Gotcha. I guess you must be pulling a slight vacuum on the return stroke until the piston passes the vent hole then?
Sent from my iPhone using Tapatalk
-
Welcome to the DeeperBlue.com Forums, the largest online community dedicated to Freediving, Scuba Diving and Spearfishing. To gain full access to the DeeperBlue.com Forums you must register for a free account. As a registered member you will be able to:
- Join over 44,280+ fellow diving enthusiasts from around the world on this forum
- Participate in and browse from over 516,210+ posts.
- Communicate privately with other divers from around the world.
- Post your own photos or view from 7,441+ user submitted images.
- All this and much more...
You can gain access to all this absolutely free when you register for an account, so sign up today!
Pump threads and shaft compatibility between different brands.
- Thread starterstefpix
- Start date
Thread Status: Hello
, There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.
It can take a long time to get an up-to-date response or contact with relevant users.
Gotcha. I guess you must be pulling a slight vacuum on the return stroke until the piston passes the vent hole then?
Sent from my iPhone using Tapatalk
Yes!!!!!!!!!!!!!!!!! I moved it as far to the end as possible to increase the working volume of the pump. On the Mares pump that hole is too far from the end thus reducing the volume. My pump's ID is 9.5mm as opposed the original 10mm but because of the location of the air intake hole the internal volumes are comparable. 550 strokes take my Cyrano 850 to the optimum power
Couple of ideas:
1) make a piston only with one o-ring instead of two and make it as short as possible. This way the air intake hole can be moved toward the end. The piston has to clear this hole for the air to get sucked in. This way you will increase the working volume even further given the same length of your tube
2) Use a silicon spray for the internals of the pumps. Once it dries, it turns into powder that fills tiny scratches inside making the internal surface smoother. Use silicone grease for the o-rings, not some liquid crap that does not stay in one place.
3) If you get a tube with ID of 10mm you will need the same O-ring diameter for the piston and that internal piece. Get like 50 of those and you will be set for life
Last edited:
Gotcha
An improved DIY pump that doesn't fall apart on trips is definitely on the to-do list for when I finally manage to get back to my place in China.
Thanks for indulging me on all the questions and well done on the pump!
O-rings can take a bit of stretch - the calculator will tell you if you go beyond optimal limits. Which you can but it will cost a bit of life span of the ring. I have seen some crazy stretch ratios on some o-rings in factory guns though I can't remember in which place or gun right now. But it was way over anything recommended. Off of the top of my head, perhaps the recco is about 6-8%, but would have to check. I actually think a little bit of stretch as opposed to none is good practice.
Point is, you can certainly use 9mm or 9.5mm o-ring and then just adjust the dimension of the piston groove to get a proper compression. About 15-25% is commonly recommended for dynamic (moving) seals if I recall correctly.
Actually, for the "fun" of it, I just ran a very standard AS568-010 o-ring through the calculator. That o-ring is 1.78mm in cross section and 9.63mm in OD. With a 9.5mm pump bore and a piston groove of 6.7mm you get some very usable results with compression of 9-21% and I suspect the o-ring wont be significantly overstretched (7-13%):
(I wouldn't worry about the eccentric warnings, nor the 13% stretch warning for this use).
For a 10mm bore, I would probably work with 1.5mm or 2mm rings as I can find them in all sorts of sizes in China. I think the common one to use for the Italian manufacturers in the front end of the pump, though is the 1.78m x 10.31mm (CS x OD) but that's actually not ideal for a 10mm pump bore.
[EDIT] I just found some numbers on compression in some old notes of mine:
- Static seal cross-sections are generally compressed from 10% to 40%, whereas Dynamic seals are from 10% to only 30%.
- 15-25% for dynamic 1.78mm rings (works for 1.5 - 2.0mm rings), according to Apple Rubber Seal Design Guide
- 6-20% for dynamic according to Trelleborg
- 18-32% for static 1.78mm rings (works for 1.5 - 2.0mm rings), according to Apple Rubber Seal Design Guide
- 15-30% for static according to Trelleborg
Last edited:
I found in my records: for the 10mm ID I used 6.5mm ID x 2mm thick o-rings and for 9.5mm ID I used 6mm ID x 2mm thickness o-rings. Works fine. By the way, for the Mares gun (with internal 11mm barrel like Cyrano) piston size 011 USA o-rings are perfect. They are commonly available
In my opinion for the pump the thicker o-ring like 2mm would be best since it heats quite a lot when pumping. I usually go in 100-stroke increments and rest between those
In my opinion for the pump the thicker o-ring like 2mm would be best since it heats quite a lot when pumping. I usually go in 100-stroke increments and rest between those
I do not recommend titanium. The main precaution for a pump is to avoid scratches on the inside so you need a hard grade of titanium. It is difficult to thread. Also there is another issue. When you drill that air intake hole in the back the exit opening (on the inside) needs to be polished because the piston's o-ring will catch on the chip and get damaged. Polishing that opening up is a bitch on a hard metal. I agree with you that the lighter is the pump - the better. I travel myself and sometimes come within grams of the weight limit. So I suggest to use aluminum, reduce the OD to 12mm except for the threaded part and make sure the piston is also aluminum (should not be harder than the body, you can probably even use delrin). You can get a Chinese die 14x1 that is good for aluminum for $5. Just be careful when you screw the pump into the gun to avoid crossthreading
Yeah, I actually almost made it out of 10x14mm alu tube as I had that on hand from my Mirage pumping barrels but then got caught up in the titanium fantasy... I have the dies needed for any of the threads on these guns though I mostly single point thread on the lathe now. It's overkill, but it's good practice for me.
Here are a few parts I made on the mini lathe that are still somewhat pump related;-):
An adapter for a pressure gauge in alu:
An adapter for my "ScubaFill" gadget so I can fill guns from scuba tanks - this one is in titanium:
And the measurements I use to get good results on Mares inlet valves:
((o-ring used is an 1.78x6.75mm (CS x ID))
If I recall correctly I tweaked the Mares measurements slightly to reduce the dead airspace even more. E.g. the pressure gauge hardly looses any air when taking a reading.
I also built a pressure gauge for my Mares Cyrano. First threaded, then just push-in. Both leaked air so I stopped using them. I go by feel. 550 strokes for my gun is perfect. If I go higher the shaft bends too much when loading and recoil messes up the accuracy. I spend a lot of time designing a proper slide ring with the lowest drag.
Attachments
Last edited:
A push in gauge sounds like a good idea, but I decided to stick with a threaded one. Push in would take quite a lot of force. Easily 30kgf on a normal 13mm gun and 50-60kgf on a Mirage and I just wasn't sure how well it work in reality. Did you find you could hold the push-in gauge in fairly easily or do you think they leaked because of the force pushing them back out?
If others want to have a go at building their own gauges or fill adapters, I can almost guarantee that if you go by the measurements I posted above it will be leak free. Of course, you need to "calibrate" the pin which opens the valve since if it's too long, the gauge or adapter will surely leak as you screw it in and out. That's why I use a screw type pin so I can find the sweet spot and then threadlock it in place. But many others use a friction fit dowel pin that can be tapped on until in the right position. Just keep in mind that though the thread and o-ring measurements are the same between Mares and Seac inlet valves, the length of the "depressor pin" is slightly different.
I tinker with my guns quite a lot so it's just nice to have a gauge and since I have the scuba tank way of filling them and a fridge compressor, too I have come so used to having gauges. Also, I am beginning to try to "map" how much power different shaft thicknesses need to really work well. So, for my use, I still need gauges.
If others want to have a go at building their own gauges or fill adapters, I can almost guarantee that if you go by the measurements I posted above it will be leak free. Of course, you need to "calibrate" the pin which opens the valve since if it's too long, the gauge or adapter will surely leak as you screw it in and out. That's why I use a screw type pin so I can find the sweet spot and then threadlock it in place. But many others use a friction fit dowel pin that can be tapped on until in the right position. Just keep in mind that though the thread and o-ring measurements are the same between Mares and Seac inlet valves, the length of the "depressor pin" is slightly different.
I tinker with my guns quite a lot so it's just nice to have a gauge and since I have the scuba tank way of filling them and a fridge compressor, too I have come so used to having gauges. Also, I am beginning to try to "map" how much power different shaft thicknesses need to really work well. So, for my use, I still need gauges.
Last edited:
I do not hunt on scuba so I have no compressor. You will get crucified in Europe for hunting on scuba and I will gladly be there to run the last nail through
- I hate that.Very easy to push since the area is small. I used an air pump needle integrated into my gauge - that tip is a bitch to machine
Fridge compressor... not tank compressor.
And my scubafill adapter is NOT for hunting on scuba - which you’ll never ever find me doing. But since I got into using 125-135 guns at +30bar I no longer see the charm in using a hand pump.
I’ve taken my gun on a motorbike to a local dive shop to pressurize it a handful of times. On other trips, and basically why I made the adapter in the first place, I was going to locations where friends of mine ran dive shops and I would squeeze in some freedive spearing - so always tanks around.
On my latest trip to Indo I rented a tank for a few bucks and put it in my bungalow. Normally this wouldn’t be needed but I had a highly “experimental” gun with a lot of DIY parts on it and honestly had a few issues over the weeks I used it there. But having the tank just next to me made it so much easier just to pull the gun apart and fix it for the next day.
As for hating on scuba shooters I've grown pretty ok with commercial fishermen doing it if it’s legal and they have all the permits.
Last edited:
Haven’t managed to yet. But they are catching some really nice snappers and groupers on the reefs in south China and some beautiful amberjacks in the north.
Also, supposedly some oil rigs in the south that hold some nice pelagics.
But I do freedive, mostly, with Chinese divers. Right now for example I am training at a friend’s shop in the Philippines. Did spear a little here but not an easy place at all to catch fish. But it’s getting better
Sent from my iPhone using Tapatalk
I was in Philippines on a scuba trip long time go. Very bad experience - not much fish. I am not sure I can handle South-East Asia. I prefer a minimal interaction with peopleHaven’t managed to yet. But they are catching some really nice snappers and groupers on the reefs in south China and some beautiful amberjacks in the north.
Also, supposedly some oil rigs in the south that hold some nice pelagics.
But I do freedive, mostly, with Chinese divers. Right now for example I am training at a friend’s shop in the Philippines. Did spear a little here but not an easy place at all to catch fish. But it’s getting better
Sent from my iPhone using Tapatalk
Yep. Poverty and over population makes it hard to sustain a healthy fishery here. There are some nice pockets left and some being brought back. I’ve had some very nice scuba dives here a few years ago. But on freedive spearing days I’ve seen literally miles of bombed out reefs. Not kidding you, I’ve even been in the water when I heard them blast off up ahead of us. And I’ve seen local fishermen hide their little bags of cyanide when we meet in the water. But when you know how many mouths they have to feed, you stop judging. They know it’s not cool. But it’s better than putting your kids to bed hungry.
Sent from my iPhone using Tapatalk
Sent from my iPhone using Tapatalk
I saw blown-up reefs. And I understand what you are trying to say but the judgement must be rendered. They grow amberjacks in cages in many places. They can do it in Philippines. But they don't. They are either too stupid to rob their children of a decent future, too corrupt or don't care. I have been to many countries and despite observing a lot of attempts to vilify the USA - here they actually care way more about the environment than most places I have been too. There is a reason a lot of countries are poor - people there are actually too dumb to be decent. And I must know, I came from such a place. They do not pay taxes, give bribes and destroy the environment. Cheat, steal and do other nasty stuff. And they do it in Africa, Asia, Europe, America. Some people just could not figure out that when you do all that - you actually cheat yourself.
When using a push-in gauge I would think it doesn’t matter how small you make the needle itself in terms of the forces at play. Once the air comes out of the valve, I think the force of the pressure would be acting on the full area of the 14mm bore, hence the high numbers (30-60kgf) I put in that previous post. As always, I could have missed something.
The only reason I can see for it to be a “no” is if the OD of the pin is such a tight fit into the inlet valve that you don’t leak air into the rest of the space. Because it it’s a categorical “no” then why would you even have an o-ring in the first place;-)?
I could see one potential way to make a push-in gauge work with less force on it and that would be to use a much smaller o-ring on the front face of the gauge adapter (in a trepan/face groove) which would seal on the floor of the inlet valve and not the ø14mm side walls. But the sweet spot for the length of the depressor pin would be much, much smaller so in reality, it might not work too well.
Ah Shoot! Sorry! Wasn’t thinking straight or even reading my own drawings. The bore in question is not 14mm only 10mm.
The numbers would be more like 16-32kgf (for 20-40bar pressure).
Sorry about that;-)
Still, it probably doesn't change my preference for keeping the threads on the gauge vs. push-in - especially on a high pressure gun.
@popgun pete besides my mess up on the bore diameters, what do you think about the above?
I could see one potential way to make a push-in gauge work with less force on it and that would be to use a much smaller o-ring on the front face of the gauge adapter (in a trepan/face groove) which would seal on the floor of the inlet valve and not the ø14mm side walls. But the sweet spot for the length of the depressor pin would be much, much smaller so in reality, it might not work too well.
Ah Shoot! Sorry! Wasn’t thinking straight or even reading my own drawings. The bore in question is not 14mm only 10mm.
The numbers would be more like 16-32kgf (for 20-40bar pressure).
Sorry about that;-)
Still, it probably doesn't change my preference for keeping the threads on the gauge vs. push-in - especially on a high pressure gun.
@popgun pete besides my mess up on the bore diameters, what do you think about the above?
Last edited:
When you release air from the gun - what do you do? You take a piece of hard wire or a nail and push the pin in the valve to release air. A very minimal effort is required because the surface area is tiny. Actually in case of my adapter it was difficult because I wanted to ensure that there is no air leak so it was a struggle. Anyway like I said I do not need it plus it is one less piece of equipment I have to drag around on my mighty back.
You are a good designer and I love your schematics. When I was designing my pump, I bought a thermo plastic, filled the back of the piston while it was liquid, let it harden and removed it. This is how I got the dimensions more or less right - by measuring the resulting mold
Last edited: