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DCHAP-3

cheap homemade air powered check valve

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#1 CaptainSlug

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Posted 24 June 2016 - 08:23 PM

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I found this link: http://www.sscentral...eck_valves.html

 

The stem valves used in that article can be bought in bulk lots on eBay, and you end up only paying $0.30 to $0.50 each.

If you marry it with a cut-to-length spring and add the required pipe fittings you end up with a check valve that costs $2.

eBay - 1-1/2" Tire Stem Valve (TR414)	$4.14 for 10 ($0.41 each)
9663K85	302 Stainless Steel Cut-to-Length Compression Spring, 20" Length, .750" OD, .062" Wire Diameter = $5.42 (Cut a 2-inch section for $0.54)
4880K432  SCH40 White PVC Pipe Fitting, 3/4 Socket Female x 1/2 NPT Male, Reducing Adapter	$0.55 each x 2 = $1.10
2-inch long section of 3/4 SCH40 pipe = $?.??

The check valve design is great, but the only draw-back is that it looks like it would have a restrictive output. That issue inspired this, which is an updated version of DCHAP-1 with a scratch-built pump and a more normal grip and trigger.

DCHAP-3_000.jpg

DCHAP-3_001.jpg

 

The pump is inside-out. You move the outer tube over the plunger head and check valve in order to pump it. To accomplish this the M-F adapters and NPT coupler have to have their faceted sections sanded off.

 

I need to build and test the pump first. I'm not currently sure that the o-ring-based check valve on the plunger head will work. If it doesn't then I'll just stick another $2 check valve onto the end of the pump handle. The alternate course to take would be a ball pump.

 

Another item in the cards for this project is that I would like to make an adjustable over-pressure valve using the same parts.

 

Here's the part list for the above diagram.

http://www.captainsl...rf/DCHAP-3.xlsx


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#2 Langley

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Posted 24 June 2016 - 08:47 PM

 If it doesn't then I'll just stick another $2 check valve onto the end of the pump handle. The alternate course to take would be a ball pump.

 

Another item in the cards for this project is that I would like to make an adjustable over-pressure valve using the same parts.

 

I think you could probably get away with a simple flap gate on the pump handle, using a piece of inner tube rubber and some holes drilled in the end-cap.  It wouldn't have to be perfectly air tight to work. 

 

Looks great, looking forward to seeing the OPRV.


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#3 Snoop Doggy doge

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Posted 24 June 2016 - 09:05 PM

Water warz is leaking over into nerf?
Ya'll gonna go to waterwar.net and stuff soon? 

Also, does this mean we're going to gradually accept homemade air tanks, as long as they have OPRVs?
I think that'd be great


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#4 CaptainSlug

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Posted 24 June 2016 - 10:02 PM

An OverPressure Valve is nothing more than a check valve with a cracking pressure that's set by the spring load. In this design the area of the seal exposed to the pressure that you are attempting to vent is 0.304 square inches. So that means that if you want the check valve to open and leak at 10 psi you need 3.04 pounds of spring load from the spring. If the pressure goes above 10 psi the check valve will open the OPRV and vent the excess to atmosphere.

 

hoprv.jpg

You can adjust the relief pressure upwards by tightening the thumbscrew, which compresses the spring further. Loosening the screw lowers the pressure set-point. With a gauge added to your pressure vessel you can tweak your pressure ceiling whenever you want.

 

Pressure regulators work in a similar fashion, but with the adjustable spring load pushing against a diaphragm that's actuating a poppet.


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#5 Langley

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Posted 24 June 2016 - 11:06 PM

Edit: Yeah, I guess it's just a conveniently shaped stopper. I don't follow why you are using the tire stem valve in this configuration.  Is it just a conveniently shaped stopper? Why would air  need to flow through it?
 
My major concern with any homemade airguns is that they are easy to make totally overpowered.  This design looks great for testing, but there's nothing to stop someone from cranking up that thumbscrew until the spring is fully compressed.  $15 blasters with mostly off-the-shelf parts is a noble cause, but I don't know how I would make them fair to use at a war without a chronograph and maybe some security screws.
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#6 Meaker VI

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Posted 24 June 2016 - 11:58 PM

My major concern with any homemade airguns is that they are easy to make totally overpowered.  This design looks great for testing, but there's nothing to stop someone from cranking up that thumbscrew until the spring is fully compressed.  $15 blasters with mostly off-the-shelf parts is a noble cause, but I don't know how I would make them fair to use at a war without a chronograph and maybe some security screws.


And we keep getting flack from safety-minded air builders for allowing PVC tanks and fittings at all (from a conversation with Doom and torukmakto4 on Reddit the other week). They'd prefer all-metal rated fittings, and I can't fault that. It's just super expensive to do.
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#7 CaptainSlug

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Posted 25 June 2016 - 07:24 AM

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I don't know how I would make them fair to use at a war without a chronograph and maybe some security screws.

 

I'm really only doing this to tinker, though I would like to make something that can shoot foam balls and absurd-size stefans a good distance and the first DCHAP did that really well. It's only downside was how cumbersome it was. If people find legitimate uses for these parts then that's the whole point. Homemade Air guns have never been popular at wars.

 

My favorite primary of all-time was the BuzzBee Big Blast and If I can find a way to make one of those from scratch I would be tickled pink.

 

They'd prefer all-metal rated fittings, and I can't fault that. It's just super expensive to do.

And heavy.


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#8 Snoop Doggy doge

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Posted 25 June 2016 - 12:31 PM

My major concern with any homemade airguns is that they are easy to make totally overpowered.  This design looks great for testing, but there's nothing to stop someone from cranking up that thumbscrew until the spring is fully compressed.  $15 blasters with mostly off-the-shelf parts is a noble cause, but I don't know how I would make them fair to use at a war without a chronograph and maybe some security screws.

 

The way to deal with this is Chronograph and spot checks. Spot checks are in between rounds whenever, you check a persons blaster and see what it's chronoing at to make sure someone didn't over clock there blaster. 

I like the design and I think it'd be cool to be able to incorporate and bring in homemade air blasters, but up to 4B power. 


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#9 CCBall

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Posted 25 June 2016 - 01:52 PM

1: Cool blaster!

2: Have you made one yet?

3: Any news on the Abp5k?


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#10 CaptainSlug

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Posted 25 June 2016 - 02:15 PM

1: Cool blaster!

2: Have you made one yet?

3: Any news on the Abp5k?

1. Will be. Waiting for some parts to show up.

2. I've made several DCHAP-1s and only one working DCHAP-2. I'll be making a DCHAP-3 this month.

3. the suitcase it was lost on a bus enroute to a Nerf war in Toronto back in 2010. I have no interest in making something that complicated again.


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#11 Ice Nine

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Posted 28 June 2016 - 01:23 PM

Great design, Slug. I'm looking forward to seeing it built. The only use problem I could imagine was the pump tube being pulled off during vigorous pumping; any thoughts on putting in some kind of stop? Even something dumb like a string stop on the exterior might help.

 

My favorite primary of all-time was the BuzzBee Big Blast and If I can find a way to make one of those from scratch I would be tickled pink.

 

Same here. I tried to do that with the QEV blaster I made but it was more expensive than I would have liked and I couldn't get the blaster feel quite as nice.


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#12 CaptainSlug

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Posted 28 June 2016 - 02:20 PM

Any thoughts on putting in some kind of stop? Even something dumb like a string stop on the exterior might help.

That's exactly what I had in mind because it's cheap and simple.


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#13 DX-Robert

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Posted 28 June 2016 - 02:29 PM

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And we keep getting flack from safety-minded air builders for allowing PVC tanks and fittings at all (from a conversation with Doom and torukmakto4 on Reddit the other week). They'd prefer all-metal rated fittings, and I can't fault that. It's just super expensive to do.


As a long-time PVC and air blaster tinkerer, I agree with them, all or mostly metal.  Well, at least for designs intended to be built by the masses.  People are weird and find all manner of ways to screw things up.  They can't be trusted even with a fully step to step guide.  Rated and even some types of unrated PVC are quite safe, but only if the user knows what they are doing and understands things like the impact of temperature upon the material.

The problem in wars to me isn't the technology, it's the user.  You need a mature, experienced air blaster user who understands the relationship between power and pumps.  As you increase the power and approach a certain threshold, you must flatline the number of pumps or decrease them, else, adding more power makes the blaster *less* effective.  Above that threshold, more range and velocity gives you literally no advantage, while the increased pump count saddles you with disadvantages.  It's the kind of situation where you'd trade 30ft of range for 1 less pump in a heartbeat.  This is the kind of master user that I trust with homemade air in a war (the same goes for HPA).  They know what they are doing with their construction methods, the pressure they are running, the band of values it will chrono at, etc.  Ultimately, homemade air is about creativity and durability, not about power.  The discontinued and breakage-prone 4B is not a long term viable platform vs homemades built to last.

I've found that air homemades are unpopular for several reasons, mostly involving blanket bans out of fear, and lack of understanding about how they work.  You'd be surprised at how many people look at air and think magic, yet they are far simpler and easier to construct than springers.

My QEV arrived today, so it's time to start moving on that.  Price is definitely a barrier to entry, but this valve was $22 and American-sourced, NPT, which is pretty decent.  These things are probably not going to feel as nice as a 4B or anything with an injection-molded shell, but there's room to explore.
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#14 CaptainSlug

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Posted 01 July 2016 - 09:51 AM

I have two check valves and the trigger valve put together already. I need to run back to home depot to pick up a few parts for the OPRV, then I can start machining the frame parts and grip.

DCHAP-3_002.jpg

These 1-1/4 to 1/2 bushing adapters are very sloped on the inside which is nice because it helps keep all the parts in alignment. The trigger valve seat is the end of the 1/2 SCH40 stub.

 

Update: Pump doesn't work worth a shit. Not sure why. First check valve might have a cracking pressure that's too high. Will run some more tests over the weekend.


Edited by CaptainSlug, 01 July 2016 - 07:50 PM.

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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

#15 Cartaya

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Posted 03 July 2016 - 12:42 AM

I have been looking this over for the last few days and I was wondering about the 1/4th rod that goes inside the 1/2 inch elbow to the valve stem that discharges the air in the reservoir.   Is that just a 1/4th" hole? no o ring? would that be a big deal? or would any air loss be negligible to the point it doesn't matter with an air dump that size?


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#16 CaptainSlug

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Posted 03 July 2016 - 08:18 AM

I have been looking this over for the last few days and I was wondering about the 1/4th rod that goes inside the 1/2 inch elbow to the valve stem that discharges the air in the reservoir.   Is that just a 1/4th" hole? no o ring? would that be a big deal? or would any air loss be negligible to the point it doesn't matter with an air dump that size?

The loss is on the output and the flowrate of the output from the trigger valve tends to be so high that any minor loss through the gap around the rod and elbow hole won't impact performance. DCHAP-1 was capable of shooting beyond 200 feet at only 15 psi. 5 psi could manage 120 feet easily.

 

What I need to figure out here is the OPRV, which will allow me to dial in a maximum pressure level so I can keep this safe to use.


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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

#17 Cartaya

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Posted 04 July 2016 - 03:14 PM

I'm thinking this has to be doable in PVC and much smaller, a wastegate set to whatever pounds you want.

Also, to help get the right spring weight for the gate seal, this spring calculator helps, you have to know length, wire gauge, diameter, active coils (the ones that are pitched, not flat), at the end of the results there is a place where you can select an exact compression height and get the yield at height.

On my way to Redondo Beach yesterday for the 4th, I was toying with an idea in my head to use 1/2 NPT and a thread cap (twist the cap to set the pounds), drill a hole, put in a small tub cap in as a seal and a small Home depot spring behind it.  Like the tiny tiny one that comes with the Everbilt Home Depot 4"x7/8thsx.080 spring nobody ever has a use for.  I forget the dimensions of that spring, might be too heavy anyawys, but I think the right 1x1/2x maybe .072 gauge spring should do the trick.





 


Edited by Cartaya, 04 July 2016 - 03:20 PM.

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#18 Daniel Beaver

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Posted 04 July 2016 - 06:03 PM

Water warz is leaking over into nerf?
Ya'll gonna go to waterwar.net and stuff soon? 

Is that site more active than Super Soaker Central?


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#19 Snoop Doggy doge

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Posted 04 July 2016 - 11:04 PM

Is that site more active than Super Soaker Central?

 

Yea, SSC is an archive, the people moved to WWN


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