12 replies to this topic

[TantumBull]

Damn it feels good to post a new topic. It's certainly been awhile. Okay, story time.

Some of you may remember my homemade adjustable oprv, which if I remember correctly, has since been revised and improved by Venom. I'm not sure how many of you made them, but I know that mine always gave me trouble. It always took forever for the valve to release air from my 4B (which is also due to the high volume of a 4B). After the initial pop, it would literally hiss, sometimes not even audibly, for the next 5 minutes until it reached equilibrium. Intially I thought this was simply a problem with my design. I tried all sorts of things - I added 1/4" o-rings to the valve to create a perfect sealing face for the BB. Didn't work. I mixed and matched springs. Didn't work. I changed out the sheath for the whole assembly. Again, didn't work.

Essentially I just got frustrated with the project altogether, and I tossed it. I figured my valves were just dysfunctional. So I got my handes on a 4B pump head, and gutted it for the OPV valve. That I fitted with a barbed fitting, and hooked it up to the 4B. Same problem. Having modded for several years now and knowing how many more mistakes I make when I'm angry, I set down my tool and went and did something else. And didn't really come back to it. Unitl later...

Several months ago, I was examining a 3k pump assembly for no particular reason. When it hit me... nerf blasters always put their OPRV's in the pump heads. But why do that? Certainly it would be easier from an engineering standpoint to attach them to the actual tanks, where space isn't as much of a constraint. The answers pretty simple: putting the valve BEFORE the check valve leading to the tank solves all the problems I've been encountering. For one, the air in the pump tube isn't constantly under >atmospheric pressure when pumping the blaster. Only in spurts. More importantly, the check valve cuts off the tank from the relief valve, so the tank never leaks! I felt soooo stupid when I realized this, Hasbro had been doing it forever and I just rediscovered the concept.

Recently I got kinda back into nerf, and was getting my primaries ready for the summer wars that I'm going to try to get out to. My 4B, the most reliable thing ever, was in pristine shape, as usual. But holding it made me remember the really scary sound it made when it shot, and how frightened some people got from it, knowing it was plugged (it has a ball pump installed). So I decided to change that. I've found that people will feel much more comfortable around blasters with OPRV's, even if they're shooting harder than other plugged blasters (like 2k's and 1.5k's). So I installed one from a 4B pump head in the manner I described above.

/novel


The valve is position right at the end of the ball pump's stroke in a little gap of deadspace that occurs right before the check valve. I simply drilled a hole and superglued in the tip of the barbed fitting I had put on the valve long ago. No vinyl tubing necessary. The hot glue is there for structural support, NOT for sealing.


When the blaster's all closed up, you can see how the back end of the relief valve is exposed for easy access and adjustments.

VIDEO DEMO OF THE VALVE IN ACTION

One more thing: although I did this on a 4B, the concept is universal. It can be done on any air gun, provided there's enough space between the check valve and the pump, and that the new valve introduces a trivial amount of deadspace.

Edited by TantumBull, 05 July 2011 - 02:07 AM.

[Nate45]

What would be the point of doing it that way to your BBBB? You would still have to use the stock pump so why use the OPRV there when the stock pump already has a OPRV?

[TantumBull]

What would be the point of doing it that way to your BBBB? You would still have to use the stock pump so why use the OPRV there when the stock pump already has a OPRV?

Right, but that's assuming you're gonna use the stock pump. Many, like myself, hate how little air that things puts out. Ball pumps increase your ROF quite a bit. This also has the advantage of being able to adjust the pressure levels - you'd have to cut off the pump handle to access that screw on a stock 4B.

But yes, if you are perfectly satisfied with the stock pump, then obviously there's not much reason to do this. But that's why people mod: to change things they don't like.

Edited by TantumBull, 04 July 2011 - 06:23 PM.

[Nate45]

Oh ok thanks for clearing that up.

[ChaosPropel]

Very excellent, TantumBull! So could you use a homemade OPRV, with the same location/orientation as you did with the 4B pump head?

[Curly]

So having the OPV connected before the tank makes it dump air faster? That's handy to know.

[Zorns Lemma]

One more thing: although I did this on a 4B, the concept is universal. It can be done on any air gun, provided there's enough space between the check valve and the pump.

With the new trend in pump replacements, this is not always feasible. The reason why Hasbro puts the check valve at the end of the pump and the OPRV at the pump head is because these two locations are the closest to the pump head, where pressure buildup is highest. Even a small amount of tubing splicing between the check valve and the pump will greatly increase the difficulty in pumping. This is probably negligible when compared to the already large forces on a ball pump but may be very nontrivial in pump replacement with smaller ID pumps.

The issue with OPRV located away from the pump head is that because pressure buildup is not as fast/high, the valve doesn't open as dramatically and thus flow is reduced. The easiest way to get around this is using valves with high flow and not restricting flow to the valve (like that vinyl tubing + goop shenanigans I see people doing with their 4Bs. That amount of constriction is very nontrivial).

So while this solution probably works great for you, it doesn't solve the larger problem of blasters operated at unsafe pressures. A better solution is to use industrial relief valves ($$$) or to design one with higher flow, probably starting with larger surface area for higher pressure sensitivity.

[TantumBull]

Oh ok thanks for clearing that up.

Sure thing, bra.

Very excellent, TantumBull! So could you use a homemade OPRV, with the same location/orientation as you did with the 4B pump head?

Correct.

So having the OPV connected before the tank makes it dump air faster? That's handy to know.

If it's placement is like mine, yes. Zorn gave a much more detailed explanation.

With the new trend in pump replacements, this is not always feasible. The reason why Hasbro puts the check valve at the end of the pump and the OPRV at the pump head is because these two locations are the closest to the pump head, where pressure buildup is highest. Even a small amount of tubing splicing between the check valve and the pump will greatly increase the difficulty in pumping. This is probably negligible when compared to the already large forces on a ball pump but may be very nontrivial in pump replacement with smaller ID pumps.

The issue with OPRV located away from the pump head is that because pressure buildup is not as fast/high, the valve doesn't open as dramatically and thus flow is reduced. The easiest way to get around this is using valves with high flow and not restricting flow to the valve (like that vinyl tubing + goop shenanigans I see people doing with their 4Bs. That amount of constriction is very nontrivial).

So while this solution probably works great for you, it doesn't solve the larger problem of blasters operated at unsafe pressures. A better solution is to use industrial relief valves ($$) or to design one with higher flow, probably starting with larger surface area for higher pressure sensitivity.

YES! I was really hoping you would post in this thread, what with your extensive work with 4B's and especially OPV's.

And hmm, I totally see what you're getting at here. I actually was going to try to mount the valve in the actual plunger (the pump rod is 1/2" CPVC that I put in after the original metal one got bent from pressurizing the 4B a little too aggressively), but it seemed like it would be more work than it was worth. If I didn't have that little gap of deadspace to use I probably would have had to though, or create some by shortening the pump stroke. But yeah, using a more compact industrial safety valve embedded in the pump head would have been ideal.

As for flow, my valve is constricted by the ID of the barbed fitting I had originally installed, so to about 1/8". Mine functions fine even with such a small valve inlet, but maybe the low flow creating harder pumping comes into play more when significant deadspace is also introduced. Its also entirely possible that I simply can't detect the difference because, as you pointed out, the relative change in pumping difficulty would be very small if indeed present in my set-up.

[Zorns Lemma]

If I didn't have that little gap of deadspace to use I probably would have had to though, or create some by shortening the pump stroke. But yeah, using a more compact industrial safety valve embedded in the pump head would have been ideal.

As for flow, my valve is constricted by the ID of the barbed fitting I had originally installed, so to about 1/8". Mine functions fine even with such a small valve inlet, but maybe the low flow creating harder pumping comes into play more when significant deadspace is also introduced. Its also entirely possible that I simply can't detect the difference because, as you pointed out, the relative change in pumping difficulty would be very small if indeed present in my set-up.

I think this is a brilliant solution to the specific problem you were having. The small ID of the fitting doesn't really matter because you're generating a lot of pressure at the pump (and the larger head of your ball pump means it's much harder to "overpump" and stress out your OPRV; probably one of the reasons you only ever got a trickle since you never hit a ton of overpressure anyways).

But it's unfortunate that this isn't a solution to replace poor construction of OPRVs in bike-pump big blasts that are quite unsafe. My original one had no problems whatsoever and has survived Kane's "try to overpump it as much as possible to explode the tank" examination, but I'm pretty sure that the actual design is not resilient enough to be idiot-proof.

[TantumBull]

But it's unfortunate that this isn't a solution to replace poor construction of OPRVs in bike-pump big blasts that are quite unsafe.

By this you mean people who make OPRV's from scratch and install them?

[TheRedRanger]

So while this solution probably works great for you, it doesn't solve the larger problem of blasters operated at unsafe pressures. A better solution is to use industrial relief valves ($$$) or to design one with higher flow, probably starting with larger surface area for higher pressure sensitivity.

I was slightly put off by this whole "put the oprv before the check valve" idea, as I am working on an airtank design with a homemade oprv connected directly to the pressure chamber. The oprv is made of 1/2" PVC and seals with a 9/16" ball bearing though, so hopefully as you mentioned the flow will be high enough to account for the slower pressure buildup. I'll try and see if I can finish it up tomorrow after work and report my findings.

[TantumBull]

I was slightly put off by this whole "put the oprv before the check valve" idea, as I am working on an airtank design with a homemade oprv connected directly to the pressure chamber. The oprv is made of 1/2" PVC and seals with a 9/16" ball bearing though, so hopefully as you mentioned the flow will be high enough to account for the slower pressure buildup. I'll try and see if I can finish it up tomorrow after work and report my findings.

Awesome! It'll be great to know if the relief valves could be connected directly to the tank and still perform reliably!

[TantumBull]

Found an INCREDIBLY easy way to make the OPRV tamper-safe. Unless the wielder carries a screwdriver during rounds, the screw can't be adjusted.