge Hub

How is an LPG cylinder refilled?

23 Jun, 2023 | Business LPG, Residential LPG

In this article:

Why LPG cylinders should only be refilled by trained professionals and what are the involved steps.
Refilling LPG cylinder

Two approaches

You can fill a gas cylinder in two ways – LPG gas cylinder refill (fill propane tank) by weight or LPG gas cylinder refill by decanting until it starts to vent gas.

LPG gas cylinder refill by weight involves inputting the tare weight (empty cylinder weight) and the desired amount of gas to be filled into a digital scale.

The other method to fill a gas cylinder is referred to as ‘decanting’, which is how LPG gas cylinder refill is typically done at service stations.

When doing LPG gas cylinder refill by weight, the filling hose is controlled by the scale, which shuts it off when the appropriate weight is achieved.

To refill LPG gas cylinder by decanting, a small vent screw is opened which allows gas to vent when the gas inside the cylinder reaches the full refill level. The venting gas is the operator’s cue to stop the LPG gas cylinder refill and close both the vent screw and main valve.

See – VIDEO (Disclaimer: This video on How to Fill a Gas cylinder is only a supplement and refresher for trained individuals and professionals. LPG decanting must not be attempted by untrained individuals.)

Current Inspection Date Required to Fill Gas

No matter which of the LPG gas cylinder refill methods are used, the cylinder must have a current inspection date. It is the responsibility of the refill technician to check the inspection date stamped into the neck ring of the gas cylinder before refill takes place.

Out-of-date gas cylinders cannot be refilled until they are re-inspected and stamped with a new inspection date.

How to Fill a Gas Cylinder Refill Using Digital Scales

Using digital scales helps ensure proper and safe refill LPG gas cylinder , based on weight. When the total weight equals the empty weight plus the appropriate LPG gas cylinder refill weight, the gas cylinder refill is complete.

The scales are set for each individual refill LPG gas cylinder, based on its empty (tare) weight, as well as the desired LPG gas cylinder refill content weight, when full.

How the Scales Work

The tare weight (empty weight) is stamped into the neck ring by the cylinder manufacturer. The operator inputs the tare weight of the gas cylinder into the scale’s keypad. After inputting the weight, to fill a gas cylinder, the technician connects it to the LPG supply. The refill LPG gas cylinder is automatically stopped by the digital scale, after reaching the target weight. This ensures a very accurate gas cylinder refill and avoids dangerous overfilling or lost value through under filling.

Faster Way to Fill a Gas Cylinder with Carousels

A side benefit of using scales to fill a gas cylinder is speed. The LPG supply line can be pump driven for to fill a gas cylinder faster. This is not possible with decanting, as the operator might be too slow to stop the gas cylinder refill process, resulting in dangerous overfilling.

Digital scales and pump driven LPG also allow for the use of high speed carousels to fill gas cylinders, like the SWAP’n’GO carousel in the accompanying image.

In fully automated plants, with gas cylinder refill carousels, even the keypad step can be automated. The carousel digitally reads an RFID chip on the cylinder that contains the tare weight, as well as the rest of the manufacturing specifications of the gas cylinder.


Decanting Method to Refill LPG Gas Cylinder

To transfer LPG gas from one cylinder to another, technicians use the decanting method. Decanting is the process use are petrol stations. After connecting the gas cylinder to a larger LPG storage tank, the trained operator begins to fill a gas cylinder until some gas starts leaking out of the loosened bleed screw. The operator is supposed to stop refill LPG gas cylinder as soon as liquid LPG starts coming out of the bleeder opening. The liquid LPG escaping is unmistakable, as it looks like a white cloud.

This intentional venting of gas into the atmosphere, during the refill LPG gas cylinder, is avoided with the digital scale method.

Decanting can also result in either over filling or under refill LPG gas cylinder, as well as correct refill LPG gas cylinder, depending on the gas cylinder and the operator filling it.

For example, if the operator is slow to stop the gas cylinder refill when the liquid LPG starts to bleed out, the gas cylinder could easily become overfilled (which is very hazardous).

20% Oversized for Expansion

LPG vapour pressure rises with temperature.

If a gas cylinder is exposed to higher temperatures, the gas will expand.

LPG cylinders are designed to be full while allowing 20% of the space, called “ullage”, for the natural expansion of the LPG.

Properly filled gas cylinders, with the required 20% ullage, should never have a problem.

Overfilling is Unsafe

When over filled, a gas cylinder has less than 20% ullage, creating the possibility of the unwanted release of gas to the atmosphere, through the pressure relief valve.

The pressure relief valve is incorporated into the main gas valve on the cylinder.

It’s a valve within a valve that prevents dangerous overpressure situations.

So, overfilling combined with heat can result in gas venting from the pressure relief valve, which creates a significant safety hazard.

This is especially true in the warm Australian climate.

LPG refilling is NOT a DIY Procedure

Only trained technicians should attempt to fill a gas cylinder by either method. LPG gas cylinder refill is not a do-it-yourself handyman procedure and should never be attempted by untrained personnel.

The trained operators know all about the appropriate procedures, what personal protective equipment (PPE) to wear, the importance of the proper type of clothing (including material), proper cylinder grounding, static electricity hazards, ignition sources, fire protection and more.

In-depth safety training is mandatory for these technicians.

Doing it incorrectly could result in cold burns (liquid LPG is -42°C), fire or even an explosion, in addition to dangerous over filling of a gas cylinder.

The simple message for people who are thinking about trying to refill their own gas cylinder -just DON’T do it!


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