Don Cothran M-Rod Power House Valve

[Madmachinist]

Hi I am selling the Powerhouse Valves for the Marauder and for the Disco tubes now.

[Madmachinist]

Hi here's the thing about my powerhouse Valves, they were not designed for low pressures, higher shot counts or smaller calibers.  I made them for big bore guns. I made them for high-pressure. I made them so  depending  on the volume of air that was available to it you would get several powershots before refilling. That what the valve does well. If you want 80 shots per fill this not the valve for you. If you want to use it to take a deer or other game humanely these valves are what you want. I  do appreciate the interest in seeing what you can get out of my valves. But please focus on what they were designed to do.  Thanks Don

[Motorhead]

Hi here's the thing about my powerhouse Valves, they were not designed for low pressures, higher shot counts or smaller calibers.  I made them for big bore guns. I made them for high-pressure. I made them so  depending  on the volume of air that was available to it you would get several powershots before refilling. That what the valve does well. If you want 80 shots per fill this not the valve for you. If you want to use it to take a deer or other game humanely these valves are what you want. I  do appreciate the interest in seeing what you can get out of my valves. But please focus on what they were designed to do.  Thanks Don

Don, that right there is sobering to the reality of the valves R&D / Purpose .... Thank you for clarifying   

[lloyd-ss]

Hi here's the thing about my powerhouse Valves, they were not designed for low pressures, higher shot counts or smaller calibers.  I made them for big bore guns. I made them for high-pressure. I made them so  depending  on the volume of air that was available to it you would get several powershots before refilling. That what the valve does well. If you want 80 shots per fill this not the valve for you. If you want to use it to take a deer or other game humanely these valves are what you want. I  do appreciate the interest in seeing what you can get out of my valves. But please focus on what they were designed to do.  Thanks Don

Don  (Don Cothran),
Thank you very much for clarifying your intended purpose for the Power House valve.  I think the name of the valve says it all.
The testing that I am doing definitely reinforces what you just stated.  This valve is not for getting a lot of low powered shots.

But at the same time, my testing seems to be showing that with some tuning with the spring and hammer, that you can get a lot more of the high powered shots than one might expect.   One thing that I have not done, and maybe I should backup and do this, is to shoot a string with the valve installed in this .257 M-Rod with the stock hammer and spring.  That will give a good baseline to start from. Then, after getting that baseline,  tuning for more air efficiency will make more sense.

From what I have seen with the valve so far, I am VERY impressed. Workmanship, quality, design, and performance are all top notch.
The three things that stand out about the performance of the valve that I have seen, are:
1) Ability to get maximum power with very little effort. (install the valve and go with it.)
2) Extremely low cocking effort.  (No heavy hammer spring is needed.)
3) Air efficiency is much greater than expected for a maximum power valve.  (You can get more high powered shots than expected.)

I am enjoying the testing of this valve and will continue on with it.
Lloyd   
P.S.  I wish the testing was going faster, but the summer outside work is taking up most of my time and the airgun efforts get squeezed in where they can.

[Iamscotticus]

is this valve overkill for a .25 Mrod?

[rsterne]

I don't have one, but unless you are shooting at least the 34 gr. JSB Heavy pellets at around 70 FPE, I would think the answer is yes.... I think at the minimum you will need heavy pellets or slugs to take advantage of the port size and easy opening.... However, testing of this valve is in its infancy (other than by Don), and it may be proven suitable for shooting at 50-70 FPE, with slightly restricted ports and lesser hammer strike.... This is not what this testing is designed to explore, AFAIK.... I believe Lloyd is trying to explore the maximum power capability of the valve, while establishing some tuning methods that will allow good efficiency, at or near those power levels....

When Don says the valve is designed for "high pressure", I would imagine that is because of the sizes he has chosen for the various internal components, to achieve the easy opening, yet firm closing.... This is, after all, a balanced valve, and it would seem to me that balancing one for a wide variety of pressures would be very difficult.... This doesn't mean you cant find a work-around, but the efficiency may be less than what you can achieve with a stock, or modified stock, MRod valve when you are dealing with stock to maybe 50% over stock FPE levels.... This is basically my way of saying listen to what Don is saying, and use the valve for what it is intended, or you may not get the results you were hoping for....

The main advantage of this valve is the easy opening, requiring much less hammer strike.... This means you can make a 100-200 FPE gun out of an MRod (more in larger calibers) without using a spring that is unpleasant to cock.... THAT is the key.... Don, congratulations for developing these valve for the Disco and MRod.... You have done a great service to the development of PCPs....

Bob

[LI Airgunner]

Hi I am selling the Powerhouse Valves for the Marauder and for the Disco tubes now.

How do I order? Do not see these on the web sight, is there a part # ?

[Sfttailrdr46]

  If you are nice to me I will let you see my Marauder when it is done Powerhouse valve, TJ's .30 barrel , WAR SSG and NBH if all works as planned 100+ fpe and a heavy hitting nail driver I use the S510 for tack driving

[LI Airgunner]

If you are nice to me I will let you see my Marauder when it is done Powerhouse valve, TJ's .30 barrel , WAR SSG and NBH if all works as planned 100+ fpe and a heavy hitting nail driver I use the S510 for tack driving

Hmmmm     If your talking about playing with my mill and lathe that's cool 

[Sfttailrdr46]

  My wife will be working the weekend in a couple weeks I'll give you a heads upand maybe we can get together for some shooting at Brookhaven range. If this build goes well I may try to build a .308 Marauder with the same set up and a 26" barrel and extended air tube

[LI Airgunner]

My wife will be working the weekend in a couple weeks I'll give you a heads upand maybe we can get together for some shooting at Brookhaven range. If this build goes well I may try to build a .308 Marauder with the same set up and a 26" barrel and extended air tube

Sounds good.  Weekends are tough as I have a 5 yr old, I'm going to have to put a big dent in the honey do list

[lloyd-ss]

After thinking about Mr. Cothran's discussion about the  intended purpose of this valve, I re-thought what might be needed for some baseline data. Given that I have a nice .257 cal 30" barrel on the gun, lets make the assumption that the .257 barrel was installed with a full bore diameter transfer port, and that the spring and hammer were left as they came from the factory. What kind of power and shot count would a gun like that get?

If you take a look at sets number 9 (93 gn bullets) and 10 (73 gn bullets), below, you will see the power and shot count using a very straightforward installation with factory spring and hammer.  Note that the hammer striker is adjusted to give maximum hammer stroke, and that the hammer spring is adjusted to give minimum hammer force.  That combination gives a very easy to cock, high powered airgun.
Both strings start with a 3450 psi fill (yes, I know, higher than recommended by the factory, but I have done the analysis and am comfortable with it for myself.)  At that sort of fill pressure, I don't think a factory valve and hammer set-up would even open.
The hammer has to be set to open the valve at maximum fill pressure, and then as the reservoir pressure drops with each shot, the hammer strike becomes more than enough to open the valve on each successive shot.
The air efficiency for the shots ranged from a high of 1.1 (for the 93gn) to a low of about .72 (for the 73 gn) depending on where you think the end of the string should be.  The air usage per shot was an average of the total for the string.

I thought it would be interesting to compare this set up with stock hammer and spring to one with an SSG.  This thread is about the Cothran valve, and not the SSG, but seeing if the SSG can improve the valve's efficiency is  a valid question.

String 7 uses the same setup as strings 9 and 10, but it uses an SSG instead of the stock hammer and spring.  And indeed, the efficiency of the valve does improve.  That means the shots are within a tighter velocity spread.The SSG seems to help most where the pressure is dropping and the hammer is hitting harder than necessary.  The SSG takes the edge off that excess hammer force.
Even though all 3 strings have 7 shots, the spread on the one with the SSG is much tighter.  I think the SSG can be adjusted to give either more shots, or a tighter velocity spread.

[rsterne]

Great results, Lloyd.... It is interesting to see what the gun does when cranked up to the limit.... Considering that the use for a .257 cal is usually long range, and requires a low ES (less than 2% at 100 yards) to reduce vertical stringing, with the gun tuned this way you would really need to tether it to a regulator, IMO.... Using a 4% ES, you only get 3 shots without the SSG and 4 with it.... and only 2 shots within 2%.... I notice that the FPE at 3000 psi (doing a bit of interpolating) is about 166 FPE with the 93 gr. bullet (I predicted 170, remember), and 154 with the 73 gr.... I think you could probably tune the gun to produce a 7 shot string within a 4% ES at about 150 FPE average with the 73 gr. bullet, if you start at 3450 psi.... Basically, you would be tuning it right on the knee of the curve on shot #4 at 3000 psi, so the velocity from shots 4-7 would stay the same, but that of the first three shots would drop, producing a bell-curve....

There is no doubt that getting over 180 FPE from an MRod in .257 cal is quite an accomplishment, even if it took 3450 psi and a 30" barrel to do it.... WELL DONE to both you and Don !!!

BTW, I see you used the average pressure drop to calculate the efficiency of each shot.... I think if you had looked at the gauge after each shot, you would have found that it dropped more slowly initially, when the pressure was higher, and more quickly towards the end of the string.... That seems pretty normal for an unregulated PCP.... Although it's not a huge difference, it does usually occur.... so the efficiency at high pressure is likely a bit more than your numbers, and at low pressure not quite as good....

Bob

[lloyd-ss]

There is still a lot to learn.  Mr. Cothran worked on the development of this valve for quite a long time, and I think learning about it should also be done in an un-rushed, thoughtful manner.  Don did mention an internal adjustment that can be made and I will probably try that the next time I have the valve out of the gun.  I believe the valve is set to a maximum setting right now and I'd like to see what happens with some adjustment.

You'll notice that there are some missing "set numbers" in the spreadsheets.  Those are the sets where I have been adjusting the hammer and spring settings to find a good adjustment for an actual set.  It does seem that there is still more of a cliff than a knee in the curve and that the valve does not exhibit the usual inverted bathtub velocity curve of a standard knock-open valve.  At this point I am going to avoid getting too deep into the tuning, which can be very time consuming (especially when working with a valve that behaves with such different characteristics) and instead try a couple of other barrels on the gun.  I think folks are interested in numbers from larger calibers.  I took another look through my collection of barrels again and saw that the 23" long  .308  has the same port configuration as the .257.  All I need is a different nose for the bolt and I can give that a try. I found the bullets, too. Powerwise, the shorter barrel length might offset the advantage of the larger caliber, but we will see.  The 28" .357 will be after that.

I think thoughts about trying this in a regulated configuration are definitely worth consideration.   The power levels at 2400 psi are still very high and regulating to a pressure in that neighborhood might be worth a look.  I have found that if you stay away from the "transition" area in the curve, that the velocities are super consistent at any given pressure. A regulator could take advantage of that.

Lloyd

[rsterne]

Sounds like a reasonable direction to continue.... looking forward to the results.... I see no reason that the valve won't work well in a regulated setup, with the correct hammer strike.... I would expect about 200 FPE at 3450 psi (with 110 gr.) in .308 cal.... Heavier bullets should result in higher FPE, of course.... A 150 gr. bullet in the 23" barrel at 3450 psi should hit about 220 FPE, I would guess.... My DAQ .308 Exile, with a 24" barrel, had the same size ports, and shot 185 FPE with a 113 gr. bullet at 3000 psi, just for comparison.... However, it used a hammer that weighed 190 grams, with 1.62" of travel, and a cocking force of over 20 lbs.... 

Bob

[lloyd-ss]

Getting ready to do some testing with the .308 barrel.
Here are a couple of side-by-side comparison pics of the .257 and the .308 barrels.  The .308 has a cross sectional area advantage .0745 sq in vs .0519 sqin, the .257 barrel is 30" long and the .308 is significantly shorter at 22.6" long.  The barrel ports on both barrels are almost identical, but the .308 is a little wider at .230 vs .185 for the .257.
The sleeve for the bolt is almost finished.
We'll see what happens.
Lloyd

In both photos, the .257 barrel is at the top of the picture.

[rsterne]

The maximum FPE potential of a barrel is proportional to the barrel volume.... For the .308 barrel that is 1.68 CI, while for the .257 barrel that is 1.56 CI.... an 8% theoretical advantage for the larger caliber at the same pressure.... However, the exhaust port on the valve is equal to the bore area of the .257 cal, but smaller than that of the .308 cal.... It will be interesting to see which has the greater effect, or if they will cancel out....

Bob

[lloyd-ss]

Bob,
I think the operative phrase is "maximum FPE potential."  We know that long thin barrels exhibit definite diminishing returns as they get longer.  The .257 is 117 diameters long and the .308 is only 73 diameters long.  The .308 is still gaining about 12 fps per additional inch of barrel length, while the .257 is gaining about 8 fps/in of barrel length, so the .308 should have the FPE advantage. I haven't shot the .308 with the Cothran valve yet, so I don't really know......yet!
Lloyd

[rsterne]

Yep, Lloyd, I agree 100%.... IIRC, however, you stated that the exhaust port on the Cothran valve is 0.257", which is 100% of the bore area on the .257 cal, but only 70% of the bore area on the .308 cal.... My gut tells me that the .308 will have more power (and that is what I predicted in post #134).... but if it doesn't, I think the port size is the explanation....



*grabbing my popcorn for the next round*....

Bob

[lloyd-ss]

I got the new .308 bolt and the .308 barrel installed, but there was a moratorium on loud noises    this evening, so no testing until tomorrow   .

Anyway, here are the details on modifying the .257 bolt to work with the .308 barrel.
As you can see in the pictures, I just made a sleeve to fit the breech of the .308 barrel, that fits onto the .257 bolt . Because the front end of the sleeve only has .025 wall thickness, I left the rear portion of the sleeve thick, at .375" dia.  That provided enough material to machine an internal o-ring groove to accept a 6mm I.D. x 1mm cross section o-ring, and also a small set screw to secure it to the existing .257 bolt probe.  The fit is good, and the cocking and cycling action is normal, as it should be.

Because the rear portion of the sleeve is 3/8" dia, this method will not work if a magazine is to be used. But for single shot loading, it is fine.

Here are the components for sleeving the .257 bolt tot eh new size of .308.


Here the bolt is, with the .308 sleeve installed.  The sleeve can be removed to change the bolt back to .257 cal.


The bolt and sleeve are in the full forward position.  This shows how the sleeve has plenty of clearance, so long as you are firing single shot.  If you are using a single shot tray, the tray would need to be slightly modified to cycle properly.