Compressed-air tank capacity

by B.B. Pelletier

Today is Friday, when I usually have some fun, but I already did that with the dime article on Tuesday. I’m going to remain serious and address a topic that causes a lot of confusion. I’m going to talk about compressed-air tank capacity and how it relates to airguns.

As this report unfolds, I think you’ll see why this subject is so confusing. Every time I instruct a new precharged pneumatic (PCP) airgun owner about compressed-air tanks, their eyes glaze over when we come to this part.

“How can this scuba tank hold 80 cubic-feet of air? It isn’t that big!” That’s not what 80-cubic feet means.

“Well, why don’t they just say what they mean?” Because scuba tanks were developed for divers, who want to know how many cubic feet of air they have available to breathe. They can then calculate how much diving time they have, with a safety reserve built in.

Analogies don’t always work
We often use analogies to explain things like the capacity of a scuba tank. One analogy is the gas tank in a car. We might say that just because a car has a larger gas tank doesn’t mean that the car will go any faster. And the same is true for an airgun. The size of the air reservoir doesn’t relate to the velocity the gun can develop. But after that, the gasoline/compressed air tank analogy breaks down. Because gasoline isn’t compressible and air is. By varying the pressure inside the air reservoir of a PCP, we can stuff more air in and get more shots out or get more power from the same number of shots — or some combination of those two. You can’t do that with the gas tank on a car. Try to put in more gas than the tank can hold and it just overflows and spills out on the ground.

What do compressed-air tank sizes really mean?
One common size of scuba tank used by airgunners in the 80 cubic-foot tank. What does the term 80 cubic-foot tank mean? It means that 80 cubic-feet of air at sea-level air pressure are contained in the tank. Air pressure at sea level is approximately 14.7 psi. Now, follow this.

If you compress 80 cubic-feet of air to 3,000 psi, that’s compressing it 204.08 TIMES. The standard air pressure at sea level (which is accepted as 29.92 inches of mercury and can also be stated as 1013.25 millibar) is not accepted as exactly the same around the world, but it is close enough everywhere for this explanation. Notice the term millibar? That’s one-thousandth of a bar, which is a standard measure of air pressure.

A cubic foot of air at sea level on a normal day (and a normal day has a specific definition) measures just over one bar of pressure. Here’s the interesting part. If you multiply 14.7 times 200 bar you get 2,940 (psi). But remember that 14.7 psi is just OVER one bar? Multiply 14.5 times 200 and see what you get. The answer is exactly 2,900 (psi). So — 200 bar equals 2,900 psi. And 206 bar is very close to 3,000 psi.

What does that tell you about the 80 cubic-foot scuba tank? It tells you that if it’s pressurized to 3,000 psi, it’s holding just over 200 bar (actually 206 bar) and you now know that number (206) does relate to how much air the tank is capable of holding if the actual internal volume is around ONE cubic foot!

There are plenty of compressed-air tanks that hold air at 206 bar but are not called 80 cubic-foot tanks. I own a couple of small scuba tanks that hold 6 cubic-feet, each. Guess what? They’re pressurized to 206 bar (3,000 psi.), but the internal volume is much smaller than that of the 80 cubic-foot scuba tank. They hold much less air, but it’s at the same pressure. What does that mean? It means they’ll start dropping in pressure from 3,000 psi much sooner than an 80-cubic-foot tank will — given that they’re both filling the same airgun.

Stay with me
I’ll make sense of all of this in a moment, but first I need to tell you about one more thing — the carbon fiber tank. Actually, this tank is just wrapped with carbon fiber for strength. It has an aluminum “bladder” inside that holds the air, and the carbon fiber wrapping just adds tremendous strength to the bladder.

A common size of carbon fiber tank is the 88 cubic-foot carbon fiber tank. Okay, so it’s 8 cubic-feet “larger” than an 8 cubic-foot aluminum scuba tank. It must hold a little more air, but not that much. Right?

Yes and no.

An 88 cubic-foot carbon fiber tank does hold just 8 cubic-feet more air than an aluminum 80 cubic-foot scuba tank; so for breathing purposes, it holds onlyΒ a little more air. That’s because people who breathe that air do so right down to almost the last cubic-foot — at least from an airgunner’s perspective. They use regulators that drop the air pressure that they breathe down to an acceptable level, and that level changes with the depth they dive.

But an airgunner usually needs air that’s pressurized to at least 2,200 psi just to start filling a PCP (that’s really the pressure at which many of the PCPs finish), and 3,000 psi is a very common maximum fill pressure these days. A tank that’s pressurized to 3,000 psi will usually give only one to three complete fills of a gun before the tank’s pressure starts dropping. It will still provide many more fills, but each of them will finish at a declining pressure. This is where an 88 cubic-foot carbon fiber tank shines, because more of the air it holds is at higher pressure, so it will give MANY more full fills to a PCP than the 80 cubic-foot scuba tank! How many more depends on which gun you’re talking about, but there will be at least 20-40 times as many full fills in the 88 cubic-foot carbon fiber tank.

WHAT? How can something that is only a little bigger hold that much more air?

Actually, an 88 cubic-foot carbon fiber air tank is SMALLER internally than an 80 cubic-foot scuba tank! Remember — we’re not really talking about the volume when we quote the size of the tank. We’re talking about how many cubic feet of air AT SEA LEVEL PRESSURE the tank will hold. The difference is like the difference between a year and a light year — and it’s not just a third less calories!

The smaller 88 cubic-foot carbon fiber tank is squeezing its air like a miser squeezes a toothpaste tube — trying to get the last bit of use out of what’s inside. As a result, you get one complete fill after another from this smaller, lighter carbon fiber tank. It holds air at 300 bar, which we can now calculate to be 4,350 psi, but filling stations commonly fill these tanks to 4,500 psi (310 bar). And it takes a long time and many gun fills for the pressure inside to fall below 3,000 psi, where the tank can no longer give complete fills. At that point, it acts just like a scuba tank — and the top of each fill declines from the fill before.

Do you see why low-pressure PCPs are so great?
This is one of the reasons I pushed so hard for the Benjamin Discovery to use a 2,000 psi fill. I actually wanted 1,800 psi as the max. Can you imagine how many more fills a gun like that gets from any compressed-air tank?

What’s in a name?
This report was prompted by confusion over the latest carbon fiber tank from Crosman. They call it a 342 cubic-inch carbon fiber tank, which has no meaning in light of the explanation you have just read. It accepts a 4,500 psi fill like most carbon fiber tanks, but I think Crosman is stating the actual internal volume of the tank rather than it’s air capacity. I showed you a picture of me holding this tank at this year’s SHOT Show, and you can see that it isn’t as tiny as it appears in the Pyramyd Air description. I believe this tank probably holds 40 to 50 cubic-feet of air, according to the explanation given here, but we’ll just have to wait and see.

Conclusion
What you want for your PCP, Grasshopper, is a tank that holds many cubic-feet of air at very high pressure. Carbon fiber tanks fill the bill. Such carbon fiber tanks weigh only half of what the lesser scuba tanks weigh, but of course they do cost a lot more.

Crosman’s new carbon fiber tank is a larger one that should be good for PCPs because it will also be lightweight.

93 thoughts on “Compressed-air tank capacity”

1. Desertdweller

That is a good explanation, but it is still hard for me to get my mind around the concept that a 88 cu. ft. tank can have less internal volume than an 80 cu. ft. tank.

I have no experience with shooting PCP guns. But when I was racing my car, I’d bring a steel air tank charged to about 120 psi. I thought it was neat that the filled tank was noticeably heavier than when the tank held air at ambient air pressure. You could actually feel the extra weight when lifting it!

Les

• twotalon

Another way of looking at it…
Niether tank has that much internal volume. It’s how much air that can be stuffed into them when the air is starting at standard atmospheric pressure.
If you tried to fill both to the same pressure, the larger physical size tank would have more air in it.
If they were the same physical size, but one was filled to a higher pressure than the other, then that one would have more air in it.
If you filled the smaller one to a higher pressure than the bigger one by the right p.s.i. they could hold the same amount of air.
If you fill the smaller one to an even higher pressure, the smaller one can hold more air than the larger one.

So when we talk about these kinds of tanks, we are not talking about physical size like your water heater or your shop compressor tank or your gas tank. We are talking about how much air can be stuffed into them at some pressure without blowing up.
Note that B.B. said that the higher capacity tank with smaller internal volume can hold more air? It’s because it can be filled to a higher pressure.

twotalon

• Mr B.

twotalon,

Thanks. Your explanation makes sense to me. The following is probably a dumb question.

However, how do I relate it to the Benjamin Discovery and its Dual Fuel capability? It gets about 25 full power shots on HPA at 2000 psi, but many more shots running on CO2 at a pressure of around 850 psi which I think is the operating pressure of that gas. Doesn’t make any sense to me. Help!

Bruce

• twotalon

Bruce…for shame..B.B. has explained this before….

When you use CO2 you are filling with liquid, not just gas. If you filled with gas only, you would not get crap for a shot count. As long as the liquid holds out, the pressure holds up as the liqiud keeps boiling off to produce more gas.

A note ..
My shop compressor has a 20 gal tank. That’s 2.67 cubic feet, but it sure is a lot bigger than a scuba tank.
80 cubic feet of air at standard atmosheric pressure is nearly 600 gallons. There is that much air squished into an 80 cubic foot tank when it’s full no matter what the physical size or the pressure required to get it in there..

twotalon

• Mr B.

twotalon.,

Oops, thanks. Don’t rat me out to B.B.

Bruce

• Chuck

Does this help? You can get 88 cubic feet of air into a tank of any size if you compress it to a higher psi. The question is is the tank strong enough to hold the increased pressure. The carbon fiber tank, which is smaller in physical size, is stronger than the scuba tank, and can hold more cubic feet of air than the scuba tank because the air can be compressed to a higher psi because of its extra strength. A scuba tank will not safely hold 4,500psi. If it could, it would hold more air than the Crosman carbon fiber tank.
-Chuck

• Chuck

Desertdweller,
The air in an 80cf aluminum tank filled to 3000psi weighs 6 pounds. And FYI, an 80 cf aluminum tank holds only 77 cf of air. They cheat and round up to 80. Not a clue why.
-Chuck

2. J-F

That is a very interesting and comes at a very good time for me but I joke woke up and I think I need some caffeine to help me fully understand all of this.

If I understand that right it seems it would be better (to me) to get a smaller tank (90cu/in like the smaller carbon fiber tank Crosman just came out with) with a higher fill pressure. That way you get less fills BUT you get full fills, no?
Fills aren’t expensive between 5\$ and 10\$ per fill but the smaller bottle is also a LOT cheaper so Iguess it’s just a question of price. For me anyways as I have a filling station less than 15min away.

But then the shoebox becomes a more tempting option. Guys talk about refilling a 3000psi 68cu/in in an hour and a half… From empty! So no need to go by it every few hours to lube it.

Another great money spending blog π

J-F

3. caveman

342 cu in at 4500 psi would be about 60 cu ft at at sea-level air pressure. So the carbon fiber tank from Crosman would be about 60 cu ft. Herb, Jane, or someone help me I think this is over my pay grade!

4. David Enoch

I recommend to people who plan to get into PCPs that their first purchase should be a 4500 psi carbon fiber tank. Now, I recommend a Shoebox Compressor and a small Carbon Fiber tank instead of just a larger Carbon Fiber tank. Anyway, once the tank or tank and compressor are paid for, it’s time to pick your airgun. It’s so common for people to buy the airgun first. They can’t shoot it so they buy a pump. The pumping gets old so they buy a 3000 psi scuba tank. They only get a few fills and eventually get a carbon fiber tank.

David Enoch

5. se mn airgunner

BB,

I’m a wannabe PCP owner. Don’t really know much about them other than they are way more accurate than a springer. I am concerned by your comments about the number of fills a tank can take. I figured these things were permanent? Is the internal reservoir of a PCP also limited to a number of fills? In other words, are PCPs like a metal springer where the spring eventually wears out? I thought/hoped PCPs lasted basically forever if well maintained whereas a springer will eventually wear out no matter how well you treat it.

Confusedly yours,
se mn

• B.B. Pelletier

se mn airgunner,

You have misunderstood me. Compressed-air tanks last a very long time. I have a scuba tank that was made in the 1980s and is still operational.

I wasn’t talking about tank life in this report. I was talking about filling the tank as full as it will go, and then commenting on how many fills the tank will give when connected to airguns it fills.

Compressed-air tanks do have a limited life, but it isn’t a short time. Carbon-fiber tanks are limited to 15 years of service after their first fill. They are also subject to inspections on a periodic basis. Scuba tanks last until they fail an inspection.

PCP airguns mostly have an indefinite life, but the makers of 10-meter guns with removable tanks say their tanks are no good after 20 years of service.

B.B.

• se mn airgunner

OOOooooooo,

You’re talking about how many fills a full capacity tank can provide a pcp reservoir!!!!

I feel like I’m in 3rd grade and I just understood how simple division works.

• B.B. Pelletier

se mn airgunner,

Don’t feel bad. Each of us who now shoots a PCP went through exactly the same learning process. This isn’t anything that is intuitive, but it’s also very understandable, once it’s explained.

After you learn this, you take the viewpoint that a PCP is a lot like a .22 rimfire. Easy to operate and shoot and no special techniques required.

It’s very light over here on the Dark Side! π

B.B.

• Wulfraed

It may need to be mentioned that the AirForce tanks ARE stamped for inspection dates, and DO need to undergo a pressure test every five years.

6. DerekB

Do pressure vessels cause a quiet, but insistent, internal unrest in anyone else? Any time an air compressor kicks on (and that’s only filling a vessel to 120psi!) some animal part of my brain starts to wonder ‘what if it explodes!’

Watching someone fill a scuba tank would probably cause me somewhat more quiet distress.

• B.B. Pelletier

DerekB,

I felt the same way the first couple dozen times I filled an compressed-air tank. Now it is second nature and I don’t think about it.

But I still respect the technology and handle it safely.

B.B.

• caveman

No more than the controlled explosions in my car or lawn mower. The thing that makes me nervous is when someone is filling a 200 bar vessel from a 300 bar vessel with just a valve (without a regulator) or filling very fast.

• Chuck

DerekB,
Filling scuba tanks can be dangerous if they are not maintained properly. A dive shop will not fill a tank if it hasn’t been hydrostatically tested in 5 years (Federal reg) or visually inspected in one year. A steel scuba tank should last for about 40 years, an aluminum one about 15. Some shops will refuse to fill an aluminum one after 15 years.

A major cause of failure is rust, another is fatigue caused by the expanding and collapsing of the tank through the fill and empty cycle. Like bending a metal plate back and forth untill it breaks. A cause of rust is not ensuring dry air when filling or leaving the valve open on a completely empty tank. This concerns me if a scuba tank is filled by an airgunner using a home air compressor. The moisture will not get filtered and internal rust will develop undetected, and tank inspections will not get done.

I have wondered about the tanks on our guns, too. Surely they face the same demons as scuba tanks do. I have never heard of a gun exploding but I wonder what happens when one does.

-Chuck

• derekb

On my show last spring, I saw a lot of CO2 tanks. I ran into some stamped from as long ago as the 30s, which really speaks to the survivability of lower pressure vessels. And made me wonder what those tanks had seen, before my fog machine.

7. Fred DPRoNJ

The equation, if I remember correctly, for calculating volume or pressure is the Thermodynamic (Boyles’ law?) formula of PV=nrT. Since nr and T between the SCUBA tank or carbon fiber tank and the gun reservoir should be the same, the formula can be PtVt=xPgVg where Pt and Vt = are the pressure times volume in the tank = unknown times pressure in gun times volume of gun reservoir. You know the beginning pressures, the volumes (however in this case it’s actually the internal volume of the tank or gun reservoir, so solve for x which will tell you how many times you can fill your gun.

OK, now we need Pete Z or Herb or Jane (Chuck perhaps you want to weigh in or Wilfraued – others who happened to like thermodynamics in college) to correct me.

Time to go to work for the boss and earn some money.

Fred DPRoNJ

• Chuck

Fred,
I’m no expert on thermodynamics. I’m not even at a rookie level. I believe your formula, and bow to the other names on this list.
-Chuck

8. David Enoch

There are several tank calculators available on the web that you can use to get an approximate number of fills you can expect for a specific gun from a specific tank. The Yellow Forum has a link to one. One thing to remember with PCPs is that we are not using up the air in the tank as much as we are using up the pressure. If you need to fill your gun to 3000 psi and your tank pressure is down to 2900 psi you will not get a complete 3000 psi fill. So even though the tank still has a whole lot of air left, it is empty as far as the pressure required to fill your gun. It is time to refill your tank.

David Enoch

• J-F

One of the best I’ve encountered is the one made by our own Lloyd Sikes the creator of the Rogue.
http://calc.sikes.us/2/
He also has a nice PCP air efficiency calculator
http://calc.sikes.us/1/
They’re very nice and easy to use.

J-F

• Frank B

If I may,J-F….I’d like to add a “cherry on top” ANYONE who shoots or is remotely interested in big bore airguns,our own Lloyd has some really awesome must see videos on Youtube!
You can see them all on his channel,found on Youtube by entering “1227air500” in the search box.You WILL be glad you saw them! He does fascinating things in his garage laboratory.

9. Colt

Hey Tom. Can you make a cool, target that anyone can make then write a blog about it?
Like with tools and materials that everyone has in their junk drawer.

• B.B. Pelletier

Colt,

I’m not sure what you want. Are you asking for an action target? Or a target trap?

B.B.

• Colt

Yeah. Like a spinner or a field target. Just Something fun. But only of you have the time to do a report.

• B.B. Pelletier

Colt,

Let me give it some thought.

B.B.

• Colt

Thanks BB π

10. Matt61

B.B., so you have two scuba tanks. How do you manage to get them filled? Wayne said that he needs to make up stories for his dive shop because they either don’t like or are not supposed to fill tanks for other than scuba diving. Another logistical hassle with scuba tanks! I’m sure you can’t keep a dive shop fooled forever. And how expensive is it to fill your tanks this way?

I’m supposing that an air tank filled to high pressure has minimal chance of rupturing. That could be really destructive.

Otherwise, I’m all in favor of ways to fire off multiple shots quickly. My dirty secret is that for various reasons, I have been shooting at a much reduced rate–30 shots at a time every few days. The accuracy definitely was starting to suffer. Now, with my RWS Hobbys restocked, I’m back up to 120 a day, mostly with my IZH 61, and it feels terrific. It seems like I’m not really getting into it until 50 or 60 shots. And when I do my final groups with the B30 at the end, I do significantly better than when shooting fewer shots with the B30 by itself.

Matt61

• Fred DPRoNJ

Matt,

I also have two SCUBA tanks – both steel, one 80 the other 88 cu. ft. (high pressure – 3300 psi). The local dive shop has no problem filling these tanks and I make sure I tell them it’s not breathable air but airgun or paintball air. Sometimes, they’ll even overfill the tanks by a couple hundred psi because of that. They have no problem doing this because they know I bring the tanks to them for the Visual Inspection Program and hydrostatic testing (the latter every 5 years, the former once per year). I’ve been told that the steel tanks last forever especially since we don’t take them down much below 2,000 psi and therefore the steel is not worked as hard as a tank that’s drained to a couple of hundred psi.

Fred DPRoNJ

• B.B. Pelletier

Matt,

Same answer as Fred. The dive shop resistance mostly ended in the 1990s. Of course there will always be exceptions.

B.B.

• pete zimmerman

My tanks are marked with yellow/black tape (rather like crime scene tape) “Paintball Air; not for breathing” or something very like it. Along with a notice not to fill the tank for SCUBA use.

Seems to work at the shops around here.

• Matt61

Hm, my thinking was along the lines of the T’pau of Vulcan who says, “The air is the air. What is to be done?” Didn’t know there was a distinction between consumable air and other kinds.

Matt61

11. jimorus

Speaking of βairβ maybe a little thought on the different uses of the word may also be in order.
In a healthcare setting air refers to the stuff we breathe. It is pretty simple. In the same setting oxygen refers to one of the elements contained within the air that we breath. The two are totally different and should not be confused and in the medical world they are not confused or confusing. The hospital has oxygen coming from a bulk tank and piped throughout the buildings and uses it in cylinders for mobile operation.

Hospitals do not usually refill their own small tanks from the bulk tank.

But the construction world things get confusing really quickly. βAirβ is used during gas cutting and welding and is in reality oxygen. Then we also have βbreathing airβ which is the same stuff we breathe filtered and compressed into a tank which can be a small carbon tank for an emergency breathing system or the same style cylinder as the oxygen used in welding but the threads on the regulator can be different. After that is βcompressed airβ which is the stuff you have in your tires and use to blow up your football. In an emergency it will support life but no one really cares if it has a few contaminants in it. I mean itβs inside your tires for goodness sakes.

Filling a tank at a scuba shop gets you βbreathing airβ as opposed to compressed air, although some divers refer to it as compressed air. Ideally it is filtered and clear from contaminants so from my background it is βbreathing air.β

Knowing your audience is imperative when discussing the product you need.

A new PCP person, especially someone less experienced could have had some lessons from dad on cutting or welding and see that big 6000 psi tank in the garage or barn or workshop, that dad expressly called air, and fudge together enough pieces parts to adapt it to filling his gun and that could be a disaster. High pressure oxygen reacts violently with petroleum products and some other oils.

My wife comes from a medical background and laughs at my uses of what are improper terms in her world.

Sorry if this was too far out there
jim

• Wulfraed

Filling a tank at a scuba shop gets you βbreathing airβ as opposed to compressed air, although some divers refer to it as compressed air. Ideally it is filtered and clear from contaminants so from my background it is βbreathing air.β

I have vague memories of an old show (was it Sea Hunt, or just an early episode of CSI on a lake — yeesh, a near 50-year span to search) in which the case came down to someone using a gas-powered compressor to supply breathing air — where the compressor intake was sucking up the exhaust from the engine… Not very healthy for the divers — to put it mildly…

• jimorus

There are cases of gas powered compressors with the exhaust leaking adding carbon monoxide to the tanks in excessive proportions. It is spoken about on the diving boards Divers have had cases of CO poisoning from bad air.

These cases can more readily occur in areas where electricity isn’t always availble and the resort or dive operation fillsjim their storage tanks via a gas powered compressor and then fill the diver’s tanks from the storage tanks.

• Fred DPRoNJ

I remember that episode – Sea Hunt with Lloyd Bridges!

What is good about the “breathable air” is that it is filtered and dry. No worries about rust from water vapor forming in the compression chamber or mechanisms.

Fred DPRoNJ

• Chuck

Wulfraed,
Those are called Hookas. They are in use today. I don’t know the maximum depth for them but I’d guess 40 ft or less.
-Chuck

• Chuck

I just saw on the web some Hookahs (spelled it right this time) can support two to four divers up to 85 feet. They can be gas or electric powered.
-Chuck

12. Mike

My Sheridan compreses air just great every time I pump it up! π

Mike

13. Spritzer

DerekB,

I think about it every time. I worked at ODOT for a few years and a mechanic friend shared the stories about what can happen when a split rim fails. I believe they were true, but I don’t think he witnessed them. I’d say that the lesson is to always know what you are doing and to practice safety at all times. Probably a good model to keep in mind for most aspects of life.

14. kenholmz

B.B., thank you for another informative blog. It helps to get some cognitive perspective on the subject.

Recently you wrote about the new 1911 Winchester Model 11 CO2 pistol and the new P38 Walther. I had to think for a while about even the basic concepts regarding single and double action with respect semi-automatic pistols. I have long understood the difference in revolvers. When I shot myself in the foot I had to cock the revolver (makes all the more embarrassing). But I had never even considered this for the “autos”.

As best I can make out, the P38 is double actions initially in that you pull the trigger and it both cocks the pistol and then uses blowback to cock the pistol again.

With the 1911 you manually cock the pistol for the first shot and again blowback cocks the pistol.

And so, whether you manually cock the pistol or it is done by blowback, the pistol single action. I had to think about the same pistols without blowback. I believe I understand now what you were saying about the two pistols. At least I hope I do.

Ken

• B.B. Pelletier

Ken,

You got it right. If the hammer has to be manually cocked, either by the shooter or by an action of the gun, the gun is single action. If just pulling the trigger will cock the hammer and also fire the gu, it’s double action.

Single action has the advantage of having a better trigger pull. Double action has the advantage of being safer for people unfamiliar with firearms, because it’s harder to discharge accidentally.

B.B.

I have a Benjamin Discovery and the hand pump that came with it. The air rifle is really good and the accuracy is amazing. I have had trouble with the hand pump that came with it though. I have tried to follow all the instructions but it has stopped working twice. It seems to be the small o-ring at the bottom of the center piston. It gets hot fast and fries.

Question on pumps. Is hydraulic oil acceptable for lubrication?

I am looking at a 40 cu in aluminum bottle with valve that is rated for 3000psi. From what I have read, this should work fine for my needs.

Is there an easy way to locate places to get the air tank filled. They seem to be rather elusive.

Thanks for the great information site,
Tom

• B.B. Pelletier

Tom,

If you know about the small o-ring you have disassembled your pump. No! Hydraulic oil is not acceptable in this pump! The temperature in the pump rises too high for conventional lubricants to tolerate and moly grease coated lightly is the best lubrication. When I repaired pumps I used Beeman M-2-M.

Yes, you can get by with a lower-rated scuba tank because of the lower max fill pressure of the Discovery. That’s one of its many advantages.

B.B.

Thank you for the fast reply. A correction to my earlier post. I referred to a 40 cu in tank. It is a 40 cu ft tank.

Yes, I have had the pump apart. I contacted the pump manufacturer (Sun Optics) and they sent an entire set of o-rings and instructions. Thanks for the advice about moly and Beeman M 2 M. I think I have both already.

• Fred DPRoNJ

Tom,

one other thing that you may or may not be doing. The high pressure pumps should not be pumped continously more than 5 minutes. The reason being is to let them cool down. This may be why your o-ring has self-destructed twice.

Fred DPRoNJ

• Chuck

Lots of places. Too bad they didn’t standardize on format to make it easier to find a location.
-Chuck

• B.B. Pelletier

Jan,

Good resource! Thanks,

B.B.

16. J-F

A guy on the Canadian Airgun Forum fixed his pump to the floor of his shop/garage and made a looooong lever fixed to the wall and to the pump handle with a pivot. You all know what they say about levers right? He can pump to 3000psi with a hand litteraly tied behind his back. He says it’s super easy, it’s ugly (I’ve seen the pics) but easy and it works.

J-F

17. TunnelEngineer

B.B. and PCP air gunners
After the great experience with the CZ S200 (now available at PA as an Air Arms), I want to get a larger Air Arms rifle for target shooting, field target, silhouette. I am not getting a \$1,500 rifle. I am looking at the S400, S410, S500, S510.

Can someone please explain why is the S410 almost twice the price than S400? I know it is a repeater, but that cannot be the only difference. I have read conflicting information in PA webpage about whether the S400 has or does not have a power wheel. If all four have a power wheel, then I do not udnerstand what is the difference between all these different models, and I am looking at all of them on the comparison table.

Help is appreciated

T.E.

• B.B. Pelletier

TE,

The S400 clearly has a power adjuster on it that can be seen in the photos.

Edith will add that to the description.

Why is it so cheap? Last year’s model.

B.B.

• TunnelEngineer

Thank you B.B.

18. Primo

BB super explanation. Now the thing is I can’t find a scuba shop where I live that will fill or has the capacity to fill up to 4500 psi. I did find new scuba tanks that are 100 cubic foot capacity ,but only up to 3000 psi. Could you please give me an idea of how many fills I could get for my 500 cc Sumatra at 2900 psi, and for my Marauder 215 cc at the same psi? Using the 100 cubic foot tank. Thank you PR

• B.B. Pelletier

Primo,

You’ll get about 7-10 fills to 2900 for the Sumatra (at least) and maybe double that for the Marauder.

B.B.

• Chuck

Primo,
You can calculate this for yourself with this handy dandy site.

http://calc.sikes.us/2/index.php

For your Marauder, which you would normally fill to 2500psi, plug in these values in this order:

Cubic foot (CF) rating of your air tank (from chart below) – 100

PSI pressure rating of your tank – 3442

Actual PSI in your tank – 3000

CC of your gun’s tank – 215

Fill the gun to this PSI – 2500

Fill the gun when it gets down to this PSI – 1800

The answer I get is – 39.4

-Chuck

• Primo

Chuck thank you very much went to the site it’s excellent and very easy to use. I’m going to have a ball with my Sumatra in its low setting. I can get that rifle to shoot crosman 14.3 at high 900 in the low setting, the power is way up there, and now with a better notion of fill capacity I’ll be shooting it more. One thing I do to extend the number of fills is to use the hand pump for the last couple of hundred psi, usually I don’t have to pump more than 25 to 30 times counting up & down strokes till I get to 2900. It also serves as a upper body workout. Thanks. PR

• Chuck

Primo,
Glad you found it useful, but all credit goes to J-F who sent the original link a couple days ago. That’s a good idea there of topping off with a pump. That’ll make the source tank last a whole lot longer. The dive shops don’t care how much air is left in the tank before they re-fill it. They still charge the same. Might as well milk as much air out of it as possible.
-Chuck

• Wulfraed

For your Marauder, which you would normally fill to 2500psi, plug in these values in this order:

My .177 Marauder is the only PCP for which I’ve run a “burn down” test (since I could read the pressure gauge after every 10 shots through the chronograph)… In factory settings, I find the plateau to be from 2700 to 2200 PSI… Filling to only 2500PSI means I’m halfway through the efficiency point. Granted, that was when my apartment was at 220ft altitude (SanFran Bay area) — not the 850ft of Grand Rapids.

19. Matt61

On the subject of breathable air, I understand that the closed circuit (Draeger) breathing apparatus used by the Seals had some developmental issues. One was a certain type of malfunction that blistered and fried the lungs of the user….

In other news, I was looking through a catalog for Champion’s Choice, the place I bought my Anschutz from, and a lot of it looked like it was from PA. Looks like airgunning is getting a bit of respectability.

Matt61

• Chuck

Matt,
Those are known as re-breathers. They are fantastic machines in that they allow you to get much closer to the wildlife because there are no loud disturbing bubbles emitted and they allow you to stay down much longer, but they do have reliability issues. They mix chemicals that if they don’t get mixed properly create toxic air. There have been several deaths. I have been diving with users of re-breathers and suffered acute envy. π They are a bear to travel with though. They don’t exactly fit in your dive bag.
-Chuck

• duskwight

Chuck

A friend of mine is a fan of underwater hunting. He uses a silenced regulator and sort of silencer for his scuba exhale – a device that “cuts” exhaled mix into very small bubbles, creating a “mist” that generates very little noise and he says the below 5 m those tiny bubbles seem to dissolute in water without even reaching the surface.

duskwight

• Chuck

Very interesting! I have not heard of that before. That deserves looking into. I wonder if that is available in the US?
-Chuck

• Matt61

What is your friend hunting underwater, and how has he armed himself? π

Matt61

• duskwight

Matt

Pike, zander, bream, large perch, catfish and so on. I’m not much in spearguns, but he has some gas-spring powered gun and a sort of a crossbow with 4 elastic round wires driving a spear.

duskwight

20. duskwight

B.B.

It’s boasting time! π
On Friday I finally received a lot of of small details, namely safety assembly, several pins, lugs and other stuff for bypass control system. A heavy handful, most of them are nothing special, but I cannot go on without them. A little work on fitting and cleaning surfaces with reamers, scraper and needle files and a little polishing. Hard job, literally – some of them are above 60 HRC, that’s where diamond files work their best.
Larger parts are still pending: QC found 1 dimensions mistake, and bad blueing on 1 piece, so they returned it back to machinists and chem labs. There’s still one good thing in that – this way I’ll receive all the lower engine parts in one big heap. Guys report workers sometimes mutter against me – “the guy wants to build a spaceship, no less!” Well, I never promised anyone an easy life and I don’t ask anything above precision and beyond their skills. That heap will contain 4 difficult parts with lots of precision drilling and milling.

duskwight

• B.B. Pelletier

duskwight,

Okay, happy boy! Don’t forget to take pictures of the parts before you file them! We want to see this in great detail! π

Any estimate on when the final parts will be delivered?

B.B.

• duskwight

B.B.

Well, if you want to give God a good laugh – make plans and voice them, but I plan to have them by the first week of May. Then comes a receiver – as far as I know, by last Wednesday they were still debugging CNC code for my piece, but once it’s written and tested – I guess it’ll take no more than 6 hours, then some chem treatment. By that time I’ll have my barrell cut, sized, turned, threaded and crowned and I hope all the small springs for trigger and cocking/interceptor assemblies found and tested and mainsprings cut down to size and tested.

duskwight

21. david

hi i was just wondering if you had a post about were to find old airguns. i realy want a rws 75 but dont know were to find one.

22. david

thanks for the help means alot to me.

23. 3ric Johanson

Nice writeup, thanks for publishing this. As a scientist and diver, I’d like to offer the following feedback on your post:

– You are sharing a bunch of information about pressure but I don’t think it’s all that helpful to provide information about bar/millibar/psi/kpa etc etc in this sort of article. It might be much more clear to just express it all in PSI, and provide some utilities for conversion to different units. It is handy that 1 bar is normal air pressure, but I think it’s just a distracting factoid in your otherwise really helpful and insightful writeup.

– If you have a 88cubic foot tank @ 4500 PSI and you fill a 5.7 cubic foot paintball tank, what’s the resulting pressure in your source tank? It is: (4500 psi * (88cf – 5.7cf)) / 88cf = ~4200 PSI. In fact, you could fill five 5.7 cubic foot tanks if you want to maintain above 3000PSI .

24. Jeff

Hi B.B.,

Just curious, how many refills do you get from a:

40 cu ft tank
60 cu ft tank
80 cu ft tank

To a cylinder like the S200? Just want to know if the pumping is worth the effort or it’s really a relief to own a dive bottle.

Thanks!

Jeff

• J-F

This is an old blog, you’d have more chances of getting your question answered by posting it in todays blog. Don’t worry about being off-topic.
You can get to the new morning blog that is published every day of the week right here:
http://www.pyramydair.com/blog/

To know how many fills you get per tank you will need to know the volume of your tank, at what pressure you’re refilling and up to what pressure.
Just enter your info in the calculator provided here: http://www.calc.sikes.us/2/

If you LIKE pumping keep the pump, if it reduces the time you’re spending shooting because it turns you off to pump it back up afterwards, I’d say get a tank.
I got myself one of those tank: http://www.pyramydair.com/s/a/Air_Venturi_Carbon_Fiber_Air_Tank_Fill_Station_4500_PSI_90_Cu_In/4708
If you have a paintball field close by they’ll refill those for cheap (they charge me 10\$) with nitrogen so it has no moisture in it. You’ll get a lot of full fills compared to a 3000psi tank that will give you a lot of partial fills because you’re starting with a pressure of 3000psi.

Hope this helps, if you have more questions or are not sure about something, don’t be affraid to ask, that’s what we’re here for.

J-F

• Jeff

Nitrogen so that no moisture… 3000 psi compressed air from dive shop is moisture free right?
one more thing is, is it more shots per fill for nitrogen?

Thanks,
Jeff

• J-F

X2 what he just said.
Most of the air we breath is nitrogen (78% to be exact) so you’re not going to get an increase in shot count but it will have no moisture at all.
Paintball shop all use nitrogen as it’s cheaper than breathable air. If you have access to a 4500psi source forget the big tanks and go straigth to the smaller one I posted in my other comment.
The bottle is WAY cheaper and comes with everything you need to fill up your gun.
If you go with the scuba type of bottle don’t forget that they’re made to be use under water where they weight a fraction of what they weight on land. These thing are heavy and of course the bigger the volume, the heavier the bottle will have to be.
The small carbon fiber tanks are feather weight.

I found pumping was cutting on my shooting enjoyement. Filling from a tank is sooooo easy. Hook up the tank, open the valve, close the valve, unhook everything and you are done. It takes more time to get the tank out than to actually fill up the gun.

J-F

• GenghisJan

Hi, Jeff. Pure opinion here; big grain of salt. IF you have a convenient source for 4500 psi compressed air, skip the hand pumping and go directly to a 4500 psi carbon fiber tank. If your compressed air source is limited to something like 3500 psi, it might be a tougher decision; Lloyd’s fill calculator that J-F linked to will help to decide it.

Forget aluminum or steel scuba tanks unless your air source is limited to ~3500 AND you will not lug your tank around. CF tanks are much more portable.

I think nitrogen is only rarely your best value. E.g., if you don’t live near a dive shop, you might do a long-term rental of one of those huge, 6000 psi nitrogen tanks. Or invest in one of those shoebox compressors. At any rate, consider nitrogen an air equivalent when using a fill calculator, modulo the possibility that a nitrogen source will start at 6000 psi!

-Jan

• Jeff,

I’m making this a homework assignment for you! You tell the rest of us how many fills.

You can do it in a guest blog. π

B.B.

• Jeff

Based on the calculator:

40 cu ft tank
pressure rating: 3000
actual rating: 3000
cc of gun: 122
fill the gun to this PSI: 2500
fill the gun when it gets down: 1400 psi

I’ll get 20 refills. I normally go out once or twice a month, sometimes I don’t… what do you think gents?
Thanks,
Jeff

• J-F

I think it depends on the price and weight of your tank.
I calculated with the small 90 cu/in carbon fiber tank that I linked above and get 22 fills.
The tank is very small and portable and retails for 300\$ with all the needed filling accessories.

So I think you have to find out where you’ll get your air from and if you can get 3000 or 4500 psi and consider the price of each tank with the filling accessories. Not all diving shops are willing to get your tank filled up and you’ll also have to consider wether you’ll be toting the tank around or not.

J-F

• GenghisJan

Yeah, Jeff. Repeat that calculation based on a 4500 psi tank, unless you’re sure you can only get 3000. I think most scuba shops will go at least to 3500 even if they don’t have 4500 boosters.

-Jan

25. Anonymous

I think they can only refill up to 3000. it’s the only one available here. The tanks available are rated at 3000 psi and I can’t find a carbon fiber tank available here. The tank in my mind is a luxfer 40 cu ft aluminum tank.

Jeff

• J-F

For 4500psi look for paintball shops or field around you, most of them have the 4500psi you’re looking for.
If you go with a carbon fiber one just order your tank from PyramydAir, I don’t think you’ll find cheaper and it has all the lines needed to plug in your rifle.

J-F

26. Jeff

Hi Guys,

I”m not sure which adapter/connector will I be needing aside from quick fill adapter that comes with the gun(with bleed valve). I read somewhere that it’s everything I need. I have the cylinder with gauge.
what confuses me are these:

MDE DIN, Gauge and hose

MDE DIN-A Clamp, Gauge and hose

These 3 seem to be an add on to the setup, but I’m not sure cause I read somewhere that I’ll only need the quick fill adapter to fit the cylinder to the dive bottle.

Jeff

• J-F

Sorry mate, I can’t help you there, I have no idea what is needed, like I told you a few days ago, I ordered the tank just like the one shown in the link I provided, it came with everything needed to plug in the PCP of my choice. All I had to do was have it filled.

J-F

• Wulfraed

DIN connectors, to my knowledge, are used on 4500psi tanks (or any tank that peaks >3000psi)

3000PSI tanks, I believe, use a simple O-ring and pressure clamp seal. The higher pressure tanks use a fitting that might screw into the tank rather than just pressed onto the face.

27. Jeff

I understand, no worries. I’m hoping someone here might know.

THanks!
Jeff