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Homebuilt PCP pump

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Homebuilt PCP pump

Unread postAuthor: ToasT » Sun Nov 03, 2019 4:00 am

So, I moved to a bigger property, which has many places to shoot that are no where near a power point for the old fridge compressor. I don't fancy lugging a generator around or dealing with high pressure air, so I made a hand pump.

The pump is a 20mm copper pipe brazed into a 20mm fitting with a custom checkvalve built into that fitting. I aimed for 0 dead volume in the pump to improve efficiency and the maximum pressure that can be reached and think I have got pretty close to achieving that. The piston uses a double floating o-ring with a few ports to aid 'recharging' the pump on the up-stroke.

But pictures are where it's at right?
These (along with image comments) should be detailed enough for anyone else to be able to make their own, lathe recommended.

1.jpg
Exploded view of check valve internal components.

2.jpg
Another view of check valve internals.
The ridge half way up the left part is not required, it was used to position the top surface of the checkvalve half way through the 20mm fitting.

3.jpg
Top view of check valve, the copper tube is soldered in to meet this surface
The copper tube meets this surface and is soldered in place, when the iron reducing fitting is threaded on it sandwiches everything together. This allows for any part to be accessed and serviced if needed in the future. Also while we are at this point, I flared the end of the copper tube ever so slightly as this is not a brazing fitting so is slightly over sized, this shuts off the gap preventing solder from flowing down into the check valve area.

4.jpg
Piston, showing floating o-ring and cuts/holes acting as the 'recharge' ports. Also showing the end cap

6.jpg
End cap, acts as a guide to keep the piston and threaded rod square.

5.jpg
Final assembly


Still need to make a proper handle and foot plate. I have used square sided fittings partly because that it what I had, but also to make fixing to a foot plate easier.
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Re: Homebuilt PCP pump

Unread postAuthor: jackssmirkingrevenge » Mon Nov 04, 2019 5:57 am

Looking good! My one concern would be the threaded rod rubbing against the endcap that will wear over time.
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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Re: Homebuilt PCP pump

Unread postAuthor: ToasT » Tue Nov 05, 2019 5:14 am

jackssmirkingrevenge wrote:Looking good! My one concern would be the threaded rod rubbing against the endcap that will wear over time.


Yea that will definitely happen. I could fill in the threads with epoxy to minimise the wear, but I'm happy to treat it as a sacrificial part as its easy to make another. It should last a reasonable length of time, but I guess I will find out.
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Re: Homebuilt PCP pump

Unread postAuthor: jackssmirkingrevenge » Tue Nov 05, 2019 7:23 am

ToasT wrote:I'm happy to treat it as a sacrificial part as its easy to make another.


The T-34 of airgun pumps :) that sounds about right!
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