I'd like to follow this thread......
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.
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.
Quote from: Hack21 on July 08, 2021, 07:21:23 PMThe 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.
Quote from: Hack21 on July 08, 2021, 07:21:23 PMThe 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
Quote from: antithesis on July 08, 2021, 07:48:12 PMQuote from: Hack21 on July 08, 2021, 07:21:23 PMThe 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 canIt 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
Quote from: Hack21 on July 08, 2021, 08:04:11 PMQuote from: antithesis on July 08, 2021, 07:48:12 PMQuote from: Hack21 on July 08, 2021, 07:21:23 PMThe 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 canIt 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#msg156063564Was 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 iI dont think it's going to hurt anything. But I understand that at higher pressures every little bit of dead space counts
Quote from: antithesis on July 09, 2021, 12:10:52 AMQuote from: Hack21 on July 08, 2021, 08:04:11 PMQuote from: antithesis on July 08, 2021, 07:48:12 PMQuote from: Hack21 on July 08, 2021, 07:21:23 PMThe 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 canIt 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#msg156063564Was 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 iI dont think it's going to hurt anything. But I understand that at higher pressures every little bit of dead space countsYes, 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 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.
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