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Pump Replaced 4b With Stock Oprv

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#1 Zorns Lemma

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Posted 20 January 2010 - 05:43 PM

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http://www.youtube.com/watch?v=rL7YLuhHWsc

Start by drilling a 1/4" hole in your tank (don't worry about random plastic shards that get into your tank, we'll deal with those later).
Then solvent-weld in a section of 1/8" ID, 1/4" OD flexible PVC tubing. I used Oatey's Red ABS/PVC/CPVC cement.
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Next throw a 1/2" to 1" PVC slip bushing on there.
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Minimize your shell if you want. Mine started off minimized already. If you don't minimize your shell then you will have to do some extra steps and cutting to get everything to fit nicely.

Drill two holes in the left side of your shell, a 1/4" one near the top for the tubing to your tank, and a hole in the handle for your pump. The pump I used has an L-shaped head with circular face, so I could drill a 1" hole and be perfectly fine. If you have a pump with a weird face then you will have to get your dremel out and carve out the hole until the pump fits snugly.
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You will also have to cut half-circles in the front handle on both sides of the shell so the pump tube will fit nicely in there.
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Now mount your pump in there. If you made the holes nicely, the shell will take almost all the stress of the pumping motion and you will only need to fill in the gaps to prevent pump wobble. You may also have to cut parts off of your pump so that the shell will close. Depending on the pump you have this might be very easy to do or extremely risky. Shave off small amounts at a time to make sure you don't cut into the pump head and thus introduce a new air path for all the air of your pumping to escape to.
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While we wait for our adhesives to cure, reinforce the trigger.
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I cut out two pieces from 1/8" PVC sheet to reinforce the sides of the trigger and solvent-welded them on. Next I filled in the curved piece of the trigger with some epoxy-putty.
Even at absurd (read: totally banned) pressures when testing in the lab, I have not had this trigger break. Depending on how good you were at machining the reinforcing plastic sheet, you may or may not have to widen the horizontal gap in you shell that the trigger sits in.

Now cut off the OPRV from the stock pump and shave down the head slightly, and shave out 3/4" SCH40 PVC until the two fit inside nicely.
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Grab your solvent-weld and attach the OPRV stub into a stub of 3/4" PVC.
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By this time, the solvent-weld on you tank from the earlier steps should have set and be well on it's way to curing. Cut the pump tube off of your tank. Take a 3/4" spade bit and destroy the check valve in the back of your tank. Also dremel out what remains of the pump tube so that 3/4" PVC will fit nicely inside. Now that you have a gaping hole in the back of your tank, flush it with water from the front to get rid of all those plastic shards and shavings that have made it's way in there.
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Finally, solvent weld the stub of OPRV and 3/4" PVC into the back of your tank.
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#2 Nerf Bros

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Posted 20 January 2010 - 06:23 PM

I love it- now I can replace the extra crappy heads on my 4bs with bike pumps and no one can complain!
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#3 nostyleguy

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Posted 20 January 2010 - 07:03 PM

maybe i missed it, but how did you connect the bike tubing to the flexible pvc from step 1? Did u use the bike's hose? or more of the pvc tubing to connect to the pump?

looks very nice. how many pumps till the oprv kicks in?
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#4 polycarb

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Posted 20 January 2010 - 07:16 PM

How did you disable the check valve in this video?
What is the diameter of the pump you used?
This gun runs at stock pressures, right?
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#5 Zorns Lemma

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Posted 20 January 2010 - 07:24 PM

maybe i missed it, but how did you connect the bike tubing to the flexible pvc from step 1? Did u use the bike's hose? or more of the pvc tubing to connect to the pump?

looks very nice. how many pumps till the oprv kicks in?


Vinyl tubing attached initially with a dab of superglue to hold it and then cemented in with solvent weld. I wasn't specific because pumps vary so detail there isn't going to help much.

OPRV kicks in at the 6th pump to leak air to around 5.5 pumps worth of volume.

How did you disable the check valve in this video?
What is the diameter of the pump you used?
This gun runs at stock pressures, right?


Not telling because then some idiot is going to do it at a war and kill someone.
Slightly less than 1".
Yes.
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#6 rork

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Posted 20 January 2010 - 07:31 PM

I like it, even though I use ball pumps instead of bike pumps. However, both are better than the stock pump, and even though the bike pump takes twice as many pumps as a ball pump to fill the tank, you don't have to swap the gun around. I really like the OPV setup, although I'd be interested in seeing if it's possible to attach it via tubing to the outside of the gun...
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#7 Zorns Lemma

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Posted 20 January 2010 - 07:38 PM

although I'd be interested in seeing if it's possible to attach it via tubing to the outside of the gun...


Drill a hole in an endcap for your tubing, attach the tubing, then attach the OPRV. Then just switch pump and OPRV locations (i.e. weld your pump in and attach the OPRV with tubing).
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#8 HOTH

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Posted 20 January 2010 - 09:22 PM

That's very useful. Great job. I also love the reinforced trigger
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#9 Samzilla

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Posted 21 January 2010 - 12:49 AM

How sturdy is the connection between the bike pump and the 4B shell. It seems to flex in the video.
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#10 Zorns Lemma

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Posted 21 January 2010 - 05:38 PM

How sturdy is the connection between the bike pump and the 4B shell. It seems to flex in the video.


It still wriggles a bit. I would suggest filling in the space in the shell with expanding foam rather than hot glue. However, this blaster has been through 3 wars and yet to have any problems so it doesn't really concern me. There is a piece of plastic sheet placed behind the pump head to help redistribute force along the shell so I have yet to see any stress marks.
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#11 Modded Brain 115

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Posted 23 September 2012 - 12:02 PM

Where did you get your PVC/vinyl tubing?
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Edited by Zorn's Lemma, 23 September 2012 - 12:17 PM.

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