Gun-only compressors like the Air Venturi RovAir are changing the face of precharged airguns.
This report covers:
- Pressure levels
- Volume
- Automobile gas tank
- Tradeoffs
- Compromise
- Discussion
- Summary
Wow! Yesterday I said sometimes the topics for blog reports knock me down and beat me over the head. And you readers responded like my words were a command!
I thought all you were up on the technology of precharged pneumatics, or PCPs as we call them. But the questions that were asked on the first report of the RovAir portable air compressor showed me there was a lot more you wanted/needed to know.
I had planned to shoot the AirForce MicroHunter with the Lucid P8 scope today, and I will do that, but before I do, let’s review or learn about some fundamentals of compressed air, as airgunners use it. Like all reports, this one is not for everybody. But there are those who need it. If you are already well-versed in precharged operations, please help me in the comments because I think there is a host of readers who need this. And please bear in mind that there might be only 30 active readers who comment on the blog and perhaps one hundred more who sometimes say something, but for each comment there are at least 250 people who don’t comment yet want to know the same thing.
Pressure levels
To the best of my knowledge, PCP fill pressure levels run from around 1,500 psi (for a USFT rifle) to 4,500 psi for the Umarex Hammer. Many of them lie between 3,000 and 4,350 psi. Those are the pressures our compressors need to supply. There are boutique PCPs that operate on lower air pressure, but they are uncommon by definition.
Volume
The capacity of PCP reservoirs runs from the 100 cc Ataman BP-17 to the giant Hatsan 1,000 cc Hercules. Most airgun reservoirs hover between 200cc and 500cc. This is what you are trying to fill.
Imagine you are asked to blow up a balloon. They range in size, but unless it’s a weather balloon, it’s doable. Now imagine you are asked to blow up an air mattress that’s 10-inches thick, five feet wide and 6-1/2-feet long. For that you need a pump (a compressor) and an electric one if at all possible. Same thing for PCPs.
So, what’s best to get? Well, what are you trying to do?
Automobile gas tank
If an automobile gets 25 miles to the gallon and has a 20 gallon tank, the driver knows he has a maximum theoretical driving range of 500 miles on one tank of gas. The Indianpolis 500 is a race that goes 500 miles. With a 20 gallon tank that car could theoretically run the entire race and never need to stop for fuel. But it has a top speed of 83 miles per hour and the race would have been over a long time when it crossed the finish line.
An Indy racer that can go 240 mph gets around 4 miles per gallon. So that car would need to carry 125 gallons onboard to make it to the finish without refueling. One gallon of gas weighs about six pounds so 125 gallons weighs 750 lbs. That’s way too much to carry in a race and Indy cars have to use special fuel cells that hold 18.5 gallons. That’s 74 miles between fuel stops.
Tradeoffs
Obviously I’m talking about tradeoffs. Let’s consider airguns. The USFT rifle I own has a maximum useful fill pressure of 1,500 psi. With that it gets 59 shots of .177-caliber JSB Exact Heavys going out at around 885 f.p.s. with 30 f.p.s. variation. That is enough velocity to kill a squirrel reliably out to at least 50 yards (and beyond for an accomplished shot). BUT — would you ever hunt squirrels with a USFT? That would be like going grocery shopping in an Indy racer.
USFT isn’t the rifle to hunt squirrels.
On the other hand, the Benjamin Discovery only fills to 2,000 psi and makes a great squirrel gun. And, for the guy who gets to fill it, stopping where it does is a blessing. The RovAir can do it and never break a sweat. And you get at least 20 good shots before refilling. Is it a good squirrel hunting rifle? Yes, if you want to hunt for 2-3 hours; no, if you plan to stay in the woods all week without an air supply. Tradeoffs.
Benjamin Discovery.
Compromise
An AirVenturi Avenger could be a nice PCP in the middle. It’s powerful enough for squirrels, and accurate enough for field target. In .22 caliber I got 50 shots at 36+ foot pounds and the rifle sells for $350.
Now, put a RovAir compressor into the mix and you have what for some could be an ideal combination. And Yogi, at $500, the RoveAir costs less than the carbon fiber air tank that, “… all the guys at your gun club say is necessary.”
Discussion
Getting into PCPs is a matter of determining:
What’s available.
What you can afford.
How you want to operate.
You DON’T have to buy carbon fiber air tanks, even though they are handy. Today, because reliable gun-only air compressors that can be taken most places abound, it’s less expensive to go that route. People who do so are not interested in filling large carbon fiber air tanks. They have eliminated that step and go straight from the compressor to the airgun.
When you buy an airgun of course you want accuracy, reliability, a good trigger and, most often, repeatability. Add to that how the airgun will interact with your filling solution(s), be they hand pumps, gun-only compressors or the whole ball of wax — CF tank and large compressor to fill it.
Summary
This was a quick update on the compressed air situation that exists at the end of 2023. A new technology — gun-only air compressors — is changing the landscape for the PCP.
B.B.,
There are still parts of the aigun spectrum not sufficiently covered by the small portables and that is the very powerful Big Bores. A day at the range with a big bore will still be interrupted too often using this class of compressor. The CF cylinder(s) are still needed for that. I can however see the small compressor with a power source at a hunting camp or the trailhead working.
I would still opt for the two large CF because of the advantage of reliability, minimum 15 year life cycle now extendable to 30 years, and lower weight. Remember you need a source of electricity in camp.
Based on many decades of Big Bore gas hog airguns at the range and in the field.
But yes things are in flux.
shootski
shootski,
Well said. For big bore shooters who want to shoot many times a large carbon fiber tank is still the way to go. I don’t see that changing anytime soon. Maybe a partial solution is to make the little guys more capable of filling them?
BB
– I commute by bicycle a couple days a week. On the bike I carry a little hand pump, which can barely get the tires to a firm, rideable pressure (60 psi or less, 4 bar), that you have to guess as it doesn’t even have a guage, but it is lightweight and small, and will help get me home after I patch a puncture.
– When travelling by car I’ve packed a floor pump, the kind with a pressure guage that you put a foot or two on while hand pumping, and that pump has gotten me home after plugging a punctured tire. I’ve pumped an SUV tire up from flat with the floor pump and it was a life-affirming experience. I can’t imagine doing that with the little hand pump, although I know it could theoretically be done.
– My mom had a cigarette lighter tire pump in the trunk of her Corolla, and used it on occasion because there was no way in heck she was going to use a floor pump when the car battery could do the work. Someday I too will get a cigarette lighter pump for my car.
– The gas station has a shop pump and tank and will let you use it for a quarter. It will fill all 4 tires in a minute.
– Isn’t it kinda the same with PCPs?
Cheers,
Mike
Mike,
Very good analogies. Actually on the subject of bicycle analogies, one could think of springers to PCPs as push bikes to electric scooters (not electric bikes, as those can still be peddled when the battery is empty).
I have a monstrous AV compressor and a 100 Cu.Ft. CF tank. I also have an Hill hand pump which does not see much use now. Why? I went from shooting my Edge to shooting a .357 HM1000X. Shootski has indeed touched on a good reason to have a large HPA tank or two. When you start shooting big bore, you use a LOT of air.
If I was just starting into PCPs, I would likely start with the Discovery or Maximus, assuming you can even find one these days. They are easy to fill, even with an hand pump. These days, unless you are young, one of these small compressors would be awesome.
RR, sounds like the upcoming 3622 is going to be the replacement for the Discovery and Maximus. Was told last month they’re in final testing and setting up tooling. Trying for $130 MSRP.
Do the small gun-only compressors have any provisions for removing the moisture from the air they compress? I used to install pneumatic HVAC control systems in buildings and they always had refrigerated dryers inline downstream of the compressors for that purpose. And I think that compressors for SCUBA gear would also have some sort of dryer system. It appears to me that hand pumps for PCP guns have some sort of filter that needs to be replaced regularly and might help remove moisture. Is that the case with the small portable compressors?
Elmer,
That silver swelling on the air hose houses an air filter that removes some moisture. The manual says to change it every 2-3 hours of operation and a couple are provided in the parts that accompany the compressor.
BB
B.B.
Well how helpful is this really???
You need a power source, lots of the brass disks that blew in yesterdays blog, and now a supply of moisture filters. And what else?
Sounds like you would need a support truck to keep this going while on the move.
-Y
Yogi,
This is very helpful for those considering entering into the game changing world of pcp’s.
You sound a lot like me before I entered the pcp world. I was put off by the “accessories” and their cost to support a pcp. I kept objecting to the amount and cost of “support equipment” and was successful at justifying my avoidance into the pcp world for a long time. This was a long time ago and my evolution at that time ended with an expensive compressor and expensive multiple carbon fiber tanks because these were the best options. That has changed dramatically.
These small compressors that are portable eliminate the need for these extreme expenses. This is a game changer to be able to enter the world of pcp’s.
Yogi,
Bursting a burst disc is a very rare occurrence. Having an extra one takes no room and weighs nothing. I would recommend as Jeff did, that you buy a high pressure water separator and install that in your initial setup. It should be considered as part of the cost of buying the compressor. Buying a large 4500 psi carbon fiber tank and having it filled locally is a more sure way of having clean dry air if there is a local place that will fill it at a reasonable price.
The way I got into PCPs was to first save up enough money to buy my carbon fiber tank. Only after I had my tank did I consider getting a PCP airgun.
David Enoch
David Enoch,
Dittos!
No maintenance headaches and the LIFECYCLE costs are hard to beat.
The problem is finding the Dive Shops, Firehouses, and Paintball Stores that are within reasonable range and not off-putting by made up regulations or poor hours in the off season.
shootski
David,
If bursting a disk is a rare occurrence, then I would not remember where I put them when I needed them.
One more things, and another, and another….
-Y
Thanks for the primer on compressors. Interesting stuff. That’s why I love this hobby. So much to learn on such a variety of topics.
BB,
With the touting of compressors for PCP airguns, the two items that must be carefully monitored are the desiccant and the filter that remove moisture and debris from the air supply coming out of the compressor. Putting dirty or moisture-laden high pressure air into your precious PCP will render it inoperable in a few of years of moderate use, because moisture causes corrosion of the internal components and oil will gum up the operation of those internal components. I have seen valves corroded shut and regulators plugged with oil, on inoperative guns I have worked on. The newest one was a 3 year old PCP that was shot daily by its owner.
If you buy a cheap compressor, purchase a good water separator with desiccant (molecular sieve) to remove water vapor, and then change that desiccant media out at regular intervals. Second, change the filter media (cotton) regularly too, because over time it will become saturated with moisture (that you are trying to remove) and with oil vapors that get past the piston rings of the compressor. These will be a recurring costs like oil changes for your car and should be done after a certain number of hours of compressor run time that you can figure out by perusing the interweb.
Careful attention to desiccant and filters are required for cheap or expensive air compressors, but most expensive compressors (Bauer, Alkin) come with good water separators and filters already that you don’t need to upgrade; only maintenance is required.
I want to reinforce what Cloud9 said here – when compressing air with a powered compressor, you really need to have an air drier in the path to your gun or tank. That means an appropriate desiccant filter, as only a desiccant will pull the water vapor out of the air stream. A simple media filter is great for catching water droplets, but it won’t pull vapor out of the air (if it did, that roll of paper towel in the kitchen would get soaked just sitting out in the open).
People often think that since they run their compressors in an air conditioned or dehumidified room, that there will be no issues. This is just flatly wrong – all it does is reduce the amount of liquid water one gets from compression; it does not prevent water vapor from being in the compressed air. The relative humidity level that it would take at room temperature for our compressed air to be fully “dry” after compression would be about 1% – something nobody will achieve around here (it is typically a bit under 10% in the hot desert, and goes up as the air cools down).
Air holds less water vapor as the temperature drops, and as the pressure rises. When we use powered compressors, the air charge gets hot enough for it to carry water vapor in it through the hose, and when this air charge later cools down to ambient, the water vapor will condense out into liquid water – in the reservoir. This is the effect of a “dew point” – when it went into the gun, the water was a vapor, but as it cools down, it condenses into small drops in the reservoir. Over time, these small drops build up into a problematic amount of liquid water.
This does not happen when one uses a hand pump, at least correctly – running about 50 strokes or so, then venting the line and letting it cool down before continuing. Each stroke has a short “dwell time” sitting in the base of the pump in which it cools down (the base absorbs the heat) and the water condenses out before moving to the gun. This naturally helps to keep the amount of water vapor passing into the gun low.
But with a powered compressor the air charge gets hotter the longer the pump runs, and thus the ability to carry vapor goes up.
I could get into the numbers and math, but I’ll spare you. Just use a desiccant filter with these pumps. Eventually you will be glad you did . . . .
Cloud 9
Before I say anything else please know I respect your obvious expertise and experience. But I’m not doing the maintenance for moisture control you describe. Rather I’m putting a drop (or two at the most) of non petroleum oil in the PCP’s fill hole every other fill. I’m depending on the oil being blown out the barrel when shot after doing its job of preventing corrosion in the gun’s air reservoir. I hope Shootski, BB and even Gunfun 1 will chime in.
See my comments yesterday about my gun fill only compressor. Time will tell the rest of the story. I should point out that I expel air in the compressor both before filling and after filling just as I did when I used a hand pump. Also I keep my compressor indoors, operate it outdoors but avoid using it when outside air moisture is high.
Deck
No worries Decksniper. The oil you are adding will coat all of the internal parts and prevent corrosion which is good, but it’s viscosity will affect the regulator operation repeatability and the speed at which the exhaust valve will open and over time the oil will coagulate and cause internal components to stop moving. These effects will show up as shot to shot inconsistency and in extreme cases as muzzle velocity reduction.
What you describe is exactly what is done for multi-pump air rifles, Sheridans for instance.
Cloud 9
Thank you for your response. In your opinion will the exhaust valve opening and closing speed of a multi pump airgun suffer from Pellgun or similar oil being applied to the tip of fresh CO2 cartridges?
Deck
Cloud 9
Oops! My brain valve slipped. My question refers to CO2 guns but come to think of it, multi pumps too get Pellgun or similar product in the innards at least by me.
Deck
I don’t believe that little amount of oil will make a difference
I bought a used 100 cu. in. cylinder with a fill assembly and hose off of a classified ad, $200 got it to the door. The Y-H compressor ($300 and change seasonal sale) will fill it to about 4200 (who knows with these little gauges?) in about 4 or 5 minutes from 2700 or so. I have a gold vertical moisture trap I installed on the side of the compressor (Amazon purchase) I put a freezer cold pack on it and fill the cylinder. My Navy experience, systems used chillers in addition to desiccant to dry compressed air. I get some moisture out of the trap, not a lot. I haven’t had any moisture issues since I’ve been using this setup, but I did have to replace the cylinder and pressure gauge block on my Marauder, filled with a Hill hand pump prior to the compressor, due to corrosion. The new tube on the Marauder is now pretty well treated with silicone oil to slow the effects of possible moisture.
I get several refills from the cylinder on a day(s) plinking from Marauder or a couple Gauntlets. I like the once in a while start the compressor for a few minutes, vs the more frequent on-off cycle of a direct fill (and as mentioned, silent, quick fill from the cylinder).
MMCM13,
Sounds like you have a good and economical solution. In my opinion, your solution is preferable to a compressor that will only fill guns.
David Enoch
MMCM13,
Interesting experience.
You wrote: “…I did have to replace the cylinder and pressure gauge block on my Marauder,…”
Did you have any corrosion on the gauge block anywhere that is actually inside the pressure vessel?
That Crosman design has a large portion (between the O-Rings) that is in fact outside the pressure vessel and is exposed only to ambient conditions. Most of the photographs of this part shows corrosion on that part of the block only…someone please find a few undoctored images if you want to prove me wrong. IF they exist it probably is someone who didn’t use a VERY SMALL amount of CHAMBER OIL or similar and who has worked, or had someone work, on their airgun and contaminated the gun with, dirt, body oils, and salts! As far as regulator and valves getting gummed up that is TOO MUCH lubricant and TOO MUCH dirt and contamination introduced in some way into the fill point-to-discharge point path of the airgun.
Regulators often require some form of lubricant to function correctly see owner’s manual for your model. Do we all know someone who thinks and says: Well if a little is good…MORE MUST be better. Or, Ooops that was more that came out then i expected? You don’t know someone who has said that! You should consider yourself blessed.
Please note that i am not here to keep you from buying an effective drying system i’m just trying to provide some FACTS and experience about pressure vessel, valve, and regulator corrosion.
First and foremost you need a clear understanding of FILL SYSTEM PURCHASE COST, OPERATING COST (to include maintenance and consumables) and finally LIFECYCLE COST which is the real key to your decision.
You cannot compare fill systems without understanding those costs.
As far as corrosion: clean pure water by itself provides a very weak source for initiation. If however you add contaminants like salt and skin oils the corrosion possibilities are/become astronomical.
Decades of PCP experience and the mentorship of the likes of Dennis A. Quackenbush and even the Godfather of Airguns…mostly about Spring Pistons…but he has learned a great deal over the years since about PCP fill systems and has shared it right here on his BLOG.
Ask questions and please don’t blow SMOKE by repeating INTERNET/You Tube “WISDOM” without verification.
shootski
What was the internet repeating part? I stated my experience. I spent 25 years in submarine engineering, I have experience with hp (4500 psi) air systems and cleanliness requirements. I have a solid background in physics. I believe I have a good understanding of how the Marauder air rifle functions and where its pressure boundaries are. I have training and experience in corrosion control in shipboard systems. I made no claims about anyone else’s experience.
I have wondered why there were an only a dozen or two active members on this blog, I don’t now.
MMCM13,
Sorry if my reply put you off.
I should have made it a stand alone or far clearer when i was directing my comments to the general readership.
I will try harder to avoid anything like this happening in the future.
shootski
And this is one of the big reasons I like this blog. Civility. People say stuff, others could get mad, but we value the blog and our relationships to others more than offending each other. So we take a deep breath, and stay respectful. Usually it turns out to be a misunderstanding anyway.
B.B. (and experience PCP Owners)
I haven’t went to the dark side. I’m very confused on this whole water/moisture in the air. Some say you must have a filter. Yet when I look at say the Hill Hand Pump, isn’t it’s filter in the air inlet (not the output side)? If so, yes it would be drier but with the heat coming from the compressing of air, wouldn’t there still be moisture going in the gun? Next, I was with the thinking that Decksniper said above. I would think you could put a drop or two of silicon in the fill nipple (probe) of each fill. Wouldn’t that work? Kind of like a larger version of what is done to C02 guns. I’ve never heard of thought of oil gumming up a regulator. So if I was to buy a non regulated gun, then that wouldn’t be a problem then? If or when I go to the dark side, I’ve thought of a lower fill PCP so I could use a hand pump (or just for a faster, easier fill for a small compressor). Also one without a regulator because I understand those can and do go bad? From what I’ve read from BB on most non reg PCP, if you stay without a certain psi range for the gun, it’s pretty consistent?
Thanks All
Doc
Hello? Any help on my questions/Comments?
Doc Holiday,
What Cloud 9 said about filters is absolutely true and has nothing to do with moisture removal. A filter after the compressing device protects your airgun a filter before the compressing device protects the device from dirt and other debris.
Moisture is an indirect issue and actual elimination of it totally is difficult; it can be reduced in various ways.
Dive Shops use very expensive fill systems and often have a Cascade System of Storage cylinders each with filters and moisture traps with purge valves to dump the condensed water. The last cylinder in a Cascade Series of many cylinders has the driest and cleanest air and that is used to fill your cylinder.
Regulators come in many different designs and are made of various materials. Some materials are considered self lubricating and the manufacturer will indicate NO LUBRICATION. Other Regulators require specified lubricant(s) to operate correctly. Yes they fail but have been getting better.
Valves can and should be designed to be balanced over a known range of pressure, projectile Mass/shot cycle energy required input.
Books can be written about this/these topic(s) and some few have been.
B.B. recommended a Benjamin Discovery type airgun as an outstanding first PCP for a reason, relatively low pressure, not much to adjust so KISS, and i fully concur.
Keep asking questions Orv!
shootski
Yogi,
I think it is less common for a burst disk to rupture that for a mainspring breaking in a springer. Yeah, when it happens it is a problem but not common enough in my experience to worry about keeping a spare. By the way, you can tape that extra burst disk to the compressor with a piece of clear packing tape so that it will be there if it is ever needed. I have had 4 compressors and never burst a burst disk. My only experience with a failed burst disk came from a CO2 hangy bottle for my Crosman Mk1 LD that ruptured behind me when the sun moved and the bottle got too hot. Boy, did I jump!
David Enoch
David,
Had that happen with the C02 on the paintball field. Yes we all jumped. Like a firearm went off lol
Doc
There has been mention of additional filtering of compressor air. I added a charcoal and cotton filter to my large compressor output. It also has a moisture trap section. This is in addition to the filter built into the compressor. With this additional filter, I do not feel the need to be concerned with moisture or particulates in my CF tank.
I would not mind putting an additional filter as on these small compressors on the output of my CF tank. I will take all of the filtration I can get.
I also like adding a couple of drops of silicone chamber oil every few fills. It helps to prevent small leaks. Yes, too much can cause issues, but it is better than rust.
I guess now I know why you see a lot more Turkish PCPs than Greek PCPs.
The Greeks add olive oil [vinegar, Windex] to EVERYTHING!
;o)
BB
Anyone considering buying their first PCP that reads this report has got to be wondering if it is a good idea. There are two different schools of thought about moisture control. Surely companies have done rigorous testing. It would be useful to know the results of such tests. Funny thing, I use far more synthetic oil on my CO2’s and multi pumps than ever touches the fill hole of my PCP’s.
If I were the owner of a company that sold both PCP’s and the auxiliary products to maintain them I would be asking is it more profitable to sell more PCP’s or more auxiliary equipment.
I’ve said too much I reckon.
Deck
Interesting topic!
So far, I have only three dark siders. They can be filled with the hand pump which I additionally equipped with two stage cotton filter on the output. The moisture is not so big topic regarding hand pump used slowly and cleaned from time to time – I’m glad the general discussion here confirms that!
After I went to 36FPE+ in .22 Stormrider nonregulated, with modified spring to get the maximum out of it (it is 10FPE more than in the spec!) I get only 5 really good stable shots, we can say one magazine 7 shots per fill makes sense. That was for me an eye opener to understand why you need an air compressor using stronger PCP. With the cal .177 F-version nonregulated set up to approx. 5FTE will give you 50 really good shots and approx 80 usable shots per fill. That is a difference – to pump once in 80 shots or to pump each magazine after 7 shots!
I thought to buy some cheap available compressor like this in the blog. This is a great blog to ask questions and to see all behind it – is it worth for me or not? What do I need to consider when I will go after it?… The background is to have something more powerful where you need the air, the pump will not be there as a possible solution anymore.
Against the moisture issue – when you are not able to feed the air compressor with very cold air you will always have it.
The question for me would be: what is NECESSARY against the moisture to connect to a cheap compressor?