by B.B. Pelletier
If you get into precharged airguns, sooner or later you’re going to get a scuba tank. You can get by with a hand pump for a long time. They do the job as long as you are willing to do the work. One day you’ll see somebody fill his Big Bore 909S from a tank in a handful of seconds after you just pumped yours for five minutes to get the next four shots ready, and you’ll decide that a scuba tank is not such a bad idea.
Two types of valves: DIN & K
There are two types of scuba tank valves for airgunners – the K valve and the DIN valve.
DIN valve: The DIN valve comes in two pressure ratings. Ten-meter target guns are mostly filled from DIN tanks because most 10-meter guns come from Germany where DIN is king. A DIN (Deutsches Institut für Normung) valve is characterized by female threads into which all attachments are screwed. Ten-meter guns come with brass adapters that fit the DIN valve and attach to the removable air tanks on the other side.
A DIN valve has a hole with threads to accept any devices. This is the deeper 300-bar DIN hole, though both have the same diameter and threads.
DIN valves come in both 200-bar and 300-bar ratings. One bar is about 14.5 psi, so you can do the math. The 300-bar DIN valve is just a deeper hole with more threads to effect a stronger grip on any attachment. Other than the length, the threads are the same for both DIN ratings. An O-ring on the face of every attachment seals the DIN-type valve interface when the attachment is screwed down flush against the flat bottom of the interior of the DIN valve.
K-valve: The K-valve uses some kind of clamp that surrounds the valve. A screw in the back of the clamp adjusts the tension between the clamp and valve. The valve has the O-ring, not the attachments, so this is something you should check frequently. If the O-ring falls out, you’ll never get a good seal.
The K-valve is flat with an O-ring to seal it. This type needs a clamp that fits around the back of the valve to hold it.
A refill clamp fits around the K-valve.
All sizes and pressure ratings!
Scuba tanks come in different sizes and pressure ratings. If your gun needs to be filled to 3,000 psi, your tank has to be able to be filled to that pressure, and this is where people sometimes get confused. A tiny tank can hold 3,000 psi air, but not very much of it. And a large tank may only be rated to 2,200 psi. It is the pressure rating that determines how much pressure can be put into a gun, and the volume of the tank determines how many fills you’ll get from it. A very common standard scuba tank that works for most precharged airguns is an aluminum 80 cu. ft., 3,000 psi tank. They cost $130 to $150 brand new and can be purchased used for under $100. Last week a friend of mine bought a used one for $35.
Tanks must be visually inspected every year
A dive shop will empty the tank and visually inspect it for signs of corrosion and work-hardening (from flexing due to pressure changes). Either problem can condem the tank – meaning that no dive shop will fill it for you. This is a risk you run when buying used. A visual usually costs around $10.
Hydrostatic testing every five years
A hydrostatic test determines whether the metal in the tank walls has work-hardened beyond specifications. For the test, the tank is pressurized well beyond its working pressure and the flexing of the outer circumference is measured. If it is still flexible, it passes its hydro and can be returned to service. A failed hydro means the tank can no longer be filled. Fortunately, the tanks that PCP shooters use seldom go below 2,000 psi before they are refilled, so the amount of work-hardening or fatigue they suffer is much less than what a scuba diver would subject it to by taking it all the way down to empty.
Carbon fiber tanks are the next thing
Carbon fiber tanks are lighter than scuba tanks and hold a greater volume of air. They’re what the rescue workers and firemen use when they can’t breath the air. One of these tanks is half the weight when filled and holds several times as much air as an aluminum 80 cu. ft. scuba tank. The big drawback is the cost, but some shooters need this kind of performance at any price. The other consideration is will you be able to get the tank filled to its 4,500 psi rating? Most dive shops won’t be able to fill that high, but a fire station can usually do it – so, do you have any friends there?
The BIG question!
You don’t have to be a diver or have a dive card to get a scuba tank filled. There is no law governing who can purchase high-pressure air, but dive shops need to be approached respectfully the first time you go, because they don’t HAVE to sell you anything! Take your refill clamp in and explain that you’re an airgunner and most dive shops will take it from there. Many will want you to sign a release promising you won’t breathe the air they sell you. That way, if you abuse their courtesy and wind up face-down in your swimming pool, they can show the six o’clock news that it was YOU who screwed up – not them.
If you want to get into PCP airguns, consider a scuba tank to be the same as the transformer for your electric trains. It’s not sexy and you don’t play with it, but it makes everything else work.
IMHO this Luxfer tank is the best deal in air available. 106cf at 4350psi is a lot of air!
Here is the URL: http://www.absolutescubadivingequipment.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=AS&Product_Code=ALW106&Category_Code=LUX
B.B.,
I agree 100% that a tank is the best way to go for shooting meets, etc., and I would dearly love to just turn a valve to fill my PCP tank but I have to repeat how much pumping up my tank contributes to my general health and vigor. I have checked into getting a tank, valve and refills at the local scuba store and so far just can’t justify the expense. The other advantage we Talon owners have is the large air tank which permits fewer refills for a given activity. I have promised myself, however, that I will get the apparatus for my 80th birthday! (If my wife will let me!)
CWI
What does the compressor cost that was covered a short time ago. Also can the tank compressor be used for other uses than air tank refills.
Earl Cox
What is the difference between the Webley Tempest and Hurricane other than the thirty dollar price?
Earl Cox
Earl,
The Tempest vs Hurricane will be a posting next week. There is a small difference.
B.B.
For the cost of the (very poorly rated FX compressor — about $1000) I can refill my tank at my local dive shop about 200 times. I use a 44cf 4500psi tank and refill about 1/month or so. In 10 years I would have paid for the compressor. If I had the Luxfer tank, my refills would probably drop to once-every-3-to-4-months (it holds a lot more air).
For the individual, a compressor makes no sense unless they are located a hundred of miles (or so) from the nearest refill station (or maybe 50 miles and it is limited to 3000psi).
Best,
Joe
Doc, If you want a tank of mine I may decided to take up an offer (I got today while filling up) for a 120CF 3500psi tank.
I have a 80FT 3000psi tank that’s about a year new and never been drawn down past 2800psi availabale. I’d be happy to sell to ya if it would help a blog buddy, other wise I’ll probably just hold on. Its in great shape, you can Email me if you are interested:
tilebykarl@hotmail.com
I have been looking at all of your posts about pcps because Im looking for a hunting rifle that will eather not break the bank or last for a very long time. Do you have any ideas? eather a Benjamin Sheridan or something more expensive that will be better for longer.
Check oct 17th Kdrake, it’s a good bet the awnswer from that will suit your needs.
Thanks My 392 will be ordered soon
Kdrake, don’t try to save a few bucks on the remanufactured ones available at some places. I got one in the mail this past week and it won’t seal and hold pressure. I tried some of BB’s sugestions but its just no good. I’ll probbaly spend more in shipping to get it back and forth than if I’d just gotten it from Pyramid new…It came from airgun express and they wern’t very forthcoming with a solution when I first told em it wasn’t holding air…now I’m dukeing it out with them over the added costs and such. stick with pyramid for sure.
Picatinny Arsenal is in N.J. NOT N.Y.
There is a distributor of weilding supply and compressed gases, Praxair, loacted where I live. Instead of getting a scuba tank I am going to get one of those gaint gas cylinder of carbon dioxide and use it to fill up my airgun or buy I should buy a gaint cylinder of oxygen. What would work best oxygen or carbon dioxide? Check out the size of the tank:
http://www.magmafusion.com/mag2000gw.gif
With one of those tanks I would have enough gas for years and years.
Oxygen WILL KILL YOU! It will cause your gun to explode.
Look at these photos:
/blog/2007/5/please-be-safe/
B.B.
Hi you need some imput as to useing a scuba tank for gun fills. I am a certified master diver as well as a air gunner. that said 1 not all dive shops will fill a tank for you if you are not a certified diver it is not about what you will do with the air but their libility dive shops are not under law as to the use of air for diving it is a self regulater enterprize to buy tanks or get them filled or tested you need to be a certified diver. 2 tanks have to be visual tested every year to be able to filled and hydro tested every 5 years this is about them being safe to be filled to handle the pressure. when doing a hydro the tank is filled to 8/5 of the working pressure for example a 3000 psi tank will be filled with water and pressurized to 4800 psi it is messured before pressurizing and again after pressurizing if it does not come back to the size required it fails the test. The reason .they use water and not air a tank will crack if filled with water but will explode if filled with when testing if filled with air. Air is compressable and water is not.one orther thing all tanks have a date stamped in the matal when they were made it’s a mo and year also it will be stamped every time it has been hydroed. ( note luxfur tanks have had a recall on tanks made befoe 1989 their was an alloy problem and any tank with a date of 1988 or older is not safe and can not be hydroed of filled so if you buy a used tank and don’t know this you just got scrap aluminum , their is a lot more to this than just getting a tank for filling your gun and forget compressers the price of a compresser that will go to 3000 psi is out of sight that is why divers never but compressers. i hope this is a help howie ps divers breath air not o2 so tanks are filled with air
I wonder if someone will make a;
1. A kit to make the manufactureres pump run off the car battery.
2. A PCP air rifle with a smaller cylinder, and a built-in pump to recharge it between shots. Imagine a Sheriden .20cal or Sharp Innova that has enough charge to fire 5 – 10 shots and between shots it can be recharged?
3. A Pneumatic – Co2 air rifle, fire a shot, lift the pump handle, that activates a charge of Co2 into the chamber, which can be compressed further by compressing it with the pump?
4. Cylindrical aerodynamic .177 pellets? That would change things, the high velocity of .177 and far less loss of BC. IMO that would be the best thing for air rifles.
My 5th suggestion was going to be;
Air rifle that uses a soda stream bottle? Dont know how much pressure they have yet.
Ken,
On item 1, why couldn't you just use a commonly available inverter that plugs into the 12V socket and provides a 110@60Hz receptacle? I have one that the kids use to watch movies on my laptop during long car rides, and it works like a charm.
I'm not sure that Item 2 is much more practical than a regular pcp and a hand-pump that are available today. Less weight on the gun and better leverage on the pump.
Item 3 sounds interesting. I'm not sure why it hasn't been done, but maybe it's just my ignorance showing.
Conical pellets are available, and B.B. has addressed them a number of times already. The main points he makes are that they are much harder to start in the barrel being solid and that they aren't as stable in a barrel rifled for diabolo pellets. The twist rates aren't right to get them to the point of being spin-stabilized during flight and you lose the drag-stabilization when you do away with the hollow skirt.
BTW, you might post these questions on the most recent blog as very few people monitor the older postings.
Ken
The way CO2 guns work is that the CO2 is held in vessels at pressures so high that the CO2 is in liquid phase. When the trigger is pulled, the valve allows a small amount of the liquid to escape, and it expands violently into a gas which propels the pellet. Compressing liquid CO2 is physically impossible. Compressing gas CO2 is pointless because the energy potential comes from the liquid changing phase, not anything the shooter does. You will not gain velocity or shot count in this manner.
Don't let me hamper your imagination though. Keep those ideas coming.
Bobby is right. Questions, especially ones like yours that spur dialogue, really belong on the current day's blog.
Go here: /blog//
Ken,
An electric PCP pump is under development. Maybe next year.
Multi-pumps with more than one shot have been around for 70 years. None are made today.
It is impossible to compress gaseous CO2. It simple turns to liquid.
Cylndrical .177 pellets are on the market right now. They are grossly inaccurate because the airguns don't have enough twist to stabilize them.
By soda stream bottle do you mean a seltzer bottle? If so, there are many CO2 guns that use the 8.5-gram seltzer cartridges.
B.B.
With regards to those inverters, ya gotta keep in mind that they suck a LOT more current on the battery side than they provide on the 110VAC side… on the order of 10x or so. If the current draw of a 110VAC pump is, say, 5 amps, it's gonna be trying to draw something on the order of 50 from the battery. With high-draw devices like this, we really gotta make sure the ratings match up.