Need any tips on tuning a Cothran Powerhouse valve -

I have run the valve up to over 150fpe on my arrowgun and over 100fpe on the 9mm carbine. It is capable of much more. If memory serves it will support 270fpe. The only tuning tips I can give are to match your transfer ports, don't over do it on the hammer spring and let the valve do the rest.

Not sure but a 22xx hammer spring may be a bit light on a pcp gun try it to be sure. I am using the spring from a Discovery on the arrowgun at 2K+psi.

Man, Steve, the way you have your tools oriented, I was eyeing that red colored AR style soldering iron that comes with its own black handle and chrome shoulder rest, till I finally figured out what was going on, lol.

Not sure but a 22xx hammer spring may be a bit light on a pcp gun try it to be sure. I am using the spring from a Discovery on the arrowgun at 2K+psi.

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I had read somewhere that the valve worked better with a light hammer spring, so that's where I started. Right now, it seams pretty docile untill the pa reaches a certain point, and then BOOM -

I'm talking really loud with lots of muzzle flip - maybe a stiffer spring would achieve more "linear" results? Will try different hammer springs and see -



Thank you for your comments -

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You are correct but to get to 100fpe with 2kpsi I had to use a heavier spring for the 9mm. Lighter spring is always better only go heavier if you need to.

It is easy to build power with the Cothran, efficiency can be elusive.....

It is important to have just enough hammer strike (combination of hammer weight, spring, preload, and travel,) as you need to get the valve to open consistently and produce your desired FPE. Run some form of hammer free-flight device be it an SSG, SSS, etc to help with hammer bounce. You want no preload of the hammer against the stem.

When you are at a place where you have close to your desired FPE, reduce hammer strike to the point where you experience extreme reduction in velocity. If you can't achieve this you need to change hammer weight, spring rate, travel, etc so that you can find this area where minor adjustments can have significant change in FPS. Almost like finding where the valve is either on or off..... once here, you want to dial in just enough hammer strike to get the valve to open and achieve your desired FPE. 

The Cothran poppet seal is relatively soft and will collapse a bit after sitting a while, thus requiring a little more hammer strike to open for the first shot after sitting. This is not to be confused with oring stiction, which can also occur if the balance chamber isn't lubed...once you think you have your tune dialed in, Let it rest a while to make sure you have enough hammer strike to not experience a slow shot for your first shot . If you do experience this, dial in a slight bit of additional hammer strike.

Once you have your desired FPE, and hammer strike adjusted as described above you have a Cothran building power and doing it in a much less wasteful manner.

When buying a Cothran, ensure you buy the correct one for your application--- they do not like to run efficiently with down-stream restrictions. In other words, don't buy the .250 transfer port version unless you have at least a .25 with full bore porting.....for most .25 and under applications the .187 is more than sufficient.

Cothrans are great valves, especially when in the right application and hammer strike dialed in properly. I have several in both regulated and unregulated applications ranging from 90 to-a little over 300fpe. I invested/wasted a bunch of lead/nitrogen learning how to use them....I'm sure there are ways to improve upon my methods and welcome any constructive feedback...

You're welcome. IMO, the Cothran is likely a little overkill for a .22 pellet shooter......

Pressure is directly related to velocity/fpe with the Cothran. In unregulated applications, as you shoot and pressure drops after each shot, so will velocity. You will be hard pressed to get the valve to behave in any other manner. This may ultimately require you to start with a relatively low fill pressure. 

For lower powered, sub 70ish FPE Cothrans work best regulated where you control power output with the regulator setpoint.

Don didn't name it the Power House Valve for no reason, lol. They build power at relative ease. Virtually nowhere else on your 7/8 tube gun can you spend $150 and can be virtually guaranteed such a large power increase.