Pneumatic Pnews

Monday, April 17, 2006

What about a hand pump?

by Tex Force

You've finally convinced yourself to get a precharged pneumatic air rifle, now you have to decide how you're going to fill it. The two most common ways are from a scuba tank or with a hand pump. Let's take a look at the hand pump to see what it involves.

Can you REALLY pump 3,000 psi by HAND?
The hand pump looks a lot like a bicycle pump, but it's really very special inside. It's not just one pump but three - or rather it compresses air in three separate stages, which is how it is possible for a person to compress air to 3,000 psi (pounds per square inch). A shop air compressor goes as high as about 175 psi, and portable paint sprayers get up to 125 psi - so 3,000 psi is way beyond any of them. There is a device you can attach to a shop compressor that will multiply the air output to 3,000 psi, but it costs about $800 to $1,000. Nothing on the market is even close to the low price of the high-pressure hand pump!

It works by mechanical advantage
If you've ever lifted a car with a hydraulic jack, you know something about mechanical advantage. You can lift a tremendous weight that way, but it takes a lot of pumping, because each stroke only does a small amount of lifting. So it is with the hand pump. Depending on the volume of the reservoir you are filling, the hand pump takes from 8 to 14 pump strokes to increase the internal pressure by 100 psi. The AirForce air tank (second item down) is one of the largest tanks in airgunning, and it takes from 12 to 14 pump strokes to boost its pressure by 100 psi. If you want to put 1,000 psi into the reservoir, it will take 120 to 140 pump strokes. That's about a five- to seven-minute session.

You don't start from zero each time
Precharged guns are never shot until they are empty. You shoot until they are no longer satisfactorily accurate. For many guns, including all three AirForce models, there will still be something like 2,000 to 2,200 psi left in the air tank at that point. You need to put back only 800 to 1,000 psi. Airforce tells their customers that, depending on the power setting they use, they will need to pump from one to two full pump strokes per shot. That's a fair guesstimate, though with the guns set at the most powerful level, the number may be above two strokes.

How hard is it?
Until 1,500 psi, most adults can pump the pump with one hand. It is very light up to about 2,000. Somewhere around 2,200 to 2,500, you will notice the effort becoming greater and above 2,700, it is the hardest. Most people pump with their arms until the effort increases, then they stiffen their arms and use the weight of their body. As long as you weigh more than 140 pounds and have reasonably strong wrists, you will be able to reach 3,000 psi. Lighter shooters sometimes rest their stomach on the pump handle and make the pump try to support their weight, but shooters over 150 pounds shouldn't have to do this.

Does the hand pump remove all the moisture from the air?
No - the hand pump still permits a small amount of moisture to enter the reservoir it is filling. A scuba tank has drier air, but even then, there is always a small amount of moisture in the air. In the ten years hand pumps have been in worldwide use, they have not proved to be a problem in this respect. Incidentally, one type of pump has a moisture filter on the intake side of the pump, where it does almost no good. The only effective moisture filter is thermal mass inside the high compression chamber that all pumps on the market currently use.

How long will a pump last?
A pump operated correctly should last more than a decade with no maintenance. If it is abused, it can fail within a month. The biggest abuse is not allowing the pump to cool down after each five-minute pumping session. The final compression stage gets extremely hot (over 400 degrees F) and will fail early if not allowed to cool for 15 minutes between sessions. I always bleed the pump between sessions to help cool it.

Bleeding the pump means exhausting the high pressure air so the gun or reservoir can be disconnected. Proper bleeding is the other maintenance factor. Always bleed using the brass screw at the base of the pump. If you have a second bleed screw on the fill gauge, do not use it. The pump needs to have the high-pressure air blow out the collected moisture from the compression chamber every time you bleed it.

The hand pump is a great way to fill a precharged airgun if you're not averse to a little work. It lets you go into the field without a heavy scuba tank, plus it is the source of high-pressure air whenever you need it. If you operate it according to the instructions, it should give a long period of good service.

1 Comments:

  • Excellent blog!
    The use of the scuba tank is certainly convenient but the hand pump is a very good source of aerobic exercise and most of us need that sort of thing on a regular basis. I think the precharged airgun is the ultimate in adult airgunning although the only one I own is a Talon SS with an extra 24" .22 cal barrel. It's good for target practice and serious varmint control and it also looks cool.
    CWI

    By Blogger airgundoc, at 7:31 AM, April 17, 2006  

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