Nice looking collection of parts Bob. Any idea where Travis got that wood stock from ?
You wouldn't want to use 4500 psi in the tube,, but with a regulator between you are probably OK.... It's too bad we can't get burst discs at around 3800 psi, but they jump from 3K to 5K.... although from England you can sometimes get 4.5K ones.... It you had a regulator failure on a full, 4500 psi bottle, you could end up with that in the main tube.... The safety margin is probably high enough to not cause you injury, but you should degas and disassemble the gun and replace the valve mounting screws as they will have been overstressed.... I don't know what the limit if for pressure on a MRod setup, it's almost impossible to calculate the failure point of the valve screws (which is likely the weakest point) because the heads of the screws are supposed to be in shear, not the shank.... I don't know of anyone who has tested an MRod tube, with valve and fill fitting, to failure, perhaps Lloyd will do that now that he has his new 30,000 psi test rig built.... I think Lloyd uses up to 3500, and I'm pretty sure Travis uses a 250 bar tank unregulated on the FLEX.... so maybe they will chime in....Bob
While it's nice to be able to "in theory" remove a regulator/bottle assembly from a PCP, in practice you are VERY likely to blow the O-rings on the end of the reg. because once the reg. is unscrewed, you still have pressure in the reservoir in the gun.... Some tank blocks (eg. the QB79) have a vent hole to bleed off the CO2 left in the gun when you start unscrewing a CO2 tank, and at those pressures, you don't usually ruin the O-ring.... However, it has been my experience that unscrewing an HPA regulator from a QB tank block will blow the O-ring as it tries to extrude it through the small vent hole.... In addition, it can be quite hard to even turn the reg. if there is still pressure in the gun.... which in itself should warn you that there is still pressure there.... If you continue, and if there is no vent hole (there isn't in Travis' blocks), you could be injured or killed when the reg., with bottle attached, clears the gun which still has pressure in side.... and not a small amount, but 80 cc.... enough to do a LOT of damage....I think it is therefore safer to have to bleed down all the air before removing the bottle.... Yes, you could install an on-off valve between the reg. and drop down, so that you could remove the bottle (with reg. and valve) while filled, but you still have to bleed all the air from the gun before unscrewing the on-off from the drop down....Bob
Quote from: buldawg76 on January 09, 2017, 04:04:05 PMQuote from: rsterne on January 09, 2017, 12:29:44 PMYou wouldn't want to use 4500 psi in the tube,, but with a regulator between you are probably OK.... It's too bad we can't get burst discs at around 3800 psi, but they jump from 3K to 5K.... although from England you can sometimes get 4.5K ones.... It you had a regulator failure on a full, 4500 psi bottle, you could end up with that in the main tube.... The safety margin is probably high enough to not cause you injury, but you should degas and disassemble the gun and replace the valve mounting screws as they will have been overstressed.... I don't know what the limit if for pressure on a MRod setup, it's almost impossible to calculate the failure point of the valve screws (which is likely the weakest point) because the heads of the screws are supposed to be in shear, not the shank.... I don't know of anyone who has tested an MRod tube, with valve and fill fitting, to failure, perhaps Lloyd will do that now that he has his new 30,000 psi test rig built.... I think Lloyd uses up to 3500, and I'm pretty sure Travis uses a 250 bar tank unregulated on the FLEX.... so maybe they will chime in....BobBobI had not thought about the 4500 psi with a reg that fails sending the full pressure into the tube so you make a very good point indeed. I was planning on using the ninja style reg in the bottle so I would have the largest plenum space to obtain the best power versus volume available. Yea it would be real good if they had burst discs at even 4000k but 3800k would be better so I may look into trying to find one closer to the safety limit of the tubes rating. I know the bottle I bought from Travis when I got the full kit he stated it was safe to fill to 3500 psi so if I did use a higher PSI bottle and the reg failed I would definitely replace at a minimum the valve screws and any other piece that looks marginable with an inspection. This is some very good info to ponder as I start my build. One thing I have thought about as well is with the check valve out of the ninja reg it will not be possible to remove the bottle from the tank block since gun will stay pressurized at al times. I was thinking of using a on/off valve in between the reg and tank block so the bottle would not have to be degassed completely for service. What are your thoughts on it use to allow service of the gun.MikeMike,Why not just use a 3K disc on the output side of your Ninja? Plenty of them around as they are used on Co2 tanks. Then if the reg fails you will not get any higher then 3K in the gun.
Quote from: rsterne on January 09, 2017, 12:29:44 PMYou wouldn't want to use 4500 psi in the tube,, but with a regulator between you are probably OK.... It's too bad we can't get burst discs at around 3800 psi, but they jump from 3K to 5K.... although from England you can sometimes get 4.5K ones.... It you had a regulator failure on a full, 4500 psi bottle, you could end up with that in the main tube.... The safety margin is probably high enough to not cause you injury, but you should degas and disassemble the gun and replace the valve mounting screws as they will have been overstressed.... I don't know what the limit if for pressure on a MRod setup, it's almost impossible to calculate the failure point of the valve screws (which is likely the weakest point) because the heads of the screws are supposed to be in shear, not the shank.... I don't know of anyone who has tested an MRod tube, with valve and fill fitting, to failure, perhaps Lloyd will do that now that he has his new 30,000 psi test rig built.... I think Lloyd uses up to 3500, and I'm pretty sure Travis uses a 250 bar tank unregulated on the FLEX.... so maybe they will chime in....BobBobI had not thought about the 4500 psi with a reg that fails sending the full pressure into the tube so you make a very good point indeed. I was planning on using the ninja style reg in the bottle so I would have the largest plenum space to obtain the best power versus volume available. Yea it would be real good if they had burst discs at even 4000k but 3800k would be better so I may look into trying to find one closer to the safety limit of the tubes rating. I know the bottle I bought from Travis when I got the full kit he stated it was safe to fill to 3500 psi so if I did use a higher PSI bottle and the reg failed I would definitely replace at a minimum the valve screws and any other piece that looks marginable with an inspection. This is some very good info to ponder as I start my build. One thing I have thought about as well is with the check valve out of the ninja reg it will not be possible to remove the bottle from the tank block since gun will stay pressurized at al times. I was thinking of using a on/off valve in between the reg and tank block so the bottle would not have to be degassed completely for service. What are your thoughts on it use to allow service of the gun.Mike
As Rob pointed out, if your setpoint is low enough, a 3K burst disc will work fine.... that is what I have installed in my regulator, because it is currently set for 2000 psi, and won't likely be set much higher, because I am using a 3000 psi tank, and there would not be enough headroom.... One of the uses of a 4500 psi tank would be to use a regulator set to 3000-3600 psi, in order to be able to take advantage of the Cothran valve in a much higher powered setup.... That was why I was saying it would be nice if we could get a 3800 psi burst disc.... One more thought.... are the ON-OFF valves made for CO2 pressures, or are they intended and safe at 3000 psi (or 4500?).... Bob
Mike, the 250 and 300 bar CF bottles, and the 250 bar aluminum one I have from England, are all 18mm x 1.5mm thread, which is larger than the Ninja regs, not smaller, they are 5/8"-18 NF.... You can get an adapter from Travis for the Metric bottles, and as Rob says, you can get Metric thread regs from China and then put Ninja guts in them.... Fortunately, all the regs. are the same on the output side, 1/2"-14 NPS.... I don't know if you remember, but I recently tested a Cothran valve in my Disco Double, with a .25 cal barrel, starting at 1900 psi in this thread.... http://www.gatewaytoairguns.org/GTA/index.php?topic=117089.40 .... If you check out Reply #49, you will see a chart of velocities at various pressures with the 34 gr. JSB Heavies, and also the 50.6 gr. BBTs.... With the 34 gr., it only took 1700 psi to get 958 fps at 1.04 FPE/CI.... That was with a 25" barrel and bore-size porting to match the 1/4" exhaust port on the Cothran valve.... There is no reason the MRod Cothran won't perform the same, at the same pressure, so your only variables should be barrel length and port size.... Using the same efficiency, and a 500 cc, 3000 psi tank, you should get about 40 shots at 70 FPE.... With a 4500 psi tank, regulated at the same 1700 psi, that would more than double.... How long is your .25 cal barrel?....Bob
Quote from: buldawg76 on January 10, 2017, 02:13:26 AMBob and RobI am aware the threads on the ninja regs are 5/8-18 NF but did not know the 250 and 300 bar bottles are the bigger metric thread of 18mmX 1.5mm so to use the 250 or 300 bottles I would have to swap the guts from the ninja regs into the metric regs for them to work. I can do that if the guts are the same since I have a metric 3000 psi bottle that I just ordered a Chinese reg for to be able use it. I have also seen the CF bottles from china and was curious if they are a safe quality bottles that both of you would recommend to use for a lighter weight replacement for an aluminum bottle. The prices are much more reasonable than ones you buy here and suspect the one here may be from china as well but not sure so want to be sure they are safe since they show to be certified for build quality.Bob I did follow your cothran disco build and is partly what I am basing my goal from the Brod on but was going to go back and read thru to refresh me on the reg pressure and other aspects that I will need to use to build the Brod. I am using a MM 20 inch hammer forged barrel in the build so its 5 inches shorter than your disco and was going to use a .1875 TP port out of the cothran valve all the way into the barrel. So I may have to raise the reg set pressure closer to 2000 psi to make up for the smaller Port. I will be happy with 40 shots per fill but doubling that would be even better. Lots of things to think about and test to get the best overall efficiency and power. MikeFrom all of my research (internet and hands-on) the 3K and 4500 reg differ only in the lettering on them. All of the internal parts seem to function exactly the same when interchanged. Did you also get a Ninja piston kit to use with the 3K bottle? If not just ask Travis about the differences. I think you find the $14 well spent. About the CF bottles - just make sure which ever one you get it is DOT approved, otherwise no Hydro Testing facility will certify them......at least none I have talked to.
Bob and RobI am aware the threads on the ninja regs are 5/8-18 NF but did not know the 250 and 300 bar bottles are the bigger metric thread of 18mmX 1.5mm so to use the 250 or 300 bottles I would have to swap the guts from the ninja regs into the metric regs for them to work. I can do that if the guts are the same since I have a metric 3000 psi bottle that I just ordered a Chinese reg for to be able use it. I have also seen the CF bottles from china and was curious if they are a safe quality bottles that both of you would recommend to use for a lighter weight replacement for an aluminum bottle. The prices are much more reasonable than ones you buy here and suspect the one here may be from china as well but not sure so want to be sure they are safe since they show to be certified for build quality.Bob I did follow your cothran disco build and is partly what I am basing my goal from the Brod on but was going to go back and read thru to refresh me on the reg pressure and other aspects that I will need to use to build the Brod. I am using a MM 20 inch hammer forged barrel in the build so its 5 inches shorter than your disco and was going to use a .1875 TP port out of the cothran valve all the way into the barrel. So I may have to raise the reg set pressure closer to 2000 psi to make up for the smaller Port. I will be happy with 40 shots per fill but doubling that would be even better. Lots of things to think about and test to get the best overall efficiency and power. Mike
^X2, good advice, Rob, particularly on making sure your CF bottle is DOT approved.... BTW, Travis sells 250 bar, 500 cc DOT Approved CF Bottles, as used on the FLEX.... I just set up Lloyd's spreadsheet using the numbers from my .25 cal DD with the Cothran valve, to see what your changes might do to the required setpoint pressure.... My setup gave 958 fps @ 1700 psi with a 135 cc plenum and a 25" barrel, with 34 gr. JSBs.... Changing from my 135 cc plenum down to 80 cc should drop the velocity at 1700 psi to 946 fps.... which would only require a 50 psi increase to compensate (1750 psi)....Changing from a 25" barrel to 20" should drop the velocity at 1700 psi to 913 fps.... and would require an increase to 1900 psi to get back to 962 fps....The two changes together should give you 951 fps @ 1900 psi.... assuming the MRod and Disco Cothran valve perform equally (they should)....Lloyd's spreadsheet isn't designed to look after altering port sizes (that's coming).... but I have a rough correction that I apply.... When I do that, starting with the 80cc plenum and 20" barrel at 1700 psi.... changing from 1/4", bore-size porting down to 3/16" could drop the velocity to 871 fps @ 1900 psi.... and require an increase to 2300 psi to get back to 951 fps....From those calculations, the plenum you can almost ignore, and you can compensate for the 20" barrel without too much problem.... but the "small" ports will really cost you in performance.... These are just predictions, but you might have a look at using larger ports to flow enough air for the 34 gr. pellets without having to use a setpoint over 2000 psi....Bob
If you read through the DD Powerhouse valve thread, is gives the barrel port dimensions to equal 1/4" diameter exhaust and transfer ports.... IIRC, it was 3/16" wide by 5/16" long.... I used a 3/8" OD transfer port to match up with the Cothran valve, so you have to drill the tube and receiver to match that, and mill a 3/8" flat on the barrel (minimum depth).... I used a piece of 3/8" OD Teflon rod, drilled with a size "F" drill (0.257") for the TP, to match the Cothran exhaust port.... The transition from round to oblong was made within the barrel wall itself.... Bob
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