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You could always replace the seal carrier with a piston and "O" ring, many pneumatic speargun pumps are equipped with that set-up rather than a cup type seal. Some hand pumps don't have air breather holes, they rely on the cup seal collapsing to suck air in past the seal as it is pulled backwards in the pump body, hence for those pumps you need to add air breather holes if you change the seal type. Mares pumps have breather holes, the main thing is that the breather holes don't cut the edges of the seal as it moves past the holes.
Good find.
Given your measurements, the o-ring at the end is probably a 6.07x1.78 o-ring (ID x W). Very easy to find. It's in one of the major standard series and often called "AS568-010" or at least "-010".
I should have the measurements somewhere as I made a pump adapter as one of the first things on my Mini Lathe not long ago. I based it on measurements taken from Seac and Mares pumps and it has worked flawlessly. Will check my notes later.
Thanks Gecko, good to know!I just checked the o-rings on my Seac and Mares pumps. I can not guarantee that I have not changed these o-rings, but anyways - both the pumps work.
The Seac one has a 6.75x1.78mm (ID x W) o-ring and the Mares pump an 6.35x1.78mm (ID x W).
You could always replace the seal carrier with a piston and "O" ring, many pneumatic speargun pumps are equipped with that set-up rather than a cup type seal. Some hand pumps don't have air breather holes, they rely on the cup seal collapsing to suck air in past the seal as it is pulled backwards in the pump body, hence for those pumps you need to add air breather holes if you change the seal type. Mares pumps have breather holes, the main thing is that the breather holes don't cut the edges of the seal as it moves past the holes.
Am I right in assuming that if the seal can't collapse then you'd be pulling a vacuum when you retract the pump handle? Let's say we are almost pulling a full vacuum so that, given the size of the piston, we would be in the order of pulling around 800g on each pull-back until you get to the breather hole? Does that make sense?
Now, if that is a lot or a little and will have any noticeable effect when filling a gun, I don't know.