Don Cothran M-Rod Power House Valve

[Monkeydad1969]

WOW, Lloyd!  Those are very nice numbers.

Congrats on being the first to show us the power of the M-Rod PowerHouse Valve.

Joe

[lloyd-ss]

Thanks guys, and thanks to Don for producing a great valve!  This valve has definitely achieved its intended purpose of a high powered, Marauder rifle valve, that is still very easy to cock.   

The data I have presented is a bit difficult to compare and interpret, so I analyzed and normalized it so that we could compare apples to apples in the various calibers.  Basically, what I did, was set up my spreadsheet with the actual shot data from the 3000 to 3100 psi range for each caliber at the listed grain weight, and then adjusted the pressure for all calibers to 3000 psi, and the barrel length to 30".   So each caliber is showing shot performance data at 3000 psi with a 30" barrel.  Again, this interpolated data is based on the actual shot data that was collected for that particular bullet weight.

Here is the maximum performance for the 3 calibers that were tested, using my particular set up.  Please note that the exhaust port was reworked a bit for the .357 caliber.
Also note that higher pressures and/or heavier bullets will achieve higher FPE levels, and higher pressures and/or lighter bullets will achieve higher velocities.

Final normalized performance:

.257 caliber, 73 gn, SD.158, 3000 psi, 30" barrel.
975 FPS and 154 FPE

.308 caliber, 105 gn, SD.158, 3000 psi, 30" barrel.
914 FPS and 194 FPE

.357 caliber, 131 gn, SD.147, 3000 psi, 30" barrel, (exhaust port modified).
927 FPS and 250 FPE

Personally, I am quite pleased with the performance of this valve.  It produces serious power and is still very easy to cock.
Lloyd

[MichaelM]

thats whats really really awesome is the ease of the power.... easy cocking massive power... so awesome

[rsterne]

Thank you for the Coles' Notes Summary, Lloyd.... most useful.... I have recently been given a Disco PowerHouse valve (thanks, Todd), which has the same size ports as yours.... so I now have a baseline.... It will be going in my existing, and well sorted, Disco Double repeater, where I have three, 1/2" OD barrels to test.... .250 cal TJ's 14" twist and .300 cal TJ's 26" twist, both 25" long, and .357 cal TJ's 26" twist in 28" long.... It may be some time before I get a chance to do anything with it.... but there is no reason that with similar port sizes it should not produce FPE levels proportionate to the shorter barrel lengths at 3000 psi.... I am looking forward to losing the rear cocking hammer which is on the gun currently, and reverting to much easier bolt cocking.... That should also allow me to experiment with an SSG, which I think will work in perfect harmony with the Cothran valve.... This winter's project.... 

Bob

[lloyd-ss]

Bob,
It will definitely be interesting to see how the smaller diameter version of the valve performs in the same calibers.  I see another light weight, but powerful hunting gun in the works.
Lloyd 

[rsterne]

The larger porting of the Cothran valve should allow for an increase in power over the valve I have now.... It's far from a stock Disco valve, at 0.219" porting.... but that extra 1/32" in diameter in the PowerHouse valve should allow for more velocity at the plateau.... My current maximums at 3000 psi are....

.250 cal - 25" barrel - 51 gr. - 1007 fps - 115 FPE
.300 cal - 25" barrel - 70 gr. - 950 fps - 140 FPE
.357 cal - 28" barrel - 132 gr. - 809 fps - 192 FPE

Since my smaller caliber barrels are airgun sizes, I won't have bullets that are as heavy as you did available in .257 cal and .308 cal.... which will limit the FPE....

Bob

[Monkeydad1969]

Looking forward to your results, Bob.  Especially with the SSG.

Joe

[thelast88]

Lloyd, I'm curious, do you have SSG and can you test it, I'd like to see how many shots can you get at lets say around 150-200fpe? 

Thanks

[Erockrocket]

 Those are some pretty awesome numbers Lloyd. I knew you'd wring it out, glad you like it.
Scott and I are taking our MAX .30 Mrod out today, it's 1st trip to the range!  We choose a 32" TJ liner in .294 bore, and added a sleeve of cross directional carbon fiber for stiffness. Slightly modified barrel band holds it taught, gonna see how it groups, see if any other mods are needed.
The power of a Cothran valve is intoxicating, isn't it?

Glad you've now got one to Mr. Sterne, I know you'll be pleased.

My next project will be launching some airrows via a SS2250 tube, and one of Dons Disco valves. I see potential for this valve to power many different air platforms, well. 

[lloyd-ss]

Lloyd, I'm curious, do you have SSG and can you test it, I'd like to see how many shots can you get at lets say around 150-200fpe? 

Thanks

Yes, I do have an SSG for this gun, but I took it out for the last series of testing with all three calibers.  I have thought about putting it back in for the .357 to see how it responds, but it is more a matter of me finding the time to do it.   But if I do get a chance to test some more with the SSG, I will post about the results.
Lloyd

[lloyd-ss]

Those are some pretty awesome numbers Lloyd. I knew you'd wring it out, glad you like it.
Scott and I are taking our MAX .30 Mrod out today, it's 1st trip to the range!  We choose a 32" TJ liner in .294 bore, and added a sleeve of cross directional carbon fiber for stiffness. Slightly modified barrel band holds it taught, gonna see how it groups, see if any other mods are needed.
The power of a Cothran valve is intoxicating, isn't it?

Glad you've now got one to Mr. Sterne, I know you'll be pleased.

My next project will be launching some airrows via a SS2250 tube, and one of Dons Disco valves. I see potential for this valve to power many different air platforms, well. 

Eric, sounds like you have been busy!  I'll be interested to hear how the grouping of that long barrel with the carbon fiber sleeve does.
Lloyd

[lloyd-ss]

AIR EFFICIENCY

The testing that I have done so far with the Don Cothran PowerHouse Valve has been most for power, without much concern for air efficiency.  For this round of testing I installed a Huma regulator into the M-Rod set-up and worked with the hammer force and stroke and pressures to see how the results looked.

The Cothran valve, for the amount of power it puts out, takes only a relatively light tap from the hammer.  It is a balanced valve, so the valve doesn't have to open against the full force from the reservoir pressure, and that is what makes it easy to open.  Also, the maximum stroke of the valve is is .200", and because this is a balanced valve, its operating curve is more of a square wave shape: fast opening....dwell....fast close.  A conventional valve has more of sine wave operating curve: ramp up.... ramp down.  SO the Cothran valve, with the easy opening, the square wave operating curve, and the long valve travel, will always put out lots of air and power.  The previous tests have already shown that.

So this time I wanted to see how the air efficiency might respond to a regulator.  I had a Huma regulator for a Discovery and made an adapter to fit it into the M-Rod.  The pictures show how it was done.  The regulated plenum is 72 ccs, and the high pressure unregulated air is 141 ccs.  A much larger high pressure volume would have been nice, but it seemed that having enough air to get good power was more important.   

For the first round of testing, the reg was set to about 2150 psi, and the front reservoir was filled to about 3150 psi.
Before showing calculations, here is the result:

.357 cal, 105 grain bullets
Shot 1   839 fps, 164 fpe
Shot 1   830 fps, 161 fpe
Shot 1   824 fps, 158 fpe
Shot 1   818 fps, 156 fpe
Shot 1   822 fps, 158 fpe
Shot 1   817 fps, 156 fpe
Shot 1   816 fps, 155 fpe

That is a total of 1108 fpe for the 7 shots with a velocity spread of only 2.7%.  Just for info, the 8th shot was off the regulator and dropped to 792 fps.

So what about the AIR EFFICIENCY?
Because this is an air efficiency test, the two starting tank volumes (HPA and reg) have to be normalized (recalculated) to Standard cubic inches of air (air at atmospheric pressure of 14.5 psi). We will ignore any temperature variables, as they have proven to be insignificant in this sort of testing.

BEFORE THE SHOTS
For the regulated plenum, that is (2150 psi/14.5 psi) x (72 cc/ 16.39 cc/cuin) = 651 std cuin.
For the high pressure res, that is (3150 psi/14.5 psi) x (141 cc/ 16.39 cc/cuin) = 1869 std cuin.
So, filled and ready to go, the gun has 2520 std cuin of air.

AFTER THE SHOTS
After the 7th shot was taken, the pressure in the entire gun had dropped to 1920 psi.
That calculation is (1920 psi / 14.5 psi) x (213 total cc for the gun/16.39 cc/cuin) = 1721 std cuin remaining in the gun.

Therefore, the 7 shots used a total of ( 2520 std cuin - 1721 std cuin ) = 799 std cuin.

AIR EFFICIENCY CALCULATION
Given that the total FPE for the seven shots is 1108, the air efficiency is 1108 fpe/ 799 = 1.39 FPE/Std cuin.

For a hunting gun, an air efficiency of 1.39 is very respectable.

Here are some pics of the current setup.
Lloyd

[rsterne]

Excellent results, Lloyd.... Did you determine what the plateau (ie maximum) velocity is at 2150 psi, or is that what the above velocities indicate?.... In other words, does increasing the hammer strike not increase the velocity and only increase the amount of air used?.... It those velocities are the maximum, then at least in theory, you should be able to get even higher efficiency by dropping the velocity just slightly, to say 800 fps.... or does the Cothran valve not allow such tuning?....

Bob

[Hobbyman2007]

After my own tinkering with a Cothran valve in .357 cal , I would say that 164 fpe would be just about maxed out. This also agrees with a graph you ( Bob ) had posted in the past ( pressure vs fpe per caliber) . Although it shows a max of near 200 fpe that was at 100% efficiency.
At least that's what I remember from the graph ( I may be off 1 to 200 fpe) 
I managed to get 150 fpe from 2200 psi from a 26 " barrel ,mind you it was the disco valve and 80 grain pellets and my tuning skills are not as refined as many others here on the GTA.
That's my two cents and I'm sticking to it.

[lloyd-ss]

This seems to be a very stable setup : Cothran valve, IsoDamp valve stroke limiter, regulator.
During prelim testing with this set up at 2150 psi yielded the following velocities with 105 grain bullets:
5 turns in 840 fps
3 turns in 837
2 turns in 825
1 turn in 815
0 turns 482

I tried shooting a string at 1 turn in for the hammer force, and it did not give any better air efficiency than the 2-1/4 turn set.  This valve seems to react so fast that controlling the pressure with a regulator, or limiting the the valve opening distance is the most appropriate way to control the power output and air usage. 
Here are the numbers from the "1 turn in" set ( same 2150 psi and 105 gn):
Shot 1, 814
2,  820
3, 819
4, 820
5, 812
6, 813
7, 811
8, 785

The final pressure after the 7th shot was 1798 psi, so actually a little worse than the 2-1/4 turn set.

At these settings, and the hammer set to 5 turns in, the vel only increased a tiny bit to 840 fps.  Either the valve stroke, or the psi, would need to be increased to get more FPS. During previous testing, with a full 3000 psi and no regulation I got 964 fps with the same 105 gn bullets (216 FPE), but used an awful lot of air.

There seem to be a lot of ways to tune this valve, and once you find a tune you like, it will probably be best to stick with that tune and forget about the rest.
Lloyd

[Motorhead]

Have an E-main into Don about a valve.
In my own bottled .22 which is regulated and SSG'ed am very curious what it can do when set up to launch @ 21 grain pellet in @ 40 ft lbs.

Perhaps a WAR valve would be better at that power ? .... Tinkeritis is well, how we roll 

[lloyd-ss]

Have an E-main into Don about a valve.
In my own bottled .22 which is regulated and SSG'ed am very curious what it can do when set up to launch @ 21 grain pellet in @ 40 ft lbs.

Perhaps a WAR valve would be better at that power ? .... Tinkeritis is well, how we roll 

Scott,
I am not sure what to say.  Your light hammers and the light hit required by this valve (or more likely, the Disco version) are a natural.  The instant-open square wave operation of the valve is a recipe for efficiency.  But harnessing it seems to require an unconventional approach. Limiting the valve stem stroke, along with a reg and properly sized plenum, might be one approach. 
That tinkeritis will take you to the answer.   
Lloyd

[rsterne]

Lloyd, I wonder if, on a regulated gun, a "variable valve lift limiter" like used in the Korean guns would be useful?.... I see you are using the Iso-Damp to limit the valve lift to 0.080", and you are getting a velocity plateau (3-5 turns) with a very slight drop (1-2 turns), and then a cliff (0 turns).... I wonder at what point the hammer is no longer hitting the Iso-Damp?.... Do you have a feel for that?.... Do you think it's at ~3 turns, or at ~1 turn?.... (my guess would be ~3).... The Iso-Damp should be preventing the valve from releasing wasted air with additional hammer strike, creating an "artificial" plateau limited by the valve lift.... Changing the lift would move the plateau to higher or lower velocity....

If you had a 5/16" ID hole in the Iso-Damp, then you could vary the striker depth in the hammer in or out from flush, and change the valve lift accordingly.... If the screw is 1/4"-28, that would be 0.036" per turn.... I would love to see what varying that over a range of, say 0.044" to 0.116" (2 turns in 1/4 turn increments) would do to the velocity and FPE....

Bob

[MichaelM]

1.39 fpe/cuin is spectacular at that power rating!!!!!!!! actually amazing!!! has ANYONE even come close to those numbers at that fpe level???

[lloyd-ss]

1.39 fpe/cuin is spectacular at that power rating!!!!!!!! actually amazing!!! has ANYONE even come close to those numbers at that fpe level???

Michael,  Thanks!  This valve opens up a lot of possibilities for high powered applications.