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Homemade or store-bought?

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Homemade or store-bought?

Unread postAuthor: Gun Freak » Wed Sep 01, 2010 6:19 pm

I found this really nice 3 stage 260 psi floor pump on amazon which I would be able to get for under 50 bucks. But I also have the option to build a stirrup pump. I hope to get 400 psi on small volume, like pengun volume, which I think I can get out of the Topeak pump but I know for sure I can get it with a homemade pump. I also want to take in consideration ease of the stroke and the volume of the stroke. The Topeak is three stage so I think it will be a breeze to pump things up relatively quick, but I'm not so sure about a homemade stirrup pump. Thoughts?
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Unread postAuthor: clemsonguy1125 » Wed Sep 01, 2010 7:42 pm

Your probably gonna spend 50 bucks for the stirrup so price is about equal. If you want 400 PSI the Sitrrup will be better and easier I believe. The Topek is made for 260 PSI so at 400 you risk blow an oring or causing leaks. My opinion is to build a stirrup.
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Unread postAuthor: saefroch » Wed Sep 01, 2010 8:15 pm

Build a stirrup. Why would you want a 3-stage for pengun volume? Even if you're taking it beyond that... just stay with whatever pump you have and build a stirrup to go past whatever pressures you can reach right now. With the right materials, a stirrup can hit incredible pressures.
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Unread postAuthor: Technician1002 » Wed Sep 01, 2010 10:26 pm

A multi stage pump is much more efficient. It is less critical of dead space as each stage will output through the check valve with ~20% pump stoke remaining. Trying for high pressure in a single stage requires a compression ratio in excess of 10:1 before the check valve opens. This minimal dead space is difficult to achieve in a home built pump. The air in the dead space re-expands on the piston return reducing the intake volume. A multi stage pump mostly eliminates that loss for high efficiency delivering high volume at high pressure. Multi stage is highly recommended for outputs greater then 10 BAR. It is pretty much required for pressure above 15 BAR.

So in summary, stirrup pump for up to 100-150PSI, multi stage to get reasonable volume for >200 PSI.

What pressure are you wanting to reach?
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Unread postAuthor: Gippeto » Wed Sep 01, 2010 11:36 pm

Technician1002 wrote:Trying for high pressure in a single stage requires a compression ratio in excess of 10:1 before the check valve opens. This minimal dead space is difficult to achieve in a home built pump.


Errm....

The stirrup pump in the tutorial has a compression ratio of over 100:1, easily accomplished.

For a lightweight like GF, you're going to have to use tube with a smaller id. to get to 400psi. :wink:

Edited by jrrdw, fixed quote tags.
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Unread postAuthor: Gun Freak » Thu Sep 02, 2010 7:29 pm

The pump won't only be for a pengun lol, I was planning on a relatively high volume pump for my golf ball cannon and also a quick way to pump up my airsoft bbmg tank. So the actual pressure I will need at max is 150. I guess the 3 stage pump is a little overkill then. A stirrup should do the job but I am worried that the volume will not be high enough and I don't want it to take forever to pump up my gun. I know it has a huge chamber but I think I can cut down the pump time by half from my existing bike pump which is a piece of crap.
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Unread postAuthor: saefroch » Thu Sep 02, 2010 7:55 pm

Well if your max pressure is 150, I'd just get yourself a robust bike pump with a gauge that goes to 150, mine goes to 160, but the pump itself is rated to 250. A stirrup pump will take you a while to fill a large tank, calculate out the displacement on the pump and compare that to your golf ball cannon's chamber. A three-stage would be good if you're taking a very large chamber to 250+. But you mentioned in the original post you wanted to hit 400... Now you're saying 150?
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Unread postAuthor: Gun Freak » Thu Sep 02, 2010 8:12 pm

I wanted to hit 400 with a pengun volume which I think is possible with the three stage and a stirrup. The big thing was stroke volume or whatever you want to call it. I didn't want it to take forever to pump up my gun. The target pressure here for a large volume will be under 150.
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Unread postAuthor: Lockednloaded » Thu Sep 02, 2010 8:41 pm

why not just buy the three stage and a small shock pump?
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Unread postAuthor: Mr.Sandman » Thu Sep 02, 2010 9:24 pm

2 words, Fridge compressor. They have relatively good flow for their size and can take you to any pressure you desire. And they are cheap if you know where to look. It also eliminates any work effort to pump up your cannons.
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