Don Cothran M-Rod Power House Valve

[lloyd-ss]

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

Bob, I am pretty sure the hammer is hitting the IsoDamp in all cases except for the "zero turns in" when the velocity falls off drastically (482 fps).  The air used with each shot is a good indicator of that, and the air usage also fell off dramatically with the zero turns shot.  The C1100 IsoDamp is a fairly hard damping material (about like a medium-hard vinyl flooring) and judging by the velocity consistency, provides a uniform stopping point for the hammer, and therefore a consistent valve stroke.  The IsoDamp absorbs the excess hammer strike and turns the energy into low grade heat, and essentially kills the hammer bounce.  The IsoDamp creates an in-elastic collision instead of the usual elastic collision of a hammer hit. The slight drop in velocity with the shot string is mainly due to the slight drop in plenum pressure as the HPA supply drops in pressure.
Also please note that the "zero turns in" setting is actually a lot softer than a normal zero turns in.  The threaded hole in the M-Rod end cap has been drilled out and tapped all the way thru so that the spring adjuster can be backed out completely.  "Zero turns in" in this set-up is actually zero preload on the spring, which is at least 1/4" less preload  than a factory set-up at its lightest setting.  So again, a very light hammer hit.

I had planned on re-installing the adjustable striker in a manner that allows setting the valve stroke to different lengths, but I also need to re-install the lighter hammer to get the hammer force into a more useful operating range.  If the striker can be adjusted so that it just barely cracks the valve open, I think the air efficiency will climb even higher.  We will know shortly.
Lloyd

[Motorhead]

JUST AN FYI ....

Don responded to my E-mail stating this:

Hi I have them for sale. Total with shipping is $161.00. Thanks Don


So ... if you want one, seems there NOW available.
Use: doncoth@comcast.net

[rsterne]

Lloyd, thanks for that response.... If you feel that the hammer is hitting the Iso-Damp in all cases except the zero preload, then I assume the slightly increased velocity going from 1 turn up to 5 turns of preload is a few thou more lift from the heavier hammer strike compressing the Iso-Damp more before coming to a full stop.... Is the air usage nearly constant as well, from 1 to 5 turns?.... I would think so.... I figured the slight velocity drop during the string was due to regulator outlet side pressure drop from inlet side (reservoir) drop....

I realize that using an adjustable striker changes the hammer stroke, but if you use enough preload so that the hammer face is hitting the Iso-Damp all the time, then the stroke variation should no longer be important (as the valve lift will be whatever the Iso-Damp will allow).... This should allow you to plot velocity (and efficiency) vs. lift at your operating pressure, which will tell us a LOT about what is happening.... I realize that with increased lift comes increased dwell, of course, but the info will still be great to have.... You should also be able to plot efficiency vs velocity/FPE.... 

Bob

[Motorhead]

Just hung up phone call with Don C talking about USES not designed for the valve 
What i took from it was that the "Balanced" aspect of it requires VOLUME of air to be behind the shot and / or within a plenum space of a regulated configuration.  Don stated that too great a pressure drop during a shot would have valve unbalanced & not really wanting to close itself from loss of differential pressure that is keystone to the design function.

As we talked about my intended use and parameters of being regulated and lack of sufficient plenum as currently set up ... correct function & potential of the power house valve likely would not be met used at such a SUB POTENTIAL power level 

That said ... with a clean slate and a virgin action having modifications DESIGNED around the use of the valve it sounded like it could be made to work quite well !!

Just some tidbits gleaned.

[rsterne]

Sounds about right.... To paraphrase that, the valve needs a relatively constant pressure on the inlet side to close properly.... If the volume entering the valve (ie flow rate into the valve) is too restricted, there will be a larger pressure drop inside the valve during the shot.... In the case of too small a plenum, the same thing occurs.... If those conditions lead to slow closing, then I would expect the valve to waste air when used that way.... compared to starting with the same pressure but a smaller pressure drop during the shot.... This means that for best efficiency, you want big ports on the inlet side, and a big reservoir/plenum....

Lloyd is only using a plenum of 1/2 cc per FPE, and is still getting 1.39 FPE/CI.... Averaged out, Lloyd's most recent test used (799/7) = 114 std. CI of air per shot.... At 2150 psi, that would occupy (114x16.4)/(2150/14.5)= 12.6 cc of HPA.... The plenum volume was 72 cc, so the pressure at the end of the shot was 2150x(72-12.6)/72 = 1774 psi.... The average pressure during the shot was 1962 psi, less than a 9% drop.... The only way to be sure that was not affecting the efficiency would be to double the plenum size and see what happens.... On the other hand, at 1.39 FPE/CI, do we really care if we can make it better?.... 

Bob

[lloyd-ss]

More Air Efficiency Experimentation with a Real World Happy Ending 

This batch of shots and data continues with the same set-up as the last batch, using the IsoDamp material to stop the hammer travel and limit maximum opening of the valve.  The Cothran Powerhouse valve seems to open very quickly and efficiently in a more-or-less square wave type of motion.  The idea of this testing is to arrest the hammer travel at a specific distance (specific valve opening distance) using a material designed to absorb the excess hammer energy and dispate it as low grade heat, instead of rebounding it back into the hammer and causing air-wasting hammer bounce.  It basically makes the hammer function like a shot-filled dead-blow hammer.

The goal in this experiment deviates a bit from Don's main intent for the valve.  Instead of going for maximum power, the attempt is to achieve moderate power at very good air efficiency.  That goal, as well as Don's original goal, have all been achieved.

This setup consists of a stock Marauder rifle air tube, divided into a front HPA section of 141 ccs, and a rear regulated plenum of 72ccs.  In between the two sections is a Huma regulator.  In order to adequately monitor the air usage with each shot, I needed to know how much the pressure dropped in the regulated side after each shot.  That meant that the automatic refill of the plenum thru the regulator had to be stopped with a shut-off so that the after-shot pressure could be read with the digital gauge, and then, the shut off could be opened to allow the plenum to fill back up for the next shot.  As shown in the picture, I added a socket head screw (The Allen wrench in the pic is used to turn the re-fill function on and off) that forces a steel ball into the exit passage of the regulated air to stop the flow.  The ball is forced into the exit passage in the adapter; it does not apply any force to the Huma. 

Socket head screw used to stop the re-fill into the plenum from the Huma regulator.


The following table shows some of the shot data that I collected to help determine usable combinations of hammer spring preload and maximum valve opening.  All testing was done at 2200 psi with 105 grain bullets.  Arbitrary, but realistic.  Because I was only looking for moderate power, valve opening was limited to  .054" and .071".  Various spring preloads were tried so that the velocities and air usage at each setting could be analyzed.  The valve is capable of a full .200" of opening which was unnecessary for this experiment.  The pressure readings only pertain to the regulated plenum of 72ccs.  You can read the pressure drop in the plenum with each shot.  Some of the air efficiency readings are quite impressive!

Particulars for Set number 19:
07-18-2016  M_rod with Cothran Power House valve and other mods. Stock spring.                           
27.7" .357 barrel, T-port .293 (67%)ex port transition to .275 x .324 (85%) oblong.                           
53 gram hammer with adjustable VALVE stroke. IsoDamp to stop hammer.                           
Stock spring (.049 wire x 2.35 lg x 14 coils).  Valve throat  .358 x .175 stem (77%).                           
Huma reg installed. Total air volume 213cc:  141cc unregulated, 72cc regulated.                           
Valve stroke (full-open distance) limited by IsoDamp C-1100 Hammer travel limiter.                           



After studying the data I decided to try a shot string using a setting of .054 valve travel, and .225 (4-1/2 turns) of hammer spring preload.  That is TOTAL hammer spring preload and is similar to a factory gun with the hammer spring adjustment backed all the way out CCW to the minimum hammer force.  In other words, this is a very light hammer hit and a very small amount of valve opening.  But golly, does it work well!
I chose to use the .054 valve opening and 4-1/2 turns based mainly on shots number 19-3 and 19-4.  This is a bit up on the plateau for a regulated gun, but the efficiency does not suffer, and staying up on the plateau with this valve  seems to give a more consistent velocity.  Once you come off the plateau, such as with shot 19-2, the velocity can vary a bit.  Keeping the hammer force high enough helps ensure consistent velocities.

Shot string with regulator set to 2200 PSI.
Particulars for shot string, Set number 20:
07-21-2016  M_rod with Cothran Power House valve and other mods. Stock spring.                           
27.7" .357 barrel, T-port .293 (67%)ex port transition to .275 x .324 (85%) oblong.                           
53 gram hammer with adjustable VALVE stroke. IsoDamp to stop hammer at .054" valve lift.                           
Valve stroke (full-open distance) limited by IsoDamp C-1100 Hammer travel limiter.                           
Stock spring (.049 wire x 2.35 lg x 14 coils).  Spring preload set to 4.5 turns (.225").                           
Valve throat  .358 x .175 stem dia (77%).                           
Huma regulator installed. Total air volume 213cc:  141cc unregulated, 72cc regulated.                           
Starting PSI in unregulated front end 141cc tank = 3150 psi.  Starting PSI in the regulated plenum = 2200 psi.                           
Final system PSI in both the unregulated tank and regulated plenum = 1874 psi.                           


 
Additional information:
During the first part of the shot string (shots 1 thru 6)  I stopped the refill from the front HPA chamber at 2200 psi each time to improve the validity of the data. Shots 7, 8, and 9, show the effects of the air pressure below the regulator set point. 
Starting pressure was 3150psi in the front HPA 141cc chamber, and 2200 psi in the rear regulated plenum. 
After the last shot was taken and the plenum pressure drop was read, the plenum was allowed to refill and the final system pressure equalized itself at 1874 psi. 
That calculates out to a system air efficiency for the 9 shots at 1.62 FPE per std cuin of air, which is slightly different than the "average" air efficiency.  But anyway you look at it, those air efficiency numbers are VERY impressive for a 150 fpe airgun.
Don's valve, with some assistance from the Huma regulator, and a bit of special tuning, really gives a happy ending. 

Lloyd

[Monkeydad1969]

Great going!

Joe

[Motorhead]

Lloyd ... outstanding work !!

[lloyd-ss]

Thanks guys. This valve is more versatile than I originally thought and can be tuned for different applications.

[Stikman]

Nicely done Lloyd...

[MichaelM]

wowza!  makes me wanna get one for the disco..... maybe a 22 heavy pel... maybe try to get 50 fpe in .22   

[rsterne]

Excellent results, Lloyd.... It looks like the first shots, at 0.054" lift, reached the plateau at 4 turns, with no velocity gain at 4.5, and only a slight loss in efficiency.... At the larger 0.071" valve opening, I don't see a plateau yet, it would have been good to have at least one more preload setting at 5.0 turns to see if the velocity was still increasing above the 839 fps of shot 19-9, or equalled it, indicating the plateau starts at 4.5 turns....

The shot string, at 0.054" lift and 4.5 turns, showed an ES of only 21 fps over the first 7 shots, with #6, strangely, being the lowest.... perhaps just normal variation.... Achieving over 150 FPE at over 1.50 FPE/CI for those 7 shots is quite a spectacular result indeed.... It shows that the Cothrane valve can be used in a regulated setup and obtain great efficiency....

Bob

[lloyd-ss]

Bob, Yes, it looks like I might have stopped the .071 lift testing a little prematurely by not trying a shot with 5 turns of spring preload. However, some of the other test shots that I took that I have not posted, indicated that 839 fps was about the max vel for this bullet at 2200 psi.  SO I think the 839fps is up on the plateau.  I might give that another try, though.  Extra data never hurts.

Plus, it might be interesting to approach this from a different angle and find out what settings: regulator pressure, valve stroke, and spring preload, will yield the highest velocity 5 shot string with those 105 gn bullets with maybe a 25 fps ES.  Seems like that would be useful for a hunting tune.
Lloyd
 

[rsterne]

Now that you know you have two major variables (pressure and lift), you will always be able to find where the plateau starts with any given combination.... and you have determined that the best place to be is just on the plateau.... so there will be a large number of possible combinations of pressure and lift, and each one will have a different velocity and efficiency.... If you have the time and inclination, my approach would be to pick a pressure (eg. 2200), and try various lifts that produce from, say, 120-200 FPE, set each up just on the plateau, and record the FPE/CI and velocity.... Graph those (vs. lift), pick a different pressure and repeat.... You will end up with several curves, at different pressures, of velocity vs. lift, with another set of curves of FPE/CI vs. lift.... It would then be a simple matter of deciding what FPE will give you the number of shots you want, and pick the combination of pressure and lift that gives the best efficiency....

I realize you probably aren't interested in generating that much data, I am presenting this as more of a "how-to" to show guys how they could systematically find the best combination.... Realistically, almost any combination will work, and work well, from what I can see....

Bob

[lloyd-ss]

Bob,
Good methodology plan.  I am counting my bullets right now, and luckily, don't have too many left. 

After I wrap up the .357, I am going back to the .257 and see if it responds in the same manner.
Lloyd

[rsterne]

Now THAT (.257) I am looking forward to, as you know.... 

Bob

[lloyd-ss]

Me too!  I have a LOT of data from the current .257 M-Rod set-up (bottle gun with reg), and it is a real air hog (with a BIG spring) when the goal is big power (130 fpe).  So this will offer a real side by side comparison of the Cothran Power House valve vs a more conventional regulated arrangement. I am expecting the Cothran valve to beat the snot out of the conventional valve for air efficiency, and possibly for power, too!   
Lloyd

[oldpro]

Lloyd I didnt read threw every post on the 10 pages so forgive me if this question has already been answered. Can you make a traditional bell curve with this valve? Also I noticed your dampning device and it got me thinking about the very effective adjustable poppet adjuster on the NBH it is spring loaded and is depth adjustable for rebound etc. I can explain more if you give me a call. Fantastic work as usual my friend!!!  Heres a video This hammer system was even more effective than the SSG but was extremely hard to explain to customers how to adjust the poppet the hammer striker and preload etc. so i canned it. Anyway its yours to use and I have parts left over if you want them to play with.

[Monkeydad1969]

Lloyd I didnt read threw every post on the 10 pages so forgive me if this question has already been answered. Can you make a traditional bell curve with this valve? Also I noticed your dampning device and it got me thinking about the very effective adjustable poppet adjuster on the NBH it is spring loaded and is depth adjustable for rebound etc. I can explain more if you give me a call. Fantastic work as usual my friend!!!  Heres a video This hammer system was even more effective than the SSG but was extremely hard to explain to customers how to adjust the poppet the hammer striker and preload etc. so i canned it. Anyway its yours to use and I have parts left over if you want them to play with.

Seems easy enough.  Don't see why that wasn't simple enough for people to follow.

Joe

[lloyd-ss]

Lloyd I didnt read threw every post on the 10 pages so forgive me if this question has already been answered. Can you make a traditional bell curve with this valve? Also I noticed your dampning device and it got me thinking about the very effective adjustable poppet adjuster on the NBH it is spring loaded and is depth adjustable for rebound etc. I can explain more if you give me a call. Fantastic work as usual my friend!!!  Heres a video This hammer system was even more effective than the SSG but was extremely hard to explain to customers how to adjust the poppet the hammer striker and preload etc. so i canned it. Anyway its yours to use and I have parts left over if you want them to play with.

Travis,
Thanks for the generous offer, I will send you a PM.  I watched the video this morning, and like Joe said, the tuning process sees pretty logical and you did a good job explaining it. I am anxious to give one a try.
Lloyd