Don Cothran M-Rod Power House Valve

[lloyd-ss]

Bob,
I agree with your comments about the plateau and that in general, a lesser hammer hit is needed.  I am working on a light weight and low force SSG for the next round.  Just getting my feet wet with this valve.  The gun is very loud and I had to wear muffs, so it was impossible to tell if there was hammer bounce. 

The next data will be more organized, but I wanted to show how it can be helpful to bounce around a little and see if limits (high or low) are being reached.  I probably did indeed reach some relative  high and low limits, but very crudely.

Wife also said that with the loudness of the gun, no nighttime testing.  The cats are leaving claw marks in the ceiling, LOL.
Lloyd

P.S.  I also fixed the spreadsheet to clarify the spring and striker settings.

[rsterne]

When you get to the knee of the curve, the report will decrease drastically.... you will probably notice that before the velocity starts to drop to any significant degree.... The bell-curve will start to appear after you notice a decrease in velocity and muzzle blast.... but at the moment, you are interested in establishing the relationship between velocity and hammer strike, which will tell you two things.... The plateau will give you the maximum velocity for a given pressure and bullet welght.... and the knee (where the velocity starts to drop) will give you the point where you start to get a reasonable balance between power and efficiency for that combination of pressure and bullet weight.... at least that is how I establish my tuning parameters, for both regulated and unregulated PCPs.... Here are typical plots of velocity vs. preload (for a given bullet weight)....



Bob

[Sfttailrdr46]

I guess my 20" .30 barrel with the Powerhouse valve and SSG should be good for ~100 FPE with a little work

[Motorhead]

LLoyd,
In terms of ALL the SSG designs that have come to pass these past several months, personally have fooled with quite a few.
Not trying to sell you on it ... but FWIW the original design with a floating SSG cartridge & stop rod out the rear cap damped with an o-ring ( in my testing still works best for LOW ES )

In Bob original thread on the SSG, if you take a look at @ post #76 you will see what ultimately became my hands down best performing SSG configuration in my personal guns.
It is super light in weight, VERY consistent once set ... tho a hassle to change power w/o a disassembly.

Just recapping past R&D that may or may not be of some use.

Scott

[shorty]

Those numbers are just incredible. Excellent work with everything.

I have some of the original traditional single wound hammer springs that I first messed around with. If you want them, shoot me a PM.

Made from 1RK91 (similar to PH-17) and tempered to 380,000 psi.

[rsterne]

Don, IMO 100 FPE in .30 cal should be a cake-walk, even with a 20" barrel, assuming the pressure is over about 2000-2200 psi....

Scott, as I said a long time ago, using an SSG in conjunction with a balanced valve (which is what the Cothran Force Reduction system used in the Powerhouse Valve is) should produce outstanding results.... allowing the easier to open valve to be tuned without problems with hammer bounce.... The light hammers and springs you use on your regulated setups may be very close to what is required for the Powerhouse at much higher pressures and FPE levels.... 

Bob

[Erockrocket]

WoW!!!
 I bet it is loud!
My partner in crime and I have decided to go with .30 for our PowerMrod rig. Gonna order the barrel 1st of next week. Once we get some exterior dimensions, we will order a CF sleeve.
 I like the idea of the J-slot, seems it is helping to get full flow.
This valve could wake up alot of Mrods, it makes BIG power!
Keep up the great work, Lloyd.   We are all watching intently

[Sfttailrdr46]

Waiting on .25 bolt from Crosman and a few other goodies then bolt goes to Lloyd for .30 sleeve. Once the .30 bolt is in house I will begin my build and just so I'm clear be prepared for 20 questions since this will be my first major PCP mod and build

[lloyd-ss]

LLoyd,
In terms of ALL the SSG designs that have come to pass these past several months, personally have fooled with quite a few.
Not trying to sell you on it ... but FWIW the original design with a floating SSG cartridge & stop rod out the rear cap damped with an o-ring ( in my testing still works best for LOW ES )

In Bob original thread on the SSG, if you take a look at @ post #76 you will see what ultimately became my hands down best performing SSG configuration in my personal guns.
It is super light in weight, VERY consistent once set ... tho a hassle to change power w/o a disassembly.

Just recapping past R&D that may or may not be of some use.

Scott

Scott, Is this the correct post #76 for the SSG?
Thanks,
Lloyd

http://www.gatewaytoairguns.org/GTA/index.php?topic=102095.60

[lloyd-ss]

Those numbers are just incredible. Excellent work with everything.

I have some of the original traditional single wound hammer springs that I first messed around with. If you want them, shoot me a PM.

Made from 1RK91 (similar to PH-17) and tempered to 380,000 psi.

Shorty,
Thanks very much for the offer on the springs.  I will see what I can do with what I have on hand first, and then might take you up on your offer.
Lloyd

[Motorhead]

LLoyd,
In terms of ALL the SSG designs that have come to pass these past several months, personally have fooled with quite a few.
Not trying to sell you on it ... but FWIW the original design with a floating SSG cartridge & stop rod out the rear cap damped with an o-ring ( in my testing still works best for LOW ES )

In Bob original thread on the SSG, if you take a look at @ post #76 you will see what ultimately became my hands down best performing SSG configuration in my personal guns.
It is super light in weight, VERY consistent once set ... tho a hassle to change power w/o a disassembly.

Just recapping past R&D that may or may not be of some use.

Scott

Scott, Is this the correct post #76 for the SSG?
Thanks,
Lloyd

http://www.gatewaytoairguns.org/GTA/index.php?topic=102095.60

That was the buffer end ... Screwed up on reference post, see #107: http://www.gatewaytoairguns.org/GTA/index.php?topic=102095.msg962792#msg962792

[lloyd-ss]

Scott, Perfect. That's what I needed.
Thanks,
Lloyd

[Stikman]

Thanks Lloyd and congratulations on the first chrony string of a Cothran PowerHouse Valve installed in a Marauder platform. Bravo!!!

I have hope now that this valve can produce the horse power needed to keep my interest with this platform shooting slugs.


Gene

[lloyd-ss]

I am creeping up on collecting some valid data and tuning this valve.  The SSG that I fabricated is close, but the spring is too stiff.  The hammer is only 44 grams.  The spring is .049 wire x .36 O.D. x 2.91 long x 25 coils.  The initial preload of the spring in the SSG is .45", and the gap between the SSG and hammer had to be 2 turns (.10") to get it to function acceptably.  Despite  the spring being too stiff and harder to cock than I want, the power and air efficiency are showing quite a bit of promise.  I am wondering if a soft spring and heavy hammer might work better.  Too early to tell.

These shots were with 73 grain cast bullets and the power was from 110 to 153 FPE. Fill was 3000 psi.
This is Preliminary Data only, so take it with a grain of salt.  Just getting a feel for how the valve functions.

This is the SSG that screws into the Marauder end cap.  I tapped the endcap all the way thru for 1/2-20 to get a full adjustment range for the SSG. As stated, the spring is too stiff.


Here is the preliminary shot data, but the pressure readings I took might not be 100% reliable. There was some re-filling and resets, so this is more of a compilation.  Still, it is showing a trend for a stiff spring and light hammer. All shots were made with the same SSG settings.
The efficiencies of 1.2 to 1.3 while making 110-130 FPE with a .257 were a pleasant surprise.  The FPE ranges from 110 to 153 FPE.


More work to be done.
Lloyd

[rsterne]

Just looking at your spring, I would say that you need a softer spring, and the 2 turns of gap confirms that.... Something on the order of about 1/2 - 1 turn of gap is more usual.... unless detuning the gun.... Preload is typically about 4-7 lb.f.... I note that your velocity at 3000 psi is very close to the 977 fps you got with a 73 gr. bullet in your initial tests, so you are likely up on the plateau with all those shots.... I'm looking forward to seeing your data for a constant 3000 psi with this bullet, and decreasing the hammer strike to vary the velocity from maximum down to about 600 fps or so.... with corresponding efficiency numbers....

I would try a lighter spring, with roughly 5 lbs. preload, and smaller gap, before I try a heavier hammer.... As long as you have enough hammer strike to max. out the velocity with zero gap, so that you know you are on the plateau, you have "enough" hammer strike.... Adding actual preload will then just make the gun louder.... and waste air....

Your efficiency at 130 FPE should increase at higher pressures, once you get onto the "knee" of the curve.... My Hayabusa, which is pre-SSG, gets 10 shots within 4% ES at 133 FPE from 3000 psi down to 2300 with a 73 gr. bullet, for 1.15 FPE/CI over the string.... I would expect that to increase significantly with an SSG.... When maxed out with that bullet, it got 155 FPE, so we are talking similar rifles....

Bob

[lloyd-ss]

Bob,
Still a bunch of variables to deal with, or more correctly, deciding which variables to vary to get definitive results.

PSI is a given and must be varied.
Hammer stroke right now is .80" and can probably be left as is.
Hammer weight is 44 grams and can be left alone for now.
The spring is too stiff (14.3 lbs/in) so need to fix that by selecting a spring with a lower rate, and adequate travel.
(The setup that produced the above graph probably was about 6.3 pounds un-cocked, and 17 pounds cocked.)
The preload is about 6.3 pounds but can be lighter (along with a lower spring rate.)
The gap needs to be consistent at about 1/2 to 1 turns.

So,
1) choose a spring with a lower rate and adequate travel.
2) set a lighter preload.
3) set a consistent gap.

Then work with varying the hammer strike at each pressure level.

Sounds like a plan.
Lloyd

[rsterne]

Actually, Lloyd, I select a spring rate and preload that allows me to push the velocity up onto the plateau (ie maximum) at whatever pressure, with zero gap, or even a slight preload on the hammer.... This means that once I create a gap of 1/2 - 1 turn, I am operating on the knee of the curve, ie at the practical maximum velocity for that pressure, bullet, and porting.... Then I can reduce the velocity (and at the same time greatly increase the efficiency) by detuning the gun by increasing the gap.... A couple of turns more gap may reduce the FPE by as much as 50%....

You can do it the other way, by keeping the gap constant and varying the preload, but that requires much more adjustment (and often two adjustments in opposite directions) in order to plot the entire velocity vs. hammer strike curve.... This is because as you increase the gap, you are increasing the hammer travel after it leaves the spring, decreasing the distance for acceleration of the hammer, and also decreasing the maximum cocking force (a double whammy in hammer energy).... For example, with your travel of 0.80", if you set the preload at 0.05" the compression (acceleration) distance during cocking (firing) is 0.75".... If you increase the gap to 0.20", that drops to only 0.60" (both in acceleration distance and cocking force).... which results in a great loss of velocity (the effect of the gap is squared)....

Once you determine how the gun reacts to large changes in hammer strike, and decide on a final velocity level in balance with the efficiency desired.... then I reset the gap to 1/2-1 turn with whatever preload is required....

Bob

[lloyd-ss]

I am still working with the tuning and the SSG.  Taking my time (as it is available) doing it and learning a lot.  I have talked to Don on the phone and he says there is also an internal adjustment I can make, if desired, with some disassembly effort.   I have not explored that yet, but probably will.

Bob, I see what you mean about the gap adjustment putting a double whammy on the hammer impact force, by reducing both the hammer spring stroke (the SSG stroke) and the hammer spring compression at the same time.  It makes the "knee" almost become a cliff.

Below are the results from some more preliminary testing at 3000 and 2800 psi.  The power is good.  The cocking force at a maximum of 9.6 pounds is ridiculously low for this amount of power.  The air efficiency is much better than I expected, although I am not extremely confident in my "after the shot" pressure readings.  I have a good gage on the fill tank and a mediocre gage on the gun, and although the correlation between the gages is good, the pressure pulse from firing is kind of rough on the gage hooked up at the gun's gage block.  Because I am keeping the gun connected to the tank during testing, I might just remove the check valve from the fill nipple and read the pressure directly from the better gage on the carbon fiber tank.  Or I could put a snubber in line with the gun's gage. Or do both.

At maximum power, the extra hammer force (zero SSG gap at 3K and 1 turn of gap at 2.8K) is obviously using extra air without gaining any power.  It looks like I need to modify my SSG design so that I can easily adjust both the the spring preload and the gap, rather than just relying on the gap.  Currently, I have to use shims on the SSG spring to adjust the preload so it is a bit of a pain.

This whole discussion does bring up a point about the intended use of a particular gun and how it can be at odds with the obsessive tuning needs of some of us. (I am looking in the mirror right now, LOL, anyone else raising their hand?.......). If this gun were to be used strictly as a hunting gun where only a few maximum power shots were needed, tuning would be pretty easy, and no SSG would be needed.  Extreme power with very light cocking force. A very nice high powered hunting gun.  But now that we have the SSG, it is almost like we (some of the sicker of us, anyway) are obligated to wring out all the efficiency that we can.  I have to stand back sometimes and remember, as I was forced to often at work, that it is important to know when good enough is good enough.  The phrase, " Its time to shoot the engineers and go into production," comes to mind.

But anyway,  I hope I am continuing to provide the information that people are looking for about this valve.  I think it is pretty great all by itself, but it is fun, and a challenge, to explore  its capabilities, and I will continue to do so. Just progressing at my half-fast speed. 
Lloyd
edit - P.S. Looking at this data some more, there is the possibility that this valve wants to be tuned just barely on the top of the plateau, rather than just barely down on the knee.

[Erockrocket]

 Glad you are having fun, Lloyd. Good numbers so far!
Have you ran any tethered strings, I am wondering about consistency?  My 22xx really shines when tethered.
 I recently talked to Mr. Cothran, and pestered him about a SS tube for the Mrod.  Above 3k psi, my 22xx valve really wakes up...lol, I can imagine the Mrod powervalve would too.
 Hope to have our .30 MaxMrod going soon, but life is getting in  the way    
 When we tested with a FFH setup, the tiniest adjustments made for big changes in fps. I need a good weekends worth of tinkering time

[Hobbyman2007]

Lloyd, I found a heavier hammer and lighter spring combo works better than the opposite . Although my build was based on a disco valve the internals I would imagine are pretty close. I'm using a 10 "/lb spring on the ssg and a 60 gram hammer , in a .357 cal I'm producing 140 fpe from a 26" barrel on 2200psi regulated . All ports are at .250".