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Author Topic: Regulated Disco Double  (Read 5759 times)

rsterne

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Regulated Disco Double
« on: November 20, 2016, 12:42:31 PM »
Over a year ago, I suggested to Lloyd Sikes at the AirGun Lab, developer of the Disco Double, that he might consider making a regulator cartridge that could be installed inside the front upper plug that he supplies with his DD kits.... He thought it was a good idea, but life got in the way, so we didn't get around to doing the drawings until this Spring, and Lloyd made a prototype which exceeded our expectations.... He has since had some CNC'd, and has them in stock.... In addition, he has made an agreement with Eric Kuehn of Stalwart Arms to assemble and market the Disco Double kits.... I'll let Eric and Lloyd answer your questions about prices and availability (through PMs, please), the purpose of this thread is to build a Regulated Disco Double, and put the new regulator through it's paces.... Lloyd graciously supplied me with a regulated DD kit, and I purchased the rest of the parts shown in the photo below towards this project....



Starting at the top, the barrel is a .22 cal TJ's with a 1/2" OD, that Sean Pero and I designed a couple of years ago.... I have had it sitting on the shelf, awaiting a suitable project, and now is the time.... It is 0.217" land, 0.213" groove, with a 16" twist.... I have two projectiles in mind, both recent developments.... One is the new 34 gr. JSB Beast pellet, and the other is the recently released NOE .217 cal 30 gr. Bob's Boattail, which I designed to work in this barrel.... My mould is in the mail as I write this, and it has a Lyman HP pin in one cavity which will drop the weight a couple of grains.... Both of these will fit and function in a PRod magazine, and I will be building my own breech to hold that and the shrouded barrel.... The lightest pellet I plan on using is the 25 gr. JSB Monster, although I know that the 18 gr. Heavies are deadly in this barrel, as are the 16 gr. Exacts and Polymag Predators....

The next item down is a Discovery main tube from Crosman.... I will be drilling out the transfer port hole to accept a larger, 5/16" OD TP, and deburring it, plus drilling a tiny vent hole 9/16" from the front on the bottom, otherwise I plan no modifications to it.... The O-rings are part of the DD kit, which is below the main tube.... Not shown are the hammer and SSG, which have yet to be made.... I also plan on using a Carbon Fibre tube as a shroud, which will place the barrel in tension to stiffen it.... The tension will be adjustable using my Belleville washer setup at the muzzle.... and of course the associated parts have yet to be machined....

The regulated Disco Double tube kit arrived assembled, just as you see it in the photo above.... It consists of the same 120 cc reservoir used in the DD kit, good for at least 3000 psi safe working pressure.... At first glance, it appears almost identical to the original unregulated DD kit, I'll get to the differences in a minute.... To the right of the DD kit are a PRod gauge block, and a much modified Disco valve which I have already written about in an earlier thread.... In addition to bore-size porting throughout (0.219" exhaust port, 0.266" throat with MRod poppet).... the valve is fitted with high-tensile 10-32 screws allowing a MSWP of over 3000 psi....

Below the DD kit are a pair of barrel bands I got from Lloyd with the DD kit.... There are a variety available, these are for use with a BNM breech fitted with a 1" shroud.... I will be using a 7/8" CF shroud on my gun, so I will have to fit them with a larger cross-section O-ring to hold snugly on the smaller shroud.... To the right of those are a PRod trigger group and typical Crosman skeleton stock.... I will eventually modify the LoP and cheek rise on that to fit me....

Now to the important part, the new AirGun Lab Regulator.... It is a cartridge design, using thick 1/2" OD Bellevilles, with the piston retained in the rear of the upper plug (inside the upper tube) with a snap-ring as shown.... The air enters the upper reservoir through the hole in the center of the piston, which is threaded 6-32 for easy removal of the piston....



Looking at the front of the regulator, under the upper plastic cap, you will see an adjustment screw.... This allows moving the floating seat fore and aft, which allows you to externally adjust the setpoint pressure.... This is an exceptional feature, and part of our design criteria.... It was made possible by the position of the regulator at the front end of the upper tube, which now becomes the plenum.... a very large one at 135 cc.... The air pressure in the gun should be reduced below the current (or intended) setpoint (whichever is lower), so that the regulator piston is "open" and no pressure is on the seat before changing the adjustment, to avoid damaging the (replaceable) HP seal on the end of the piston.... IIRC, the adjustment range is about 500-2500 psi, Lloyd please correct me if I have that wrong....  :-[ .... The two protective caps, one for the adjustment screw and the other to cover the built in male Foster fill fitting, are identical, and interchangeable.... You can see them in place in the first photo....



The side view, below, shows that the new upper plug is a bit longer than the previous (unregulated) version, to allow room for the regulator piston.... Note that there are two O-ring grooves, but only one O-ring.... The reference vent for the center (spring) portion of the regulator is between those two O-ring grooves, on the lower side, hidden by the bottom tube.... When the regulator is in place, the O-ring is placed in the aft groove (as shown), and the venting occurs towards the front, through the hole I will drill in the main tube, just inboard of the threads.... If you want to run the gun without the regulator, you simply remove the regulator cartridge, and move the O-ring to the front groove.... The vent hole in the regulator is now behind the O-ring, which prevents venting.... This is an elegant and simple way to allow removal of the regulator without having to replace the upper tube.... because the vent hole in the tube is inboard of the threads, but outboard of where the O-ring seals.... Again, this shows the attention to detail that occurred with the synergy that Lloyd and I have when working on projects like this.... I take great pleasure in working with him because of that....



Anyway, there is the starting point for this exciting new project, and the details on the new AirGun Lab regulator for the Disco Double kits.... In addition to it being an option on the new DD kits (they all now share the new upper plug that accepts the regulator cartridge).... they are also available as a retrofit for the previous DD kits which were unregulated.... All you need is the new upper plug with regulator, shorten the hollow connecting bolt a bit (to miss the adjusting screw) and drill the vent hole in your main tube, and you're good to go.... You could even reinstall the original DD upper plug, or go back to a Crosman fill fitting, and the vent hole in the tube isn't an issue because of it's location.... This means complete interchangeability of parts, with no obsolescence, again one of our design criteria.... I'm looking forward to getting started on my new Regulated Disco Double....

Bob




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Rdsail

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Re: Regulated Disco Double
« Reply #1 on: November 20, 2016, 03:10:07 PM »
very cool! I talked to Lloyd a while back and he mentioned that he was working on this Disco regulator that can be externally adjusted. Makes me thick about building one.



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Re: Regulated Disco Double
« Reply #2 on: November 20, 2016, 05:50:47 PM »
If I see this right ?  ... upper tube is HP and lower containing REG on the end is a LP tube ?
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Scott

rsterne

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Re: Regulated Disco Double
« Reply #3 on: November 20, 2016, 06:45:14 PM »
Nope, other way around.... The lower tube (with the Foster) is the HP reservoir, and the upper tube (the original Disco main tube) has the regulator in the front of it and serves as the plenum.... The valve is in the upper tube, as per usual....

Bob
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Re: Regulated Disco Double
« Reply #4 on: November 20, 2016, 08:54:52 PM »
Nope, other way around.... The lower tube (with the Foster) is the HP reservoir, and the upper tube (the original Disco main tube) has the regulator in the front of it and serves as the plenum.... The valve is in the upper tube, as per usual....

Bob

LOL ... down side up orientation, forgot about that  :o

That said ... so you have the main tube w/ valve being essentially one big plenum running at regulated pressure ?
Good way to get a very stable shot to shot velocity so long as HP storage feeding it is above Regs set pressure.
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rsterne

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Re: Regulated Disco Double
« Reply #5 on: November 21, 2016, 09:06:24 AM »
That is correct.... The plenum is huge, big enough to handle pretty much anything that would be realistic with a Disco.... I did a calculation in another thread that showed that using this setup for a .35 cal pellet shooter, with a Cothran valve, and the regulator set to 2000 psi.... should give 5 equal shots at 135 FPE with 78 gr. JSBs.... I know of no other setup for a Disco (other than a bottle) that could do that....

Just to give an idea, a stock Disco reservoir is 135 cc, and the Disco Double lower tube is about 120.... If you set the regulator to 1500 psi, and fill the lower tube to 3000 psi, the equivalent total volume at 1500 psi is 375 cc.... Without the lower tube, if you installed a regulator in the upper tube that resulted in a 100 cc HP reservoir and a 15 cc plenum, and then filled the upper tube to 3000 psi, you would have the equivalent of 215 cc.... If you only used the stock 2000 psi, that would be only 148 cc available at 1500 psi....

Bob
« Last Edit: November 21, 2016, 09:08:13 AM by rsterne »
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grumpy

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Re: Regulated Disco Double
« Reply #6 on: November 21, 2016, 11:19:05 AM »
I am glad to see Lloyd suggested this.
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rsterne

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Re: Regulated Disco Double
« Reply #7 on: November 21, 2016, 02:32:34 PM »
Don't quite understand, Dave, but whatever....  ???

Today I drilled out the transfer port hole in the Disco tube to 5/16", and while I had it mounted in the mill I lengthened the front of the cocking slot for the hammer by 0.20".... I will be increasing the hammer stroke, and just wanted to make sure the cocking pin won't hit the end of the slot on firing.... I then deburred all the slots and holes, paying particular attention to the gauge hole, which makes a great cheese grater the way Crosman machine it, but not very kindly to the O-rings you have to slide past it.... I pay particular attention to the front and especially the back inside edge, rounding it so that the O-rings can slide past it without getting torn.... Not doing that the first time you have a Disco apart is a big mistake.... I then carefully cleaned the inside of the main tube....

I mentioned before that the bands I got from Lloyd that hold the tubes together were for a BNM breech with 1" shroud.... The upper portion has an O-ring groove machined into it for a #022 O-ring, that will hold that diameter shroud.... I will be using only a 7/8" OD shroud, but I found that by using #212 O-rings I could used the same bands, as they have the same OD but the smaller ID I require.... However, the groove in the bands was too narrow, so I chucked them I my lathe and put a taper on the side of each groove so that they were 0.140" wide at the inside, in sort of a half-hexagon shape.... I did NOT have to cut the groove any deeper, just wider at the inner edge.... With a 70D O-ring installed, they fit the 7/8" tubing I have nicely, a snug, sliding fit with the O-ring compressed about 0.010".... This will hold the shroud well, without being rigid.... and there is no way the O-ring can pop out once the tube in installed....

I checked the fit of the valve, ground a notch in the top rear to miss the forward breech screw location, and also ground a notch in the bottom rear to allow better venting of the space between the hammer and valve through the hole behind the bottom screw.... I then  disassembled and carefully cleaned the valve, lubed the stem and O-ring and put it back together.... I then lubed the valve and gauge block O-rings, slid the valve into place, installed the 10-32 screws, then installed the gauge port and a 3000 psi gauge.... As the O-rings pass the gauge hole, be VERY careful they don't get cut.... I use my fingernail, or a small flat-bladed screwdriver, to coax them past my nicely rounded edge, but you still need to be careful and work slowly.... I rolled a #016 O-ring onto the upper plug of the Disco Double kit, where it butts against the end of the main tube, lubed the O-ring that seals inside the tube, and screwed the tube onto the upper DD plug that contains the regulator.... Just before it contacts the O-ring, have a look at where the gauge is in relation to the lower DD tube, and stop threading it on when the gauge lines up with the lower tube and the O-ring is under the least compression possible.... Its only purpose is to fill the gap between the end of the upper tube and the upper plug for appearance and to keep the dirt out.... There is plenty of thread engagement without cranking it that last turn and squeezing the O-ring out of the groove....

I then temporarily installed the trigger group so that I could align the position of the lower tube with it.... I slid the narrow tube band (the one without the Picatinny rail) onto the two tubes, right back to the end of the lower tube, leaving only the flange on the aluminum plug past the band.... Once I was happy with the alignment of the tubes I snugged the setscrews on the bottom of it, turned the assembly around and viewing from the front made sure the tubes weren't twisted and sat parallel with each other.... I then tightened the setscrews in the tube band, being careful not to tighten them so much they would crush the tube, which is thin there because that is where it is threaded.... This completed the pressure assembly, and it now looks like this....



At this point, it was ready for a leak test.... I slowly put in 1000 psi, and checked for leaks with soapy water on a small brush.... Finding none, I the gradually filled the reservoir, 200 psi at a time, allowing for the pressure to equalize and kept my eye on the gauge, which reads the pressure downstream of the regulator, so it will tell you the setpoint.... It stopped and held at 1600 psi, so I stopped filling at 2000 psi, waited a few minutes to be sure it hadn't crept up (it hadn't budged), and since I was still attached to my Great White I bled the line very slowly, which will often leave the check valve in the Foster open and allow you to bleed air from the bottom tube.... It worked, and once I got the tube down to 1400 psi I checked the gauge on the gun, and it still read 1600 (as it should).... I then quickly bled the air from the line to my tank, leaving 1400 psi in the lower tube and 1600 in the upper.... I wanted to increase the setpoint of the regulator, both because I expected to need a bit more pressure for this project, and because I wanted to play with the adjustment.... That meant that I had to bring the pressure in the upper tube down to less than the current setpoint, so I didn't damage the HP seat in the regulator....

The only way to do this, or at least the easiest way, was to fire the gun, so I temporarily installed the trigger group, a hammer, spring, and RVA, and making sure the transfer port was facing away from me, pulled the trigger.... I wish I had rembered to remove my hearing aids and put in my ear plugs, because it was LOUD!.... Fortunately, my hearing aids have a "clamping circuit" that prevents loud noises from getting through, so the actually act like (rather noisy) ear plugs.... Just the one shot dropped the pressure to 1400 psi, so now both tubes were below the current setpoint.... Since I was going to increase the setpoint, I didn't need to remove any more air.... If I had been going to lower it, then the pressure in both tubes would have to be lowered BELOW the new setpoint to make sure you don't damage the HP seat.... To increase the pressure you have to move the seat OUT, towards the front of the gun.... This allows the piston to move further before closing the HP seat, which compresses the Belleville springs further.... That takes more force, which means more pressure, and you end up with a higher setpoint.... To lower the pressure you need to do the opposite, you need to move the seat IN.... If you didn't bleed air from the gun, then you would be screwing the adjustable metal seat into the plastic seat on the end of the piston, and could easily damage it.... To repeat....

Adjuster OUT (CCW) increases the setpoint pressure....  Adjuster IN (CW) decreases the setpoint pressure....

If the screw is hard to turn, you probably forgot to bleed the pressure down, STOP and make sure both tubes are BELOW the lowest pressure setpoint you need.... The slot in my adjuster, viewed from the front, was at about a 45* angle, from 10:30 to 4:30 o-clock.... I decided to try 1/8 turn CCW, so I set the slot horizontal, at 9:00 to 3:00 o'clock.... The screw moved with noticeable drag from the O-rings that seal it, but was not difficult to adjust.... I then reconnected the Foster to my Great White and added 200 psi at a time, watching the pressure gauge to see how much I moved the setpoint.... It was almost exactly 200 psi, it now settled in and stayed at 1800, which is pretty close to where I think I need it.... certainly close enough for initial trials.... I continued filling the lower tube to 3000 psi.... let it sit for a while to cool, and topped it up before coming in to take the photo and write this post.... The assembly will sit under pressure while I continue to work on other parts of the gun as a leak test.... Note that if the gauge eventually shows a pressure drop, if would indicate that the leak is downstream of the regulator.... If there was a leak upstream of the regulator, the gauge (in theory) would not give you an indication of that.... However, the next time you went to fill from a tank, you could hear the check valve in the Foster click below the pressure you left the gun at....

Bob
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Re: Regulated Disco Double
« Reply #8 on: November 21, 2016, 03:39:44 PM »
Sorry Bob, sorta got cut off in my post. What I meant is Lloyd was telling me how well my efficient my .257 Brod is shooting with the Cotrane valve an his regulator. Thought he mentioned to me when we last spoke that he was going to suggest regulating your Disco to help its efficiency.
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rsterne

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Re: Regulated Disco Double
« Reply #9 on: November 21, 2016, 06:40:12 PM »
Ahhhhhhh, now I understand.... Lloyd and I have been working together on this regulator for "well over a year" according to him....  ::) .... I was actually the one who first suggested it.... We are both working on Cothran valves, his in an MRod (yours?) and mine in a Disco Double, but not this one, this will have one of my valves, as it's only .22 cal and I can get full bore-area ports no problem, have done it many times....

No idea if the way the guns are being configured is the way they are going to stay, of course.... I may end up swapping parts around at some point.... That's the nice thing about Crosman LEGO airguns, lots of interchangeablity....  8)

Bob
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Re: Regulated Disco Double
« Reply #10 on: November 21, 2016, 07:13:03 PM »
I'm sorry, did not mean to imply anyone took an idea from another. Thought maybe Lloyd shared the sucess of the reg in mine to help you. Now the Coltrane valve is a semi new add on to mine. He liked it with the regulator better then his own valve design.

Dave
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rsterne

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Re: Regulated Disco Double
« Reply #11 on: November 21, 2016, 08:03:39 PM »
It's all good, Lloyd and I share back and forth all the time....  8)

Bob
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rsterne

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Re: Regulated Disco Double
« Reply #12 on: November 22, 2016, 06:16:32 PM »
Since I am using a PRod pistol grip trigger group and skeleton buttstock, I needed a forearm of some kind.... I ordered a pair of tube bands from Lloyd with the thoughts that I could probably come up with a way to mount a slotted piece of black 1-1/4" ABS Pipe between them to serve that purpose.... Here is the adapter I made, shown next to a tube band....



It is made from a piece of 1-3/8" bar stock, drilled out to 1" and then bored out to 1.096" to the same depth as the tube band.... I then machined away two 90* segments, leaving the other two to fit around the lowest portion of the band.... This will mount the tubing concentric with the lower tube, as it is 1-3/8" ID so will just slide over the adapter.... I had to machine away the top portion to miss the upper tube (the Disco main tube), and the ABS pipe will have to be slotted to miss that tube as well.... Here are the two adapters, slid onto the tube bands, and sitting in the appropriate locations on the double tube assembly.... The front one can be positioned anywhere I want, depending on the length forestock I choose....



As you can see, the adapters are on the inside of the tube bands, and the split piece of pipe will simply slide over them.... I can extend the pipe towards the rear, closer to the gauge if desired, as the setscrew portion of the rear band is below the diameter of the adapter.... I had to just file the corners slightly to prevent them dragging on the ID of the pipe.... On the front, you can see the Picatinny mount which is part of the front tube band.... I projects high enough above the adapter to clear any standard Weaver mount or ring, but I may have to notch the front of the tube a bit to clear the BiPod mount I have, it's a bit wider than the tube band on both sides....

This is going to work perfectly.... I will drill both sides of each adapter and tap the tube band for small screws, and also drill the sides of the plastic pipe and tap the adapters so that everything is rigid when assembled.... That, and cutting a wide slot in the pipe, are all that remain to complete the forestock....

Bob

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Christopher

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Re: Regulated Disco Double
« Reply #13 on: November 23, 2016, 02:20:46 AM »
Looking good Bob.

Chris
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rsterne

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Re: Regulated Disco Double
« Reply #14 on: November 23, 2016, 06:24:06 PM »
I completed the Forestock today.... The stock itself is a foot of 1-1/4" ABS pipe with a slot cut in the top to clear the main tube.... It is mounted with four 6-32 pan head screws tapped into the adaptors I made yesterday, which are secured to the tube bands I got with a pair of 6-32 setscrews each.... Here is what the assembly looks like.... I slid a shroud I borrowed from my other Disco Double into place just to see what it looks like....



As you can see, the Picatinny mount protrudes below the stock at the front, and it can be used for any accessory, such as a flashlight, laser, or a BiPod.... I fitted the PRod trigger group and the Skeleton stock, along with a BiPod for the photo below.... There is no breech on the gun, but it gives you an idea of what it will look like when finished....



I used a holesaw to cut a circular hole in the bottom rear of the stock and then tapered the sides for appearance.... In profile view the stock hides the gauge, but it is easily readable from the bottom, as in the photo below....



The forestock is in a great location, and is long enough for shooting offhand or prone, and the BiPod is in an ideal location, it can be folded forward, and remains within the overall length, even if the legs are extended.... I'm very pleased with the overall proportions and appearance, and although it doesn't yet have a breech or barrel, it's shaping up to be extremely light and well balanced....

Bob
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