Low Pressure Kit Issue?

Okay, so this problem started to manifest itself last season but, I played through it.  Now it's getting to the point to where I need to do something about it.

Basically, I've had my LP kit for some time.  I noticed last season that my output pressure was just barely able to get the ball out the barrel (Freak with 10" Stiff-Tip front) at 280 fps.  This wouldn't be a problem  but, my field limit is 290 and only the peak shots get into the low 280s.

I've got the 'velocity screw' (power tube choke) out so that the screw is flush with the inside of the tube.

I'm using the low pressure fittings for my RT (it works great).

My reg is all the way up to 400psi (and it's rock solid at 400, it doesn't drop for even a milisecond during shooting).

My internals are polished and well lubed.

My barrel was on the looser side of a perfect fit.

Any ideas as to what the problem could be?  Is it possible my main spring is getting too soft?

That's what I suspected, just making sure. Thanks.

I have a spare hammer / mainspring combo around here somewhere, I'm gonna have to see how it compares with a hand squeeze- can;t shoot again until next weekend at the soonest.

I'll update based on

I wouldn't think so, the RT shouldn't be the culprit here, try replacing your banjo fitting with the extra screw and try it, if you still cant get above 280 then the RT isnt the Problem.

How long have you had your 98? Mabye your valve is just starting to go.

Check your airlines with soapy water, mabye you have a leak somewhere.

This is a particularly confusing issue mainly because I went straight from an LP and E-Bolt setup to an LP and R/T setup.

I double-checked all my fittings (post secondary reg) and no leaks. 

I agree with you Tallen that it's a matter of time / airflow.  Time would be determined by the strenght ratios of the main spring and the valve spring.  That's why I replaced the main spring since I thought it had gotten too soft.  I'm gonna give it a thorough cleaning tonight and I'll take the opportunity to double check that the ASA/volumizer is free flowing and that the volumizer isn't full of oil or other debris.

   I've disassembled the valve several times to ensure that I have the right valve body (with wider, deeper flukes), The wider necked pin, the longer valve spring guide/valve endcap, the wider opening cup seal seat, and the softer spring.  The inside of the valve has always been clean when I take it apart (I never use teflon, only loctite which I thoroughly clean between reapplications).

I don't believe it's any blockage downstream of the reg as it recharges like a champ between shots, even with strings of the R/T.

More to come later.

Edit: I will try disabling the R/T with the screw and if it is the R/T I'll try switching to the 1/16th fittings (local pro-shop upgraded me to 1/8 fittings when they heard I ran with the LPK).


Edited by UV Halo - 16 April 2007 at 10:12pm

Black Shadow-
  I suspect that may be the case if I switch to the 1/16ths.  However, if the gun works at the propper pressure range without the R/T, then, I believe it means that too much gas is going to the rear (via the R/T).

My stock isn't attached to the body.  It's a gas through bottom line "T" Stock (I got pics in the gallery here - Minus the E-Bolt now).

Tried running without the R/T and I'm still stuck below 280 at 400psi.  I'm going to try to switch out valve parts with some of the parts that came with my E-Bolt kit.  I'm not getting my hopes up here.

I certainly am and I have verified that the air path is clear.  Everything has had zero effect on velocity.  Generally speaking, valve bodies do not go 'bad'.  The springs get softer, seals get worn or damaged, and valve stems may get badly worn.  I have checked for all of these things and have found nothign to be a contributor to this problem.

Now, a couple things have come to my attention.  I happened, via a google search, to find a Tippmann troubleshooting FAQ (via google) with the question along the lines of 'What if my LPK isn't working'.  Well, mine is working, just not as well as I thought it should.  It turns out that Tippmann recommends that LPK users set their regs to 325-400.  Well, it seems that my particular gun wants to run at about 450 in order to meet 290-300fps.  So, if the airway was clear, the springs are good, and the seals are working, what could be the issue?

I think I realize what it is.  Background:

When I first got my 98, I had an LPK on it.  It worked in the 300s (I'm just remembering this).  Eventually, as some of you may remember, I got an E-bolt and had it working for awhile (in the 200s).  Well, while it was working, I took my LPK valve and gave it a 'valve hush mod' that Bruce described to me.  This was essentially a one-way conversion that disabled my blowback (metal strip JB welded to hold an o-ring over the blowback hole).  Well, then my E-bolt (the ram) died on me so, I went out and picked up another LPK for the valve and an R/T (with the LP fittings).  I've since had this newer valve in and I realize, that it was at this time that I started to have this velocity issue.

The only thing that has changed (other than the R/T which I have switched out) is that I'm using the newer valve.  I haven't checked but, I'd be willing to bet that the newer LPK valve has something different in its geometry.  Maybe the flutes, while bigger than the standard M98 valve, are smaller than the other LPK valve I have, or maybe it has a smaller interior volume.  So, in other words, maybe this valve is just slightly out of specs.

I replaced the valve end cap (I can't remember the name but, it's opposite of the valve stem) with one that came with the E-Bolt.  For those that don't know the difference between the two, the LPK piece has a post that projects into the interior of the valve and serves as a spring guide.  The idea is that by using the E-Bolt piece, I have enlargened the volume of the valve which should help with velocity.  I haven't had a chance to test it out for velocity yet but, it cycled fine with the R/T back on it.  My only concern as that while dry firing on occasion, the valve stem goes far enough into the body to go out of alignment and bind in the open position.  This didn't happen under cycling with pressure or even when using the R/T.  I think the pressure in the valve keeps it from going that far.  I hope to find out this weekend how it shoots.  In any case, I'll be taking the other valve cap and, my Air America "Black Ice" reg which can go higher than the palmer fatty.

Edited by UV Halo - 21 May 2007 at 1:54pm

The screws are definitely holding the valve in place.  You'd think it's not possible but, here are some related notes that may help you understand.

In a review of the LPK somewhere, (maybe model98.org, a long time ago) I read that the purpose of the elongated central post of the LPK "Rear Valve Plug" (I just checked Tippmann parts for what they are calling it) is to keep the spring from binding.

  When I was considering the swap last night, I realized that if you look in the valve, there really is no room for the spring to bind on itself.  The inner chamber is not that much wider.  Something I always noticed (but never thought about) though in dissassembling the LPK valve is that you can't push the Rear Valve Plug as far in as you can the standard valve's- You can't even get the tip of the pen cap clip in there.  I think the real purpose of this post is to keep the valve stem from moving too far into the valve body.  Because, with this rear valve plug in place, the end of the valve pin can only go about 1-2mm deep into the blowback hole, not enough for the tip to move beyond the inner side of the blowback hole.

  If it does, it can shift off-axis and catch inside of the blowback hole (which is what it did only while I was dry firing (with no air, something I always do after re-assembly to make sure parts are moving properly).  What I noticed is that while dry firing, it would click like normal as the bolt hit the valve pin and depressed it to rear face of the valve.  But sometimes, it would have more of a ping than others and when it finally started pinging every time, I decided to open up the shells and see what was up.  Sure enough, the end of the pin was logged on the internal wall of the blowback vent.  The ping was from the bolt hitting the bolt face with no resistance.  It didn't happen when I un-jammed it and then cycled it a bunch with gas (with the R/T, I'm guessing 100 cycles). 

Now, I believe that the reason this is that because of the valve pin/spring and mainspring rear bolt balance.  When that rear bolt hits the valve pin, it imparts it with energy that the pressurized gas, and the valve spring resist.  These two factors slow the pin down and gradually return it to the closed position.  However, with no pressurized air in the valve, it's purely big bolt and mainspring versus little valve stem and little valve spring.  Inside the normal LPK valve, the valve rear plug stops the pin from moving too far in should there not be any pressure in the valve.  With my setup, the valve pin continues forward until the spring finally resets it.  This also jives with why I experienced no FPS gain even after I cut one of the valve springs, the rear plug was keeping it from opening any further.

I'm not sure how this will actually hold up under actual firing conditions but, I've got the LPK rear plug in my tool bag and, the black ice reg (with LP spring pack) ready to go.  I might miss a game or two but, I'll get it working one way or another.  Potential further long term options include widening the flutes on the valve.

Believe me, I'd really love to have my E-Bolt back in my gun but, it's got two obstacles.

1. Sombody was supposed to check the resistance and direction for the diode I'm missing on my board
2. My ram cyclinder and shaft are shafted (I was looking into having a replacement built when I found out my board was damaged while in storage).

I really like the sleeper effect my gun had when e-bolted and I just found a field out here that allows full auto :P

Hehe, It's cool.  My board will be waiting :P

The problem turned out to be the Reg and the gauge.   The reg for being a little too tight to turn at it's top-end and, the gauge for overstating it's output PSI.  The combination of which caused me to think I couldn't get my FPS up.

Today, it shot excellently!  It's now back up to speed.

Next task, finish this dang Ion I've been working on and then, resurrection of the E-Bolt!