Written by Eric Hahn
POL Valve & Cylinder Confusion
All LPG gas cylinders have some form of gas valve.
LPG users in Australia will see numerous references to POL valves and POL cylinders but what exactly is a POL valve?
What are POL Gas Valves and Cylinders?
• POL refers to a type of gas valve and to gas bottles that have a POL valve fitted.
• "POL" is an acronym for the company that first made the valves — Prest-O-Lite.
• POL is the most common type of valve & cylinder, in Australia, for most LPG gas cylinders from 4kg to 210kg.
• The POL connection is notable for its reverse — left-handed — thread.
• A pressure relief valve is incorporated within the POL valve for safety.
There are a few more features of the POL valve of which you should be aware...
Gas Line Connection
The gas line pigtail or regulator screws into the large female threaded opening on the side of the valve.
It is unique in that it has a left-handed or reverse thread. So, to tighten it, you turn the connector anti-clockwise.
Tightening is achieved either with a wrench or by turning a hand wheel.
You should always do a soapy water leak test after every reconnection.
Gas Connection Seal
The POL valve was originally designed as a metal to metal compression seal.
However, some connectors are now manufactured with rubber O-rings to further improve the seal.
The downside is that these can become damaged or deteriorate over time so they should be checked regularly.
Gas Valve Hand Wheel
Located on the top of the POL valve, the gas valve hand wheel controls the flow of gas, once the connection is secure.
Turning the hand wheel anti-clockwise starts the flow of gas but you should avoid turning it hard to the open stop.
Opening the valve 2 or 3 turns is all you need.
You shut the gas off by turning the hand wheel clockwise, tightening firmly by hand only.
CAUTION: Never open the valve when unattached
POL valves are equipped with a bleed screw for decant filling, such as when having a BBQ bottle filled at a service station.
It is a small slotted screw on the side of the valve.
The filling technician opens the screw during filling to determine proper filling.
On the other hand, most large gas depots fill cylinders by weight, on digital scales, so the bleed screw is not used.
CAUTION: Never open the bleed screw on your gas valve
The valve has a tube that sticks down into the cylinder, called a 'dip tube'.
It extends down to the bottom of the ullage area.
This tube is connected to the bleed screw and let's the filling technician know when the cylinder is filled up to the the ullage zone.
Ullage is the 20% unfilled space at he top of the gas cylinder that allows for expansion of the gas.
Pressure Relief Valve
The pressure relief valve is the single most critical safety feature on an LPG cylinder.
It is incorporated within the POL valve and appears as the protrusion opposite the main connection.
It usually incorporates some kind of plastic dust cover that should be left in place.
Pressure relief valves are designed to relieve excess pressure that might result from overfilling or exposure to excessive heat or fire.
The function of a pressure relief valve is to keep a cylinder from rupturing in the unlikely event of excessive pressure build-up.
The pressure relief valves are held in the closed position by the force of a powerful spring inside.
As long as the pressure is less than that of the spring, the valve will remain closed.
Having the pressure relief valve releasing gas is a rare event.
Most people will never experience venting.
If the pressure rises beyond the force of the spring, the valve will open to vent the excess pressure.
If this happens, you may hear a hissing sound and see cold gas vapour being released.
Once sufficient pressure is released, the valve closes.
If this ever happens, just stay clear of the area and let the gas dissipate.
You should also call your LPG supplier, from a safe location, and advise them that your gas cylinder is venting gas.
Do not use your mobile phone, any electrical devices or other ignition sources near a venting gas cylinder.
BBQ Gas Leak Test
It is important to regularly leak test your BBQ gas bottle, regulator and hose.
Leaks from these items are frequently the cause of BBQ gas fires.
How to Test
Put some soapy water in a spray bottle.
Turn on the gas bottle without turning on the BBQ.
Next, spray the entire valve, regulator and hose assembly with the soapy water.
Bubbles will form if there is a gas leak and you may also smell the gas.
For more details, please see: BBQ Gas Leak Test
Hot To Safely Attach or Change Your BBQ Gas Bottle
Connecting & Disconnecting
The male connector of a POL regulator has a reverse or left-handed thread.
So, to detach, you turn it clockwise and then anti-clockwise to re-attach.
Full step-by-step instructions:
How to Attach or Change Your BBQ Gas Bottle
View More LPG Gas Blogs
Comments, questions or feedback?
The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.