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Old 12-01-2017, 12:04 PM   #1 (permalink)
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Tippmann Tinkering...the Saga Continues

By the end of the night I ended up with this:

20171130_205735.jpg

I figure I should ask for help before I hurt myself.

TLDR: How do I fix shootdown on my 98?

The History

As I recently mentioned in a different post, in April I tested my 98 which at the time had the following modifications:

- HPA (850-900 PSI tank reg output)
- PMI Pure Energy regulator (screwed into the ASA and attached to remote line)
- Deadlywind RVA
- Mainspring kit (brand unknown)

And at that time I ended up with the combination of strongest main spring, RVA about half way in, and input pressure of about 625 PSI to achieve 280 FPS.

I have since installed a DIY lightened hammer and light valve spring (write up on the hammer and results will be posted in the Tippmann section next time I take it apart...keep on forgetting to take pic of the hammer)

The Problem

With the addition of the lightened hammer and valve spring I have been able to drop operating pressure to about 550 PSI, drop from the strongest spring to the second-from-lightest, and left RVA in same position, while maintaining ~280 FPS velocity.

However, I just noticed that I am experiencing shootdown. After reviewing velocity readings from testing in April I don't think this is related to the lightened hammer / valve spring.

When I tested in April I used 3 shot groups to test velocities at a particular spring/RVA/reg combination and observed consistent first-shot velocities being higher than second and third.

However, previously I didn't have a gauge post-secondary regulator, so I couldn't observe the recharge rate of my marker.

What I observed over the last few days was that when I fire, pressure drops about 50 PSI to 500 PSI and it is taking several seconds for my secondary reg to recharge to 550 PSI.

Firing in quick succession shows pressure drop from 550 PSI to 500 PSI on first shot, then again to approx 475 PSI for successive shots.

The Troubleshooting

I started troubleshooting at the tank reg. In April I observed that when tank pressure dropped output pressure dropped too. At 1000 PSI tank pressure the output pressure got as low as 550 PSI, which caused velocity to drop towards the end of my testing.

While that is troubling and abnormal (right?) I filled that tank and retested, then tested with a different HPA tank and observed the same shootdown under both conditions. I don't think this is the culprit.

The next place I looked was the secondary reg which. I haven't ruled this out as a problem, but I did disassemble the top of the reg and clean / oil / examine o rings. It was dirtier than I expected but o rings looked fine. After reassembly the problem persisted.

Finally I decided to add an Expansion Chamber between reg and valve (hey why not...) and still, same behavior.

The Question

so what do I do about shootdown?

Increase pressure is an option I suppose.

What about a LP Chamber? Should I need one to operate at 550 PSI? Seems like I shouldn't at that pressure.
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Old 12-01-2017, 12:23 PM   #2 (permalink)
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Do you have a different secondary reg? Those PMI regs never were very good and I strongly suspect that's the issue. Only other cause of a slow recharge is an extreme obstruction in the air path. If you don't have an extra regulator handy I'd try running with out it for now. Just run the tank direct and lower the main spring tension to get the needed velocity. I find that a softer main spring really helps improve the feel of the shot on a tippmann regardless of operating pressure.

And you're missing the #1 most important modification for lowering the pressure on a tippmann. You're using the stock valve. The air flow grooves on the side of the valve only allow so much flow. If you want more velocity at lower pressure you need to open those grooves up.
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Old 12-01-2017, 12:39 PM   #3 (permalink)
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Originally Posted by Fubarius View Post
Do you have a different secondary reg? Those PMI regs never were very good and I strongly suspect that's the issue. Only other cause of a slow recharge is an extreme obstruction in the air path. If you don't have an extra regulator handy I'd try running with out it for now.

I don't have a different reg but I think I need to get one. Mag and I were talking about getting a palmer's female.

Just run the tank direct and lower the main spring tension to get the needed velocity. I find that a softer main spring really helps improve the feel of the shot on a tippmann regardless of operating pressure.

I could run the tank direct, however I can't go down much on mainspring with the lightened hammer. I am using the second lightest mainspring right now. And I agree that the lighter spring made a big difference. I've wondered if altering the geometry of the end of the sear would help too (rounding it perhaps).

And you're missing the #1 most important modification for lowering the pressure on a tippmann. You're using the stock valve. The air flow grooves on the side of the valve only allow so much flow. If you want more velocity at lower pressure you need to open those grooves up.

Believe me brother that's on the list! I've been making iterative changes to the setup on my 98 over time and testing to see how the changes affect behavior. Widening the flutes on the valve is the next step.
In Italics bold lol.
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Old 12-01-2017, 12:51 PM   #4 (permalink)
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I know this is an odd question but have you tried using CO2 instead of hpa? I've got a similar 98 Custom that in warmer weather (65 degrees or above) runs at 425 psi and a chrono speed of 260 +/- 5. I'm running a Palmers female Stabilizer into a CO2 expansion chamber in place of the front grip. This also uses a lpk expansion chamber and valve with the slots in the valve massaged a little. I used a rva

as an easy way to change the main spring if needed without breaking the marker all the way down. I'm running the stock/unmodified lpk hammer And i use one spring up from the lightest mainspring. All velocity adjustments are made by the reg. I'm not saying not to use hpa but to try CO2.
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Old 12-01-2017, 12:55 PM   #5 (permalink)
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Here's what I'm running on my A5. I was specifically aiming for the lowest main spring tension possible, lower operating pressure was secondary.



Metal powertube with no choke velocity adjuster. A stock powertube can be modded for this cheaply and easily, but I had it laying around so I threw it in.

Modified stock valve with the grooves widened as much as possible. Heck, they're no longer grooves, they're two huge flat areas on the side of the valve. Opened the back notches found on an A5 valve a little as well.

Lightened main spring. About 75% of stock (literally clipped off about a quarter of it).

Stock hammer. Lighter hammers need more main spring to get the same valve dwell, and that's opposite of my goal.

RVA, backed all the way out.

Lightest main spring.

A small volumizer on the tombstone. It's a Lapco dual adapter with the inside drilled out. Mostly there to add a gauge and fill in the empty space between the magwell and frame, but adds about a cubic inch of valve volume.

And a Palmer's Female Stabilizer. Currently running at a bit below 500 psi for 290 fps (give or take a little), with the lightest mainspring and RVA backed all the way out. If I up the mainspring tension a bit I could go lower, but I like the way it feels now.
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Old 12-01-2017, 01:04 PM   #6 (permalink)
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Quote:
Originally Posted by JudgeMental1 View Post
I know this is an odd question but have you tried using CO2 instead of hpa? I've got a similar 98 Custom that in warmer weather (65 degrees or above) runs at 425 psi and a chrono speed of 260 +/- 5. I'm running a Palmers female Stabilizer into a CO2 expansion chamber in place of the front grip. This also uses a lpk expansion chamber and valve with the slots in the valve massaged a little. I used a rva

as an easy way to change the main spring if needed without breaking the marker all the way down. I'm running the stock/unmodified lpk hammer And i use one spring up from the lightest mainspring. All velocity adjustments are made by the reg. I'm not saying not to use hpa but to try CO2.
I have tried CO2 but not recently. I am not opposed to using it.

Your springing and pressure sounds to be pretty close to mine...maybe accounted for by your wider valve slots.

That gives me a few more debug steps...CO2 and changing reg.

What about adding a low pressure chamber below my valve? Might that help recharge rate in the valve itself?
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Old 12-01-2017, 01:07 PM   #7 (permalink)
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The solution is to not run a marker designed for high pressure on low pressure

First let me preface this by saying yes, you probably can fix this

But, I hope you are prepared to always have some issues with this marker, when forcing it to operate outside of it's design you will totally have issues and I think that is what you are running into. Like mentioned above your inline reg seems to be a bottle neck but. I would not be surprised to find that out is not the only thing causing shoot down either

Think about this, in stock trim that marker has around 800psi ready to go in front of the valve when the valve opens, there is not a lot of volume there, you have the small space in the valve and the line leading into the marker. Now you have decreased that pressure to 500 but have not given it any additional volume.

If you want to keep running out this way I would do 2 things, rebuild that regulator that you have or simply replace it and add a volumizer. You can also use a expansion chamber for the same purpose but the volumizer or x chamber must screw directly into the valve to serve this purpose.

Personally I would also go back to the heavy hammer, keeps the valve open longer

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Old 12-01-2017, 01:14 PM   #8 (permalink)
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Quote:
Originally Posted by apamburn View Post
What about adding a low pressure chamber below my valve? Might that help recharge rate in the valve itself?
Maybe from shot to shot, but not if it's a hugely noticeable lack of recharge.

Metaphorical example....

You got a water hose, a barrel, and a bucket.

The hose is filling the barrel with water, you are scooping water out of the barrel with the bucket. If you scoop the water out of the barrel faster than the hose is filling it, after a few scoops the barrel is empty and you have to wait for it to fill before you can scoop again.

Now you get annoyed with that, so you get a bigger barrel. But, you're still scooping it out faster than it's pouring in, so while you get more scoops before it causes a problem, eventually you out run the hose and you have an empty barrel again.

The solution isn't a bigger barrel, it's a faster flowing hose, or a smaller bucket.

The hose in this example is your regulator. The barrel is your valve chamber (and a bigger barrel is your valve chamber with volumizer), and the bucket is the air used with each shot.
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Old 12-01-2017, 01:14 PM   #9 (permalink)
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Quote:
Originally Posted by Fubarius View Post
Here's what I'm running on my A5. I was specifically aiming for the lowest main spring tension possible, lower operating pressure was secondary.

https://fubarius.com/pictures/magfed/mk5-1.jpg

Metal powertube with no choke velocity adjuster. A stock powertube can be modded for this cheaply and easily, but I had it laying around so I threw it in.

What is a no choke velocity adjuster? I have mine backed out all the way - looking down tube I can see that it is not inside the valve at all, just screwed into the body.

Modified stock valve with the grooves widened as much as possible. Heck, they're no longer grooves, they're two huge flat areas on the side of the valve. Opened the back notches found on an A5 valve a little as well.

the hammer was hard to cut. Had to sharpen the drill bit twice. Is the valve as hard? Can I take a file to it?

Lightened main spring. About 75% of stock (literally clipped off about a quarter of it).

Stock hammer. Lighter hammers need more main spring to get the same valve dwell, and that's opposite of my goal.

RVA, backed all the way out.

Lightest main spring.

A small volumizer on the tombstone. It's a Lapco dual adapter with the inside drilled out. Mostly there to add a gauge and fill in the empty space between the magwell and frame, but adds about a cubic inch of valve volume.

Where can I get one of these?

And a Palmer's Female Stabilizer. Currently running at a bit below 500 psi for 290 fps (give or take a little), with the lightest mainspring and RVA backed all the way out. If I up the mainspring tension a bit I could go lower, but I like the way it feels now.
Awesome.

RE the hammer, I didn't find your statement to be true. I cut mine by 10 ounces grams (admittedly not much - about 7%) and was able to drop 3 spring strengths and 50-75 PSI.

Based on the results of lightening my hammer, the Tippmann hammer has more than enough mass to open the valve with the stock spring, which makes sense given the 'reliability-first' design of Tippmann - engineers likely wanted the hammer to have enough momentum to open the valve even if there was dirt / paint in the body, weakened main spring, etc...

And when you consider that the hammer was over-engineered to have sufficient momentum in an un-polished body, with regular strength valve spring, and 800-900 PSI input pressure, and that in my (and your) system, all of those have been altered, decreasing resistance (and therefore required force / momentum to open the valve), it follows that the hammer could stand to lose a few ounces.

All that being said, clearly you have figured out a system that works VERY well and if I were in your shoes I probably wouldn't toy with it.

Last edited by apamburn; 12-01-2017 at 01:18 PM.
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Old 12-01-2017, 01:25 PM   #10 (permalink)
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Quote:
Originally Posted by Trbo323 View Post
The solution is to not run a marker designed for high pressure on low pressure

First let me preface this by saying yes, you probably can fix this

But, I hope you are prepared to always have some issues with this marker, when forcing it to operate outside of it's design you will totally have issues and I think that is what you are running into. Like mentioned above your inline reg seems to be a bottle neck but. I would not be surprised to find that out is not the only thing causing shoot down either

Think about this, in stock trim that marker has around 800psi ready to go in front of the valve when the valve opens, there is not a lot of volume there, you have the small space in the valve and the line leading into the marker. Now you have decreased that pressure to 500 but have not given it any additional volume.

If you want to keep running out this way I would do 2 things, rebuild that regulator that you have or simply replace it and add a volumizer. You can also use a expansion chamber for the same purpose but the volumizer or x chamber must screw directly into the valve to serve this purpose.

Personally I would also go back to the heavy hammer, keeps the valve open longer

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Thanks for the warning but not necessary. Half of the fun is tinkering with these and I've read plenty of "it's not worth it" and "don't bother" posts at PBN.

There are plenty - plenty - of people that have taken Tippmann markers down to 500 PSI or less and had them cycling just fine.

I rebuilt the reg maybe 6 months ago and took apart the top of the reg last night; o rings looked ok. But you're right - visual inspection isn't always sufficient and I could stand to rebuild it again.

I'm particularly interested in adding a volumizer to this system to see how it affects output. Any you recommend?

So far I see next steps as:

1. rebuild reg
2. add volumizer
3. open valve flutes
4. replace reg
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