Any proof that water in air cylinder is bad?

[Chris Bauer]

I have Steyr LP10. I fill up the cylinder with hand pump.

I don't see any mention of bleeding out water after pumping in the Steyr manual.

But there is perceived notion in this forum that water need to be bled out from the cylinder.

In the past, after pumping up the cylinder, I would turn the cylinder a small turn, bleed out a quick puff from the pump bleed off knob, then pump a more times to get the pressure back up.

I wonder if this bleeding off water is really necessary.

My friend who is an air rifle shooter said he has two hand pumps. One with water filter, the other does not. He said it makes no difference whether he filters out water or not in his cylinder. They are just as accurate. I think air rifle is more finicky than air pistol.

So is bleeding off water from air cylinder a myth? I am tired of bleeding off my "hard earned" pressure to drive off water.

So what if I am driving off the water? So what if I am not driving off the water?

[Tom Amlie]

He said it makes no difference whether he filters out water or not in his cylinder. They are just as accurate. I think air rifle is more finicky than air pistol.

Accuracy isn't the issue...rust is. When you've got that cylinder up to 3,000 PSI that last thing you want is corrosion inside, weakening the cylinder. You'll never know the corrosion is there unless/until the thing blows up.

Is it a common occurrence? No. Has it ever happened? I don't know. Do I want to be the one to find out? No way.

[TomAmlie]

I should have logged in before so I could edit my posts if needed...my apologies for cluttering things up.

I've always assumed that rust was the issue, but is that a correct assumption? What are the cylinders made of? Stainless?

[Chris Bauer]

Cylinders are made of aluminum.

I don't see the Steyr manual saying anything about purging the water. Water will be purged automatically during discharge. So if water does not affect accuracy, and there is no proof that it actually cause corrosion, why purge?

[jipe]

The issue is indeed corrosion. Not so much in the cylinder (most are made of aluminium now but it is not the case of all of them, I think that the 300bar Walther are steel) but well in the pistol especially the regulator.

Is it a real issue ?

I also tried to find information and never could get any coherent answer, the information I got are contradictory:
- some gunshop say that it is very important to avoid moisture in the cylinders and you should use dry air.
- as many others say that it is not an issue.
- when I asked the Steyr importer in my country and the gunshops if they ever had to repair a pistol due to corrosion problems, they said they never had any return due to corrosion.
- Steyr list the hand pump in the methods allowed to refill the cylinder without saying anything about moisture.
- Anschutz says in the LP@ manual that dry air should be used but without saying anything about the use of hand pump.
- some pumps have a system to remove moisture, some other not. Compressors dedicated to refill PCP gun have a moisture removal system.
- I have used an hand pump for my previous LP10 who served me during many years (bought end 1999). I tried to purge after each refill but never had any water coming out.
- when I bought a second LP10 I decided not to use the hand pump for that one "just in case"

Hopes it helps !

[RobStubbs]

I think this thread has been done before but just to add a few points. Water causes corrosion of numerous metals including aluminium. I'm lead to believe you can tell the method of filling by examining the inside of cylinders as the pumps produce a lot of water (I drain my pump when I use it - which is rarely as I have a dive cylinder - but you do get water dripping out). Has water corrosion led to failures of cylinders or guns, I seem to recall it has of guns but I can't confirm that and don't know about cylinders.

Rob.

[Denis]

Chris
I'll be a little blunt here.
If you want to gamble with water in your cylinders causing corrosion that will cause eventual failure, go ahead.
Just think of your shooting buddies, or a family member that may be around when it eventually goes.
Moisture and metals/aluminiums don't mix well.
Check with any Aircraft Repair facility.

[Chris Bauer]

Frauke Umdasch, chief technical adviser at Steyr-sportwaffen, replied my question as such:

"you need to bleed off the water from the pump, NOT from the air cylinder. As long as there is never too much water in the pump, there won’t be any water in the air cylinder. If you forget to bleed off the water from the pump, there might get water into the air cylinder and further on into the mechanic of the weapon, which will cause damage, as you can imagine!"

Now I am a bit confused, how do I bleed off water from the pump? I am sure I was bleeding off from the air cylinder and not the pump.

[RobStubbs]

Now I am a bit confused, how do I bleed off water from the pump? I am sure I was bleeding off from the air cylinder and not the pump.

Very easy, you just unscrew the nut underneath the connector that you screw in the cylinder to. On my pump it's just a round knurled nut. I leave this unscrewed most of the time, just to let the pump dry out. And as I said above, you do get a fair bit of water coming out if you don't do it every single time (especially in a moist <humid> environment).

Rob.

[john bickar]

Very easy, you just unscrew the nut underneath the connector that you screw in the cylinder to. On my pump it's just a round knurled nut. I leave this unscrewed most of the time, just to let the pump dry out. And as I said above, you do get a fair bit of water coming out if you don't do it every single time (especially in a moist <humid> environment).

Rob.

Now I'm confused. How do I unscrew the loose nut behind the trigger?

[RobStubbs]

Now I'm confused. How do I unscrew the loose nut behind the trigger?

Don't worry mate, it's already unscrewed more than enough ;)

Rob.

[jacques b gros]

Solved the problem in our club: rented a bottle of 50 liters of Nitrogen at 200 bar.

Cheapest gas (is the first that comes out of the air, since is ~80% of it), cheaper that breathable air, 99.9999% pure and moisture very near absolute zero.

Besides, does not reacts with any substance. I'm no chemist, but should be healthier to the gun.

[RobStubbs]

Besides, does not reacts with any substance. I'm no chemist, but should be healthier to the gun.

Except with the minor issue that the gun and regulator etc was designed for air and not nitrogen. It may therefore behave differently and fire at a different velocity.

Rob.

[jacques b gros]

The compressed air is (more or less) 80% Nitro, 17.8 Ox and the rest is...the rest. Moisture included.

Doubt that this would make any appreciable difference, specially since N is an inert gas.

Might be better...

[RobStubbs]

The compressed air is (more or less) 80% Nitro, 17.8 Ox and the rest is...the rest. Moisture included.

Doubt that this would make any appreciable difference, specially since N is an inert gas.

Might be better...

Thanks for the chemistry lesson, but you 're missing the point. The guns are designed and set up with a different gas than the one you are using - yes we all know air is mainly N2 but it's the bits that aren't that matter. Also compressed air requires no treatment, other than drying, so is cheaper and far easier to get than N2.

Feel free to use whatever you fancy, but I'll stick with compressed air as recommended by the gun makers, especially since I can get a dive bottle filled in about 5 different shops within 10 miles of home for the cost of a pint of beer.

Rob.

[Chris Bauer]

I am a little bit confused here.

I don't understand my physics well here.

pv=nrt pump pressure in, same volume, temperature go up. As temperature drop down to room temperature, water condensation occurs.

By all recommendation in this forum, I am bleeding water off from pump, not the air cylinder. But doesn't water condensation occur inside the cylinder? Once I take the cylinder off pump, pump pressure drops to zero, so where does water come from?

[jacques b gros]

Rob,

At least this part,

" Also compressed air requires no treatment, other than drying, so is cheaper and far easier to get than N2."

is not true everywhere. I live in a city some 300 mi from the nearest decent diving spot. The is one dive shop in town, plus a friend who is a professional diver. So, maybe three publicly available compressors in town.

If I want to fill my scuba (7 liters) to 200 bar, I'll pay some US$30. Have to carry it and pick it up next day. To fill the N2 tank, with 50 liters, I pay 50 dollars, and the truck arrives, if not late in the afternoon, in half an hour.

[David Levene]

But doesn't water condensation occur inside the cylinder?

As I understand it, not if you are putting dry air in.

Some will remember that before Steyr started fitting dial gauges to their cylinders they had a "pop-out" indicator to give an idea of how much air was left.

That indicator included steel springs.

Watching the Steyr service agent strip the cylinders for servicing it was obvious which ones had been filled by pump. They were the ones with rusty springs.

[Roboptic]

When oxygen is compressed- by foot pump or compressor- the excess moisture needs to be removed. This is done for mechanical reliability reasons to avoid corrosion and rust . In fact when diving on an open circuit system there is a constant problem with dehydration of the divers.
When transferring compressed air from dive bottle to AP cylinder you are not recompressing the air so there should be no new moisture.
These are not absolutes but they are within the technical specs of what is acceptable for diving and PCP gear.
" I am not an engineer, I just play one in my garage"

[jipe]

There are also springs in the regulator that might suffer from moisture.

There is no doubt that using a hand pump will introduce some moisture. There are hand pump with a moisture removal system, but how effective are these ?

Comptressors also have a moisture removal system including the one used for filling diving tanks because many diving tanks are made of steel and suffer from corrosion. Inspection to detect corrosion is part of the process to (re)certify diving tanks.

There is also no doubt that moisture will cause some corrosion and that ideally, it should be avoided.

The question I still have is if in practice corrosion causes failure for AP ? Till now, I never met anybody (shooter or gunshop or even importer) who experience AP failure due to corrosion. PCP is on the market since about 10 years, may be this is not long enough to have corrosion failure ?

Then may be one remark about tanks to refill AP cylinders: 5 or 7l tanks should be avoided if possible since their small volume makes that the pressure drops fast and then the number of shots possible per AP cylinders also drops fast.

10l or even 20l is much better since you can do a decent to large amount of AP cylinder refill before the pressure drops enough to really reduce the number of shots per cylinder. In most diving shops the price to refill a 10l is the same as for a 5l or 7l. It is sligthly more expensive for a 20l andt much than the double (i.e. two refill of a 10l).

The price difference between 7l and 20l is not that much too. What is much more expensive is 300bar tanks, whatever the capacity.

The only problem with 20l is the weight, 10l are not that much heavier than 7l. So I would say, use 5l is you have to often carry the tank with you, otherwise go for at least 10l and if you are strong enough go for 20l.