Don Cothran M-Rod Power House Valve

[rsterne]

Here is a plot of Lloyd's Data from the above tests with the 73 gr. bullet, at 2800 and 3000 psi, with Velocity and Efficiency plotted against the SSG Gap....



You can clearly see the classic "plateau" in the velocity curve, which is the maximum velocity for that bullet at that pressure.... As Lloyd says, the "knee" is very sharp, making the "downslope" more of a cliff.... however, that is really only a function of the relatively coarse adjustments of the gap.... I often adjust the gap in my SSGs only 1 flat (1/6th turn) at a time, and for fine tuning, even less than that.... Of course if you use a weaker spring with more preload, the adjustments become coarser....

Now that Lloyd has hard data for the maximum velocity at 2800 and 3000 psi, and there is already a considerable gap (1T @ 3000 and 2T @ 2800) where the knee starts, I think he can reduce the preload, or go to a weaker spring, so that the knee occurs with a smaller gap.... Making finer adjustments of the gap will give more data points for the velocity, and particularly for the efficiency, and I would expect to see the efficiency peak at a somewhat lower velocity, but the fact it is high on the lower end of the plateau and drops as the velocity drops may be a characteristic of the Cothran PowerHouse Valve.... The one thing I have found with the SSG is that the efficiency can be much better on the knee of the curve, and on the plateau, providing a gap is maintained.... I think without the SSG, once you are on the plateau, hammer bounce is rampant, which causes the efficiency to decrease rapidly with increased hammer strike.... I have not fully explored this region of operation of the SSG, but it makes sense that it may mean that you can operate a lot more efficiently on the plateau than without it, providing a gap is maintained.... This could mean maximum power tunes may be easier to achieve, with better shot counts, than without the SSG....

As I mentioned when I first introduced the SSG, I think using it in combination with a balanced valve (which the Cothran is).... could usher in a new era in easy to cock, and yet efficient, high-power PCPs.... It looks like that prediction was right on the mark.... Has anyone ever seen a .257 produce 140+ FPE at an efficiency of over 1.5 FPE/CI before?....

Incidently, Lloyd, if you had data for a gap of 0.50 & 0.75 turns @ 3000 psi, I think the efficiency may have even been higher than 1.24....

Bob

[Sfttailrdr46]

I am curious to see just how well this works out in my .30 Marauder with 20" barrel

[rsterne]

Denis, it may make some sense to use a heavier hammer and lighter spring with a PowerHouse valve, because the Force Reduction system makes the valve easier to crack (requiring less energy) but the way it is vented inside increases the closing rate (I think) and the relative large valve stem diameter also contributes to that.... so the increased hammer mass, which increases dwell, could counteract that.... while the light spring reduces the energy (and dwell) as required by the easier to open poppet design....

This is just a guess, but could explain what you found by experiment....

Bob

[Hobbyman2007]

I knew you knew what I meant. I love the valve . Just took way more lead to get it figured out than I wanted. Great work Lloyd. I'm sure Don will be happy with the increased sales of his mrod valve . Big bore rifles with efficiency of a small bore , happy times for all.

[Erockrocket]

 After reading this , I am wondering if a heavier hammer will help in my .357 2260 using a smaller powervalve. I hit a wall with fpe, while still using a managable hammer spring. When the fill pressure is higher, the valve closes much quicker. At under 3k it seems to be wasting more air because of the heavy hammerspring, and bounce.
 I guess I need to revisit my .357, see how a ssg, or ffh may help get some extra fpe.
Good reading everyone!

[rsterne]

The only way to tell if you can get more FPE is to plot velocity vs. hammer strike, as in the graph above.... If you have a plateau, then no amount of additional hammer strike will increase the velocity.... The only way to get additional FPE is from more pressure, or larger ports (or a longer barrel)....

Bob

[lloyd-ss]

All,
Thank you for contributing your thoughts on this project.  As always, this kind of camaraderie is what makes the GTA the special place that it is.

Bob,
Thanks for the detailed analysis.  That gives me additional direction on what to do next to take this to the next plateau.  Ouch!
The efficiency AND the light cocking effort are a both a big deal, and the SSG and Cothran Valve really seem to compliment each other. 
As I already stated, my next step is to modify the SSG to make it easy to adjust the spring preload while still keeping the gap to a minimum.  There will be more data to analyze before too long.

Thanks,
Lloyd

[rsterne]

Lloyd, you are exploring one thing with the SSG I have never done.... On all my SSGs, I kept increasing the preload until the velocity maxed with no gap.... Any "reduction" in gap (negative gap?) past that results in preload, of course, and an instant air hog.... but with no increase in velocity because you are already on the plateau.... What I am seeing in your results is that if I try more preload, so that I can hit the plateau while I still have a gap.... there may be more efficiency available, even at the maximum FPE level.... This is something I never considered, because without an SSG, getting even close to the plateau wastes air.... Certainly with the Cothran Valve, you can push up onto the plateau (ie use maximum power) and still get extreme efficiency.... I am now wondering if the same may well apply with a conventional valve....

It just goes to show that we are always learning.... and you never know where the next advance may come from.... You can bet I will be exploring this when I build my new Disco Double....

Bob

[Sfttailrdr46]

I am watching avidly because this whole project is a learn as we go I am 3 or 4 steps behind you Lloyd and as soon as I get my goodies from crosman I will be sending you a .25 bolt to sleeve for me unless you can just fabricate and send it to me I will just do a paypal or CC# which ever works

[shorty]

Bob,
Can you explain the 3 axis graph a little different for people like me.

From what I am getting from it on the 2800psi charge there is a bell curve in regards to efficiency with a drop in FPS at a certain point with gap adjustment ?

I always thought that more gap not only reduced fps but increased efficiency. But from what I see from your data that's not true ?

Maybe I am looking at it wrong.

[rsterne]

Velocity (solid lines) is on the left axis.... Efficiency (dotted lines) is on the right axis.... You are correct, that with the Cothran valve there seems to be a bell-curve on the efficiency graphs.... I have seen that before, when you make an EXTREME reduction in the FPE (in this case, from 140+ FPE to just 17 FPE).... and it doesn't matter whether you are using an SSG or not.... What is happening is that the velocity gets extremely low but you are still using SOME air.... This drop in efficiency at low FPE levels could also be an idiosyncracy of the Cothran Valve.... Part of the problem, as Lloyd stated, is that he is only reading the pressure after the shot to 10 psi, and on a single shot, not the greatest for accurate determination of the efficiency.... More data points, closer together, would form a better trendline.... We are, after all, working with an unknown here, in terms of how the valve reacts to varying hammer strike.... Here are two examples of a Regulated QB, with a conventional hammer spring (no SSG)....

 

Imagine continuing the velocity down to about 200-300 fps, and the efficiency would be terrible.... The peak efficiency in both cases is about 2 turns below the start of the plateau....

Bob

[shorty]

Strange but, I can see why chasing hammer weight now might be very important. Excellent data.

[rsterne]

Yes, we are learning with every set of data.... and sometimes that just gives us more questions.... but also opportunities....

Bob

[shorty]

Maybe that increase in gap with decreased velocity curve is the direct reflection of hammer bounce. More or less, possibly a way to calculate the efficiency of an ssg or short stiff spring in regards to valve re-opening hammer bounce.

Pretty interesting

[Erockrocket]

The only way to tell if you can get more FPE is to plot velocity vs. hammer strike, as in the graph above.... If you have a plateau, then no amount of additional hammer strike will increase the velocity.... The only way to get additional FPE is from more pressure, or larger ports (or a longer barrel)....

Bob

I always reached a point of the spring being so heavy, the sear couldn't hold the hammer. Thats why I am thinking less spring, more hammer weight may over come the balance of the valve, at least at higher fill pressures. I  did reach 200 fpe with my small SS 2260 tube setup, plenty for that platform. 
The Mrod tube has alot more volume behind it, but 3000 psi is tame for this valve setup. It really wakes up at higher pressures.
 Enough babbling from me, I am still trying to take it all in.

[rsterne]

Sorry, shorty, I didn't understand that.... Basically, whether we are talking an SSS, SSG, or a conventional hammer spring setup, once you detune the gun to a fraction of what it is capable of, there is no hammer bounce, because the first hammer strike is barely enough to open the valve, let alone a second one.... The drop in efficiency is simply caused by the drastic drop in velocity and FPE of the much less powerful shots....

Bob

[Stikman]

Thanks for all your efforts Lloyd...this info says much about the PowerHouse valve.

Anyone have any idea when they will start shipping? Ok I will ask Don myself...

Hey Don, when will you start filling orders? Us power hungry BB gun guys are anxiously awaiting the release of your innovative PowerHouse Valve.   


Gene

[Monkeydad1969]

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".

I agree.  Lighter spring, heavier hammer.  That's how my .25 and .30 PowerHouse 2260's are set up.  Again, using a Disco hammer and cut down 13xx spring cut down 3 coils shorter than the original Disco spring...not the new springs they use.

Joe

[rsterne]

Joe, a 13XX spring shortened 3 coils must have very little preload in a Disco?.... or does it actually have a gap to the hammer when uncocked?.... If it still has preload, even a little bit, I would be tempted to use an original Disco spring and shorten it until it has a slight gap (negative preload).... The efficiency should increase, by eliminating hammer bounce.... Alternately, you could use a 22XX spring with preload and an SSG....

Bob

[Monkeydad1969]

With it shortened 3 coils shorter than the original Disco spring and the RVA turned in 2-3 turns from when the threads first engage, I can hear the spring slide back and forth if I tilt the carbine up and down.  That easily gets me into the 45fpe range.  That is with the JSB Kings.

Joe