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Stronger Opv Spring?


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#1 cheesypiza001

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Posted 03 March 2009 - 06:17 PM

I have had 3 AT2Ks so far, 2 of which have been been damaged by over-pumping. I always either forget that I already pumped it, and pump it another 2 times before I realize that I pumped it too many times. Anyway, I realize that plugging a pump can greatly increase dart velocity. However, with this advantage comes potential consequences. I always wondered if replacing the over-pressure-valve spring with a spring of greater strength, would enable one to achieve the dart velocity of a pump-plugged blaster, yet maintain the OPV for blaster safety (making sure the air tank doesn't explode).

I do plan to try this. However, if someone who has previously attempted this, or someone with good reason to support their thoughts says that it will not work, then I will not attempt this. Please do not think of this as the chronic concept thread that does not end up following through.

Edited by cheesypiza001, 03 March 2009 - 07:22 PM.

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#2 death by cheez

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Posted 03 March 2009 - 06:19 PM

Have fun with getting the tank open, replacing the spring, and getting it back together while having it keep the same pressure and have no leaks.
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#3 Draconis

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Posted 03 March 2009 - 06:19 PM

This is one reason that I install pressure gauges on all of my pump plugged blasters. Well worth the $5 for a tire pressure gauge.
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#4 Ice Nine

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Posted 03 March 2009 - 06:29 PM

Have fun with getting the tank open, replacing the spring, and getting it back together while having it keep the same pressure and have no leaks.


The overpressure release valve is not in the tank. It is almost always at the back of the pump (on the head), except in some cases where it is on a bladder plug or trigger mechanism, such as the Magstrike or SMDTG respectively.

I seem to recall Just Some Bob doing an OPRV dissection thread, it's probably well worth checking out. That said, I don't think I've seen anyone replace the spring.
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#5 TantumBull

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Posted 03 March 2009 - 06:29 PM

Woah woah, woah, wait a sec. Where are you getting pressure gauges for 5 bucks a piece?
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#6 Shrub

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Posted 03 March 2009 - 06:34 PM

I've seen em' for a buck at Lowes.
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#7 cheesypiza001

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Posted 03 March 2009 - 06:50 PM

I seem to recall Just Some Bob doing an OPRV dissection thread, it's probably well worth checking out. That said, I don't think I've seen anyone replace the spring.


After looking at that thread just now, I found this:

Nice JSB, I really like the "health video" feel. So I'm gussing the OP valve works on the BBBB by that spring being pushed back when the pressure is enough to compress the spring. Then it closes again when the pressure is weak enough to not be able to keep the spring compressed. Hmm, so maybe by replacing that spring, one could essentially allow the gun to work at higher pressures, but still leak air when it is pumped enough to blow the tank. The real trouble would be doing the math to find out exactly how strong a spring you would need in order for it to leak air at a specific PSI.


I did search prior to posting, but I guess I missed this.

Also, can anybody give me some suggestions on (as Tantumbull said) "the math to find out exactly how strong a spring you would need in order for it to leak air at a specific PSI"?
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#8 cheesypiza001

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Posted 03 March 2009 - 07:21 PM

Also, can anybody give me some suggestions on (as Tantumbull said) "the math to find out exactly how strong a spring you would need in order for it to leak air at a specific PSI"?


I've just done trial & error.

Also, the AT2K should be a really cool choice to start playing with OPRVs - first drive out the metal pin holding the pump head onto the shaft, then carefully drill out the bottom of the OPRV - by hand so you don't ruin the spring - and then you can make a different length pin to shim up the spring, or insert another spring, a different spring ... anything you like. You can insert parts, and pin it back to the pump shaft - test as many combinations as you like - without the need to glue anything in place.

(note: I've studied it and am confident that should work, but have not in fact actually done all that to an AT2K pump just yet)


Couldn't I theoretically calculate the PSI at which the stock OPRV goes off at, then measure the push force of the spring used in the OPRV, next, establish a ratio of pumps to spring force, and lastly, compare the ratio to the PSI in the air chamber when the pump is plugged? It would go something like this:

Posted Image
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#9 cheesypiza001

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Posted 03 March 2009 - 11:50 PM

Also, the AT2K should be a really cool choice to start playing with OPRVs - first drive out the metal pin holding the pump head onto the shaft, then carefully drill out the bottom of the OPRV - by hand so you don't ruin the spring - and then you can make a different length pin to shim up the spring, or insert another spring, a different spring ... anything you like. You can insert parts, and pin it back to the pump shaft - test as many combinations as you like - without the need to glue anything in place.

(note: I've studied it and am confident that should work, but have not in fact actually done all that to an AT2K pump just yet)


I just followed your instructions. However, I cut the plunger head in half in order to open it up as opposed to drilling from the bottom. Here is a picture:

Posted Image

The springs at the bottom are an assortment of spring that are similar to the stock OPRV spring. I'm pretty sure the stock spring is on the top and the one I replaced it with is right below the stock one, though I may be wrong.

I then took out another piece of plastic that was in between the upper and lower half of the plunger head.

Lastly, I gooped the sides up and clamped it together. Some more pics:

Posted Image

Posted Image
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#10 Zorns Lemma

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Posted 04 March 2009 - 12:31 AM

Pressure = Force/Area

Assuming you keep the configuration of the OPRV (Area) the same, doubling the force of the spring will double the maximum pressure that the pump can achieve against the fluid from the other side of the check valve.
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#11 cheesypiza001

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Posted 04 March 2009 - 12:37 AM

Pressure = Force/Area

Assuming you keep the configuration of the OPRV (Area) the same, doubling the force of the spring will double the maximum pressure that the pump can achieve against the fluid from the other side of the check valve.


Yes. In fact, the spring I added was just about twice the strength of the stock one.
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#12 Draconis

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Posted 04 March 2009 - 02:08 AM

Woah woah, woah, wait a sec. Where are you getting pressure gauges for 5 bucks a piece?


Carquest. But there are lots of similar designs of cheap tire pressure gauges that are at various stores. I'm sure there is a similar design at Harbor Freight, Sears, Lowe's, Autozone, etc.
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#13 Split

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Posted 04 March 2009 - 02:55 PM

I've stuck with Mcmaster OPVs. Bob says that they're expensive, but for what, $10 (including the T and coupler) + shipping each you can get a big brass thing tuned to exactly where you want it, with a pin pull to release the pressure in the system at will. Just an option to consider. It's significantly less work, and works on any air blaster.
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#14 Draconis

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Posted 04 March 2009 - 05:18 PM

Here is a six dollar gauge that is eligible for free shipping. I also found a digital one even cheaper.



Oooh... That digital gauge is sexy... I may have to use one when I finally mod my AT4k.
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#15 cheesypiza001

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Posted 04 March 2009 - 05:25 PM

Well, I took the modified OPRV out of the clamp today and it did not break!............yet. :P

Here is the piece:

Posted Image

I will test it in my AT2K that I will be getting in about a week, and update this thread then.
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