Air Venturi air compressor: Part 1
by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- The problem
- Air Venturi compressor
- Temperature gauge
- Pressure gauge
- Oil lubricated
- Fill hose
- The test compressor
- First time operation
- I am impressed!
Today I start a report that’s going to have a major impact on your airgunning world. Even if you are a dyed-in-the-wool spring-gun user, this report should have an influence on how you view the world of precharged airguns.
Precharged pneumatic guns work by storing a large supply of compressed air that they use in measured amounts with every shot. They are the oldest type of airgun — dating back to the middle 1500s, we think. And the challenge has always been how to get compressed air into them.
I’m not going to give a lot of history today, because I want to get right to the point. So let me bring you up to speed. The challenge has been to produce a high-pressure compressor that compresses air to 4,500 psi in a reasonable amount of time, and to make that compressor as easy to operate as possible, because the people who use it will have little to no prior knowledge of compressors. All of that must be done at a price people can afford.
The problem has been heat. When air is compressed, heat builds. At the pressure we are talking about, heat builds rapidly to the point that things like seals can’t take it and start failing. The military solved the problem many years ago by throwing money at it. The three-cylinder compressors found in bombers and some tanks (to power onboard pneumatic systems) are extremely effective at dissipating heat. Their cylinder heads are finned and made of material that acts as a heat sink, to draw the heat away. If you have $10,000 to throw at the problem, you can do it this way, too. Better yet, you can buy a surplus air compressor from the military for as little as $1,400, and you are almost done. Of course it will weigh 150 lbs. and will require a massive conversion to get it to run on AC current (they come set up for 24-28 volts), so better figure on a total of $3000 to be safe. When I got into PCPs, that was almost all that was available.
I could go on and on, but I really don’t want to. I will if you force me, and believe me — I do have the stories — but can we all just agree that compressing air to 4,500 psi is not easy, and let it go? Please don’t play dumb and wonder if a shop compressor can do the job, because it can’t. We are talking about air pressure that until the past 10 years was in the realm of the exotic to impossible for the average person.
Air Venturi compressor
Enter the Air Venturi air compressor. This is a 76 lb. home unit that will fill a carbon fiber air tank very rapidly. It’s the size of a small cooler. When I say it works very rapidly I mean that in comparison to anything else that is on the market at or very near to the same price. AirForce Airguns has a much larger shop compressor that is faster, so if you have $10,000 to $14,000 to spend, that’s the way to go. The Shoebox Compressor can fill your tank, as long as you have the time to do it. Plan on a few days, if you want to be around to watch it as it is filling.
I have owned and tested home air compressors since the first one, made by FX (a Swedish manufacturer of PCPs and hand pumps), hit the scene in the late 1990s That one used a hand pump mechanism that was automated with a motor, and many compressors still use that design approach today.
The FX compressor made many years ago was one of the first made for home use. It used a hand pump mechanism at its heart. It only pressurized to 3000 psi.
I was surprised to see that the Air Venturi unit does not have a hand pump at its heart. It has two real cylinders, just like compressors that start at $2400. It also has a full control panel that includes separate switches for the cooling system and compressor. The cooling system is turned on before starting the compressor and if it won’t turn on, the compressor will not start. And it has one more gauge that I’ve never seen on another compressor. It’s a gauge that I never want to be without, now that I’ve seen it in action.
This compressor has a temperature gauge! It isn’t even labeled on the test compressor I am using, but it didn’t take a genius to figure out what it is. I told you that heat is the enemy of the seals in compressors so a temp gauge is a wonderful way to monitor things.
The temperature gauge tells you the temperature of the cooling system, I think. When this picture was taken the compressor was not on and was sitting in my 60(ish)-degree F, garage. Gauge reads 16.4 degrees C which is 62.8 degrees F.
This compressor runs on 110-volt 60-cycle AC house current. There is no provision for any other current at this time. I’m running it on a 20-amp household outlet and there is a 6-foot extension chord between the compressor and the outlet.
The compressor is water-cooled and the user services the water level. It holds about 5 quarts of water.
There is a large dessecant air filter in line with the air intake. The compressor does not have a water vapor purge that operates while it ius running, but when the bleed valve is opened after filling, water vapor is blown out.
The user sets the desired fill pressure on the pressure gauge, not to exceed 4500 psi. Then the machine is started, and when the pressure rises to the set point, the compressor turns off.
Set the desired fill pressure by pushing in on the red button and turning the needle it moves to the desired pressure. When the larger fill needle contacts the set needle, the compressor switches off. The cooling system still runs, though. This gauge is labeled in both bar and pounds per square inch (psi).
This compressor is lubricated by oil. I mention this because all the compressors on the market lubricate differently. The ones that use a hand pump use grease. My Omega SuperCharger uses grease. But the compressors with conventional pistons all seem to use standard compressor oil that can be bought at any automotive store, and the Air Venturi uses either that or 5W40 motor oil. It holds 1/3 of a quart of oil, and a sight glass tells you instantly where things are.
The fill hose is permanently attached to the compressor and ends in a 4500 psi female Foster fitting. You can fill many airguns directly with just this hose, but if you have a carbon fiber tank, its hose probably ends with a female Foster fitting, as well, so you need a Foster male to male adaptor.
The test compressor
The test compressor has been around a long time. Pyramyd Air tested it thoroughly, then they loaned to to an airgun writer to test. It came to me with a lot of use on it, but I read the manual and was able to put it into operation right away.
First time operation
The first time I used it, I filled a 98-cubic-foot carbon fiber tank (yes, the tank is larger than my normal 88 cubic-foot tank) from 3800 psi to 4500 psi in about 15 minutes. Folks — that’s flying for a home compressor! My Omega SuperCharger would take at least an hour to fill the same amount.
The temperature rose quickly (5 minutes) from under 20 degrees Celsius to about 60 degrees, then it leveled off. At the end of the fill the temp was 64.4 degrees C. After I switched off the compressor (and left the cooling system running) the temp dropped about 15 degrees in 15 seconds. Then it declined more slowly. After 15 minutes the temp was down to 23 degrees C and I switched off the cooling system.
When I bled the line before disconnecting, the compressor exhausted a large amount of water vapor from the air filter. The purge was long enough to give me confidence there is nothing left behind.
I am impressed!
I’ve never seen a home compressor that works as well or as fast as this one. Sure, the compressors that cost $3000 work that fast, but they aren’t much faster, and their maintenance is far greater. This one requires you to watch the oil and water levels and that’s it. Right now I am thinking about buying this one for my personal use.
My plan is to test the compressor very thoroughly for you. Yes, Chris U.S.A ., there will be more pictures. I will show you what’s behind the curtain.