GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: antithesis on July 07, 2021, 04:36:30 PM
-
I've decided to start working on another 392 and I have many of the basic principles of improving multi pump performance in memory, I have intentions on keeping this one RELATIVELY simple.
The main things I'm considering is:
1. The standard 392 valve air capacity is ?
2. The ideal valve capacity (pumping effort not withstanding) for this is supposed to be roughly half the bore volume...(?) Correct me if I'm wrong ...
3. I'm keeping the standard cup and cone interface (no flat topping). I have the adjustable length pump rod, I am looking at reducing headspace as much as possible.
Can shimming the outer rim of the cup help with this, pushing the final air from the outside in at the end of the stroke? Is there any way to improve the standard interface making it more efficient?
I was considering something specific here. I was going to close more dead space by making a pin that goes from the Cone tip and mounting into the check valve face, removing the little bit of dead space in the valve inlet. If anyone has tried similar or thinks it a good or bad idea I want input on this one...
4. The cartridge valve 3 oring mod that reduces the infamous space between valve and pump tube, has this been found effective in any capacity and if so what benefit have you seen?
5. Is there really anything to gain by porting out any of the components or reducing stem diameter? At least would it be detrimental?
I know a lot of guys who have done pretty cool performance mods and I'm sure I can do better than 15 ftlbs. I have before.
If there is anything else to add I'll be listening
-
I'd like to follow this thread......
-
I'd like to follow this thread......
Follow away my friend. Just hopefully someone will come along with their experiences and /or theories, or it could get boring fast. I am keeping this an open sight rifle too for the time being and my look at improving the current blade and leaf, as I get a somewhat hazy sight picture on the stock sight. Maybe exposing the brass on the edge of the front blade? I dunno yet. But I am really tempted to try to make a peep rear
-
Psipumper (Charles) stated that the third o-ring was good for 12 fps at 8 pumps (https://www.gatewaytoairguns.org/GTA/index.php?topic=180192.msg156063564#msg156063564 (https://www.gatewaytoairguns.org/GTA/index.php?topic=180192.msg156063564#msg156063564)).
I ground a discovery stem down to 1/8" and I was happy with the results in combination with other changes. If my memory serves. The throat to valve stem clearance was the smallest area in the valve / transfer port / bolt probe flow passage.
-
1. Standard 39X valve volume is about 4.2 cc.... That is about 35% of the volume of a 392 barrel....
2. MAXIMUM practical valve volume for a "pump and dump" pumper is half the bore volume.... Beyond that you will be wasting a HUGE amount of air.... Most pumpers have a valve that is 1/4 to 1/3 of the bore volume.... If you want to build an "Air Conserving Pumper" (ACP) where you leave air in the valve after the shot to increase efficiency, a larger valve is great, but be prepared to pump a LOT more....
3. Matching the profile of the cup to the valve can reduce deadspace.... adjusting the pump rod length is also great....
4. The third O-ring can help....
5. Porting can help....
Here is my build thread.... https://www.gatewaytoairguns.org/GTA/index.php?topic=166668.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=166668.0)
Bob
-
I dug into my notes/posts and found the following measured diameters:
Valve throat 0.221"
Exhaust valve stem 5/32 (0.156")
Valve port 0.164ish"
Barrel port 5/32 (0.156") (complete with sharp edges)
Bolt probe 1/8 (0.125")
Leade 0.22ish"
So the throat is the smallest passage and grinding the stem down to 1/8 (0.125") in this area resolves that. The barrel port is the second smallest passage and it can then be increased slightly without creating loading issues. Of course blending of transitions and angling ports is helpful too.
-
Disassemble the pump rod, get or make a steel washer .060-.080 thick and the same diameter as the bottom of the pump cup holder. Braze the washer to the bottom of the pump cup holder and piston rod. Under pressure the pump cup holder flexes backward on the pump rod enough that all the air is not pushed into the valve. This mod. will increase the pressure in the valve.
-
Disassemble the pump rod, get or make a steel washer .060-.080 thick and the same diameter as the bottom of the pump cup holder. Braze the washer to the bottom of the pump cup holder and piston rod. Under pressure the pump cup holder flexes backward on the pump rod enough that all the air is not pushed into the valve. This mod. will increase the pressure in the valve.
Actually I have the Mac1 adjustable rod and i also centered a piece of pultruded CF tube around the rod and will shim it as per necessary. Should achieve the same effect.
I am using alot of parts from a previous unfinished 392 project and have some upgraded parts available, I had planned originally to attempt a small reservoir to make a multi shot pumper but I'm going to keep this one simple.
I do remember your 392 project Bob and thanks for the link I'll be looking closely at your conclusions. I already have a reinforced front end to take more punishment as well as (I believe) 3/16 pins all around.
Did the disco poppet hold well at low pressure? I've got enough tubing to bush the stem hole as long as it's long enough to work, I'm pretty sure I have a few of them I was going to try for the first project.
So (particularly Bob) do any of you think that filling the dead space between the tip of the cone and the check face would work to my benefit? It seems to me that is a large part of the objective of flat topping is that flattening the valve face reduces that little tunnel between the tip and the check poppet face.
Good info guys keep it coming if you have any more. So far I see that the stem diameter needs reduced and the air inlet to the barrel needs opened up slightly. It doesn't look like the 3rd oring mod is enough to be worth doing, although if I can cut a 3rd groove I will.
I'll also keep the valve volume where it is as I dont think I'd need any more for single shot work. If I can close enough headspace I might even reduce it a little.
-
The disco exhaust valve sealed up fine for me. I did lap it to the seat with some JB bore paste. I had feared sealing issues with it but it has proven capable of holding one or two pumps indefinitely. The nice thing is that it shares a stem diameter with the 392 part, so it drops in without modifying the valve and it is easy enough to take it down to 1/8" in the throat area.
If you wish to keep the valve volume roughly the same (I actually decreased mine), then you can turn some of the diameter down to decrease the preload on the check valve. It has the same affect as shortening the check valve but without increasing the valve volume as much.
-
The disco exhaust valve sealed up fine for me. I did lap it to the seat with some JB bore paste. I had feared sealing issues with it but it has proven capable of holding one or two pumps indefinitely. The nice thing is that it shares a stem diameter with the 392 part, so it drops in without modifying the valve and it is easy enough to take it down to 1/8" in the throat area.
If you wish to keep the valve volume roughly the same (I actually decreased mine), then you can turn some of the diameter down to decrease the preload on the check valve. It has the same affect as shortening the check valve but without increasing the valve volume as much.
That was exactly another thing I was going to do, I am thinking for my purposes a slightly smaller valve volume would be ideal. If only I can figure out how to install a gauge into it to keep precise track of pressures.
-
The disco exhaust valve sealed up fine for me. I did lap it to the seat with some JB bore paste. I had feared sealing issues with it but it has proven capable of holding one or two pumps indefinitely. The nice thing is that it shares a stem diameter with the 392 part, so it drops in without modifying the valve and it is easy enough to take it down to 1/8" in the throat area.
If you wish to keep the valve volume roughly the same (I actually decreased mine), then you can turn some of the diameter down to decrease the preload on the check valve. It has the same affect as shortening the check valve but without increasing the valve volume as much.
That was exactly another thing I was going to do, I am thinking for my purposes a slightly smaller valve volume would be ideal. If only I can figure out how to install a gauge into it to keep precise track of pressures.
Agreed. Mine shoots wadcutters at 525fps on just three pumps - that is the advantage to going smaller on volume.
I wouldn't discount the third oring if you have a means to do it. Percentage-wise it is a significant gain.
-
The disco exhaust valve sealed up fine for me. I did lap it to the seat with some JB bore paste. I had feared sealing issues with it but it has proven capable of holding one or two pumps indefinitely. The nice thing is that it shares a stem diameter with the 392 part, so it drops in without modifying the valve and it is easy enough to take it down to 1/8" in the throat area.
If you wish to keep the valve volume roughly the same (I actually decreased mine), then you can turn some of the diameter down to decrease the preload on the check valve. It has the same affect as shortening the check valve but without increasing the valve volume as much.
And what's up with the brass at the spring end of the check piece? The how and the why if you can
-
The disco exhaust valve sealed up fine for me. I did lap it to the seat with some JB bore paste. I had feared sealing issues with it but it has proven capable of holding one or two pumps indefinitely. The nice thing is that it shares a stem diameter with the 392 part, so it drops in without modifying the valve and it is easy enough to take it down to 1/8" in the throat area.
If you wish to keep the valve volume roughly the same (I actually decreased mine), then you can turn some of the diameter down to decrease the preload on the check valve. It has the same affect as shortening the check valve but without increasing the valve volume as much.
And what's up with the brass at the spring end of the check piece? The how and the why if you can
It is a #6x1" screw that I used to join two check valves together. Post #22 from the following thread... https://www.gatewaytoairguns.org/GTA/index.php?topic=180192.msg156063564#msg156063564 (https://www.gatewaytoairguns.org/GTA/index.php?topic=180192.msg156063564#msg156063564)
-
The disco exhaust valve sealed up fine for me. I did lap it to the seat with some JB bore paste. I had feared sealing issues with it but it has proven capable of holding one or two pumps indefinitely. The nice thing is that it shares a stem diameter with the 392 part, so it drops in without modifying the valve and it is easy enough to take it down to 1/8" in the throat area.
If you wish to keep the valve volume roughly the same (I actually decreased mine), then you can turn some of the diameter down to decrease the preload on the check valve. It has the same affect as shortening the check valve but without increasing the valve volume as much.
And what's up with the brass at the spring end of the check piece? The how and the why if you can
It is a #6x1" screw that I used to join two check valves together. Post #22 from the following thread... https://www.gatewaytoairguns.org/GTA/index.php?topic=180192.msg156063564#msg156063564 (https://www.gatewaytoairguns.org/GTA/index.php?topic=180192.msg156063564#msg156063564)
Was that a method of reducing volume?
And I guess I am going to just go ahead and mount a pin into the check face....at the worst i
I dont think it's going to hurt anything. But I understand that at higher pressures every little bit of dead space counts
-
The disco exhaust valve sealed up fine for me. I did lap it to the seat with some JB bore paste. I had feared sealing issues with it but it has proven capable of holding one or two pumps indefinitely. The nice thing is that it shares a stem diameter with the 392 part, so it drops in without modifying the valve and it is easy enough to take it down to 1/8" in the throat area.
If you wish to keep the valve volume roughly the same (I actually decreased mine), then you can turn some of the diameter down to decrease the preload on the check valve. It has the same affect as shortening the check valve but without increasing the valve volume as much.
And what's up with the brass at the spring end of the check piece? The how and the why if you can
It is a #6x1" screw that I used to join two check valves together. Post #22 from the following thread... https://www.gatewaytoairguns.org/GTA/index.php?topic=180192.msg156063564#msg156063564 (https://www.gatewaytoairguns.org/GTA/index.php?topic=180192.msg156063564#msg156063564)
Was that a method of reducing volume?
And I guess I am going to just go ahead and mount a pin into the check face....at the worst i
I dont think it's going to hurt anything. But I understand that at higher pressures every little bit of dead space counts
Yes, the additional check valve was used to decrease the valve volume by roughly 10 percent. This makes it more efficient with lower quantity of pumps.
The concerns that I would have with filling the valve inlet hole would be that it needs to be robust and that it could obstruct the flow when pumping. Otherwise, your logic about it being dead space and being harmful for pumping efficiency is valid. Another approach would be to decrease the passage diameter rather than trying to occupy some of it with a pin.
-
The disco exhaust valve sealed up fine for me. I did lap it to the seat with some JB bore paste. I had feared sealing issues with it but it has proven capable of holding one or two pumps indefinitely. The nice thing is that it shares a stem diameter with the 392 part, so it drops in without modifying the valve and it is easy enough to take it down to 1/8" in the throat area.
If you wish to keep the valve volume roughly the same (I actually decreased mine), then you can turn some of the diameter down to decrease the preload on the check valve. It has the same affect as shortening the check valve but without increasing the valve volume as much.
And what's up with the brass at the spring end of the check piece? The how and the why if you can
It is a #6x1" screw that I used to join two check valves together. Post #22 from the following thread... https://www.gatewaytoairguns.org/GTA/index.php?topic=180192.msg156063564#msg156063564 (https://www.gatewaytoairguns.org/GTA/index.php?topic=180192.msg156063564#msg156063564)
Was that a method of reducing volume?
And I guess I am going to just go ahead and mount a pin into the check face....at the worst i
I dont think it's going to hurt anything. But I understand that at higher pressures every little bit of dead space counts
Yes, the additional check valve was used to decrease the valve volume by roughly 10 percent. This makes it more efficient with lower quantity of pumps.
The concerns that I would have with filling the valve inlet hole would be that it needs to be robust and that it could obstruct the flow when pumping. Otherwise, your logic about it being dead space and being harmful for pumping efficiency is valid. Another approach would be to decrease the passage diameter rather than trying to occupy some of it with a pin.
I'd like to try to find a tightly restricted vented grub screw in maybe 6-32. I tapped another 392 valve inlet with a 6-32 screw that I slit in the middle in conjunction with a oring to make a experimental check design I didn't try. Maybe do the same but this time scallop two air slots down the length into the threads. I believe that could be another viable idea. But at least you confirmed my logic to be on the right path.
If I want to further reduce capacity what do you think could be used? I have a sheet of phosphor bronze I could roll up to reduce the ID
-
I agree with Eric on reducing the inlet hole diameter . I use a 1 mm hole and noticed no resistance in pumping. If anything the back pressure would seal the pump cup better when pumping. The first ones I pressed the sleeve in a little shy of the CV surface but have decided flush would reduce the CV pressure to open because of the smaller hole seat. Probably doesn’t amount to much but why not.
Like so many things with the 392, it takes a full machine shop to perfect unfortunately.
-
I agree with Eric on reducing the inlet hole diameter . I use a 1 mm hole and noticed no resistance in pumping. If anything the back pressure would seal the pump cup better when pumping. The first ones I pressed the sleeve in a little shy of the CV surface but have decided flush would reduce the CV pressure to open because of the smaller hole seat. Probably doesn’t amount to much but why not.
Like so many things with the 392, it takes a full machine shop to perfect unfortunately.
Yes true enough, honestly I'm happy enough to shoot it as is but if you want improvement with this one its definitely gonna be hard earned. I'll ponder what to reduce the diameter with
-
Interesting, following this thread.
Haven't worked on a 392 but made 19 FPE with a 312 on 10 pumps, 14.3 CPHPs.
Thanks in part to a Mac1 steroid pump link.
https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.msg155882349#msg155882349 (https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.msg155882349#msg155882349)
-
Interesting, following this thread.
Haven't worked on a 392 but made 19 FPE with a 312 on 10 pumps, 14.3 CPHPs.
Thanks in part to a Mac1 steroid pump link.
https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.msg155882349#msg155882349 (https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.msg155882349#msg155882349)
l
I definitely say, especially when attempting to increase the compression on these (or any pumper) that, while I dont completely agree the steel plug would offer a strength gain, beefing up the piston pin (weak link for sure), the plug pin and link pin are going to save your 3xx from an early rebuild. I even sleeved my mac1 adjustable piston with length oriented CF tube to support additional stress and opened up all the link pins to either 3/16 or 1/4....I'm not 100% sure how much better his lever is as opposed to stock in terms of strength and longevity but I'm sure it's likely no worse. I shot him a email about it but no response.
-
A little off topic here, but now that I'm considering it....
Do both lobes on the sear engage both bands on the hammer, or is that just a redundancy measure?
I am working on the trigger now and gonna let it mate with the hammer for a while before I dip it in pot ferro. But would be nice to know if I'm missing something. I didn't do anything with it last time, but this sear is still hanging a tiny bit after working it smooth