supercharged pumper

supercharged pumper

Joined: September 25th, 2006, 2:19 pm

February 20th, 2012, 3:00 pm #1

A couple years ago I scratch built a pumper and have dedicated it to bench rest for smooth bore expiriments. It is a .25 cal and has a 30" smooth bore barrel. The exhaust valve is inline and blow open. The pump volume is 2.6ci so thats a pump tube diameter of 5/8" X 8 1/2" sweep. The pump handle is 19" long. The reservoir is quite large and it generally takes 25 strokes to send a .25 cal JSB Exact King 25.4 grainer out at 875fps plus.
When I built this gun, I designed the air intake hole for the pump to be a 1/16" hole thu with a 3/16" counter bore anticipating future experimenting such as I describe.

Well, this weekend I FINALLY came upon a neat little 12 volt air compressor at the local secondhand store. Set me back $3. Removing the compressor unit from its plastic case, I discovered a compact piston compressor driven by a small DC motor which has a 3/8 gear in the motor shaft that runs against a 1" nylon bull gear on the compressor.

The unit has a gage on it and will easily pump to 60psi. I removed the cigarette lighter adaptor from the cord and found the compressor to run well using a 9.6 volt rechargable battery. Next I coupled a length of 3/16" vinal tubing to the hose of the unit. Now I am in business.

End of story is that by precharging the pump tube, ~45psi near as I could determine, I could now fill the gun in four strokes instead of 25.

So I am thinking. To hell with the multi-stage pumps which are generally minimal swept volume and o-ring intense. If the tiny air compressor and battery were concealed in the buttstock, I think one could get many shots per battery charge and greatly minimize pumping strokes.
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Joined: April 28th, 2010, 12:23 am

February 20th, 2012, 3:26 pm #2

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Joined: September 25th, 2006, 2:19 pm

February 20th, 2012, 4:20 pm #3

You can up the capacity and reduce pump strokes with any pumper provided that you have a means of injecting good volume of air into the pump.

The unique intake port on my do-it-yourself pumper made it easy peasy for a down and dirty experiment. Here is a diagram of the tool I made to coin the 1/16" intake port.

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Joined: April 28th, 2010, 12:23 am

February 20th, 2012, 7:54 pm #4

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Joined: April 28th, 2010, 12:23 am

February 20th, 2012, 8:13 pm #5

You can up the capacity and reduce pump strokes with any pumper provided that you have a means of injecting good volume of air into the pump.

The unique intake port on my do-it-yourself pumper made it easy peasy for a down and dirty experiment. Here is a diagram of the tool I made to coin the 1/16" intake port.

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Joined: September 25th, 2006, 2:19 pm

February 20th, 2012, 9:30 pm #6

The battery is from a portable 9.6 volt drill I had which went bad so I saved the bat and charger. I think a battery pac from an RC would be more compact and just as reliable

Keep in mind that I do not have the compressor mounted in the gun. Next order of business is to solder a more permanent recepticle to the air tube for hose connecting. Then I can do some good trial tests to better answer your question. The pump seems not to work to hard and I may remove the gage and rig a relief valve to the circuit.
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Joined: March 1st, 2002, 12:22 am

February 20th, 2012, 10:28 pm #7

You can up the capacity and reduce pump strokes with any pumper provided that you have a means of injecting good volume of air into the pump.

The unique intake port on my do-it-yourself pumper made it easy peasy for a down and dirty experiment. Here is a diagram of the tool I made to coin the 1/16" intake port.

So your using the electro-pump to charge the pump tube, then pump that charge using the gun's pump arm?

 

and your drwawing shows how you can form the hole the pump connects to?

 

 


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Joined: September 25th, 2006, 2:19 pm

February 20th, 2012, 11:15 pm #8

The air intake hole is what I already have on the gun. The counter bore fits well with the 3/16 plastic tubing running from the compressor.

Reason I showed the tool is because this method of creating the air intake port is easier for me than that which many pumpers have. For instance, I have a Crosman 2100 and its air intake configuration would be difficult to seal for the precharging.
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Joined: November 28th, 2002, 6:26 pm

February 21st, 2012, 3:46 pm #9

A couple years ago I scratch built a pumper and have dedicated it to bench rest for smooth bore expiriments. It is a .25 cal and has a 30" smooth bore barrel. The exhaust valve is inline and blow open. The pump volume is 2.6ci so thats a pump tube diameter of 5/8" X 8 1/2" sweep. The pump handle is 19" long. The reservoir is quite large and it generally takes 25 strokes to send a .25 cal JSB Exact King 25.4 grainer out at 875fps plus.
When I built this gun, I designed the air intake hole for the pump to be a 1/16" hole thu with a 3/16" counter bore anticipating future experimenting such as I describe.

Well, this weekend I FINALLY came upon a neat little 12 volt air compressor at the local secondhand store. Set me back $3. Removing the compressor unit from its plastic case, I discovered a compact piston compressor driven by a small DC motor which has a 3/8 gear in the motor shaft that runs against a 1" nylon bull gear on the compressor.

The unit has a gage on it and will easily pump to 60psi. I removed the cigarette lighter adaptor from the cord and found the compressor to run well using a 9.6 volt rechargable battery. Next I coupled a length of 3/16" vinal tubing to the hose of the unit. Now I am in business.

End of story is that by precharging the pump tube, ~45psi near as I could determine, I could now fill the gun in four strokes instead of 25.

So I am thinking. To hell with the multi-stage pumps which are generally minimal swept volume and o-ring intense. If the tiny air compressor and battery were concealed in the buttstock, I think one could get many shots per battery charge and greatly minimize pumping strokes.
...can you help me out with the arithmetic? I don't understand how 4 stroke volumes of (45psi + 14.5psia)/14.5psia = 4.1bar air, can be the equivalent of 25 strokes of 1 bar air.

That is to say 4 x 4.1 = 16.4 doesn't seem to equal 25 x 1 = 25.

Are you sure your supercharge pressure isn't higher than 45psi (i.e., more like 72psi = 5bar)? If so, what am I missing?

Steve
Last edited by pneuguy on February 21st, 2012, 4:18 pm, edited 1 time in total.
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Joined: September 25th, 2006, 2:19 pm

February 21st, 2012, 8:08 pm #10

and you are correct in doing so. The numbers don't match.

Getting into the project more extensivly this morning I really do have questions about that cheaper than cheap Chicom gage. At the moment I have only the stalling sound of the compressor to go by, but I fixed a tire pressure gage to the circuit and it immediately went to the peg which reads 60psi. Therefore considering yrecanting claim.
If it were faulty gage, that might explain why the 4 strokes were a real son-of-a-butch.
Especially when the greatest effort applied to the lever is not as the handle nears the tube but approx 30-40 degrees before hand.

I think there is another facet to supercharging. That is to say that head space loss per a low number of supercharged strokes will net more valve pressure than a high number of normal strokes. Would you please comment on that?
Although such would not give complete explanation, but is meaningful, to the claim of 4 super strokes @ 45psi precharge being equal to 25 normal strokes.

I am currently in the process of rigging a better plumb job which will run from compressor to tube. Also will discard the gage and install a relief valve for consistancy. Therefore more realistic numbers should be forthcomming.
Thanks
Ron
Last edited by oo7fuzz on February 22nd, 2012, 2:04 pm, edited 1 time in total.
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