BACK TO BASICS
This month Neil Price talks us through pre-charged pneumatic cylinder pressure
Neil Price explains the safety aspects of PCP cylinder pressure, and how to take basic precautions
Any air-pressured vessel can be extremely dangerous if not treated in the correct manner. They are basically pipe bombs that can explode when mistreated, so the greatest care must be taken when doing anything with a pre- charged pneumatic gun’s air pressure cylinder.
The first and most important thing is the fill pressure. Most cylinders have it stamped on them, and handbooks state categorically that the MAXIMUM fill pressure is 200 bar on many guns, although this does vary from manufacturer to manufacturer. That is almost 3000 pounds per square inch of pressure. Now then, as stated, that is a maximum fill pressure, it is not a target pressure that you have to achieve, exactly the same as speed limits on our roads. It is a figure that you are allowed to go up to, but not go over.
When filling pre- charged pneumatic airgun cylinders, always go on the pressure indicated gauge on the high-pressure tank that you are filling from. These are usually much more accurate than the small manometers that are fitted to airguns.
I have found that when filled to the maximum pressure, guns are not as accurate as they should be until the pressure in the air cylinder has dropped by about 20 bar, so I only fill my guns to 180 bar and I find that the accuracy is there for me from the first shot.
In the past, I had a rifle brought to me, which was ‘ leaking’. It was an Air Arms S400 and as I examined it, I found that one end of the air cylinder was like the bottom of a bell with the whole periphery blown out. The owner swore black was white to me that he had never filled it over 200 bar. Needless to say, I accepted that statement with a large pinch of salt.
It is very important that you only fill the air cylinder of an airgun with clean, dry compressed air. NO OTHER GASES ARE EVER TO BE USED. Using other gases has caused accidents in the past that have led to some nasty injuries, so please heed this warning.
When fitting the adaptors into the neck valve of your 300 bar air tank, never use a spanner to tighten them into the aluminium threads. This is for two reasons; the excess force that can be applied with a spanner can damage the aluminium threads in the valve, and the ‘O’ ring on the sealing face will become completely flattened and its working life will be vastly shortened. Always tighten these into the valve by hand only, and then let the compression on the ‘O’ rings do the work. Also, regularly check the condition of the ‘O’ rings on the tank connector and the fill probes. If you have more than one pre- charged pneumatic gun that uses different fill probes, then a versatile fill system should be thought about. A very good source of these products is Best Fittings, a company that specialises in filling accessories for airguns and can be found at https://www. bestfittings.co.uk
When filling an air cylinder, always fill it as slowly as possible so then it will be easy to stop the fill at the precise required pressure, and so minimise the danger of over-filling. Most air tanks are now fitted with slow-release valves anyway, but some older tanks that you might buy second- or third-hand can have just open and shut valves. This means that the full tank pressure can be put into the air cylinder in a fraction of a second. That is why the fill knob should only be turned very slowly and under complete control, so that the air is transferred to the gun’s cylinder at a very slow rate. If a cylinder is accidentally over-filled, then dry fire the gun until the safe working pressure or below has been reached.
At the other end of the scale, do not let the pressure drop too low in the air cylinder. The most accepted minimum pressure for refilling is when 100 bar is reached, and no lower. For one thing, with too low an air pressure in the gun, accuracy suffers greatly, and secondly, pellets might not come out of the end of the barrel. If one gets stuck in the barrel then that usually can easily be cleared, but if the shooter does not realise that a pellet did not leave the barrel, then further shots might be taken getting more and more pellets stuck. The worst one that I have ever seen is when there were over 20 pellets stuck in a barrel. The only way to remove them was to melt them out with a gas torch on the outside of the barrel. The lesson here is to keep an eye on the gun’s pressure gauge, or be aware of the number of shots you have taken.
“that is a maximum fill pressure, it is not a target pressure that you have to achieve”
The gauge on your dive bottle will be more accurate than the one on the gun The maximum fill pressure is often written on the reservoir
Only ever use clean dry air in your PCP
This connection only needs to be hand-tight
If the pressure gets too low, pellets can get stuck in the barrel
Replace any ‘O’ rings that show signs of wear