Your o-ring might already work as a shock absorber? Also, Zahar's suggestion, while good, wont work with vacuum cuffs.
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Pelengas Pneumovacuum speargun
- Thread starterpopgun pete
- Start date
That o-ring has a small shock absorber action, but it is not sufficient itself for heavy sliders. I don't like this Zahar's proposition... It requires redesigning of the muzzle at least.
Because we are talking about the Pelengas slider being burst in video above it could be easily fixed just using good hydro-damping titanium slider.
If I have correct information the Pelengas titanium slider could be about 3 g? If braking distance for hydro-damper were 11 mm that would work correctly, but the gap between the shaft and the slider should be 0.05 mm and between the slider and the tail end 0.15 mm. This is for 7 mm shaft having 8 mm tail end.
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Even some initial pushing of the slider will not save the slider from being hammered by the spear tail. In my hydropneumatic guns the water around the front section of spear is driven forwards by the spear tail seal as the spear is pushed forwards from behind after the releasing valve is opened. With the trigger pulled the line loops are freed before the spear begins to travel and the annular water column around the spear pushes the line slide forwards, but water leakage slows this rate of acceleration compared with the spear driving up from behind it and the spear tail stop soon slams into the rear of the slider. This all happens in milliseconds. The hydropneumatic where this does not occur is the Aquatech 500 and its sister guns. The rear line hook will not release until the spear tail stop hits the slider, but the slider in this gun is very light and the gun is not overly powerful, although with multiple spear insertion strokes the gun can be highly charged.
Incidentally the mono shooting line shown here was that supplied with the gun, but I never used it and switched to nylon cord using the gun's second spear. As the gun did not receive a lot of use, it is rather heavy like an RPS-3 and does not float, the mono equipped spear was never needed.
Incidentally the mono shooting line shown here was that supplied with the gun, but I never used it and switched to nylon cord using the gun's second spear. As the gun did not receive a lot of use, it is rather heavy like an RPS-3 and does not float, the mono equipped spear was never needed.
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With no step inside someone may have purchased a 7 mm slider, while wanting an 8 mm, and just bored the front end out to create 8 mm all the way through as 7 mm shafts have 8 mm tails for their stop diameter. Pelengas guns were mainly available in 7 mm sizes, hence 8 mm was a more recent option in the last few years once they got rid of the bugs in the guns, and they had quite a few (e.g. broken pistons). The 8 mm titanium slider is relatively recent and I have one on order (AUD 30 including shipping).
The longer the spear then the more of a bend it can take as it is rammed well down into the barrel, thus the new Pelengas Carbon Max may be limited to 7.5 mm spears while shorter guns with 8 mm shafts use the exact same barrel bore at 12 mm (or 11.9 mm). Being a stainless steel barrel which is unlikely to score through momentary shaft rubbing I am surprised they don't take it up to an 8 mm shaft option.
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Using titanium for sliders is not true! Roughness and tears appear on the titanium surface, which scratch the harpoon and then friction increases up to the harpoon's wedge in the slider! For pneumatic vacuum systems, titanium must not be used categorically due to scratching the harpoon!
Thanks for the tip, I am going to use the titanium sliders on my wet barrel guns anyway, but good to know of this unforeseen problem.
There is a Pelengas website here: https://vk.com/pelengas_vk (actually listed on the back of the instruction book!).
https://vk.com/pelengas_vk?z=video1784889_456239023/d935f2e9aa2e63287e/pl_post_-79105414_67823
https://vk.com/pelengas_vk?z=video1784889_456239023/d935f2e9aa2e63287e/pl_post_-79105414_67823
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The 8 mm titanium slider arrived yesterday, so here it is on the weighing scale. First time I weighed it the reading was 1.89 gram, now 1.86 gram (Chinese jewellery scales).
Interesting, it is very light.. lighter than for 7 mm which was 3 g..? Are you sure your scale is OK?
Can you measure ID, OD, length... precisely? This might work well with hydro-damping. Did you try to calculate using my formulas?
Tomba - All in One barrel sealing
Water must be drained from the Tomba muzzle before loading the shaft. Otherwise the O-ring could not be pushed into the muzzle. There are a few way how this inconvenience might be solved. For usual on breath diving while preparing for next dive one can insert the shaft under water and then just...
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I weighed the titanium 8 mm slider on a digital luggage scale and the reading was zero! Then I tried a digital kitchen scale and the readings were either zero or 2 grams, so the jewellery scale must be correct. The 8 mm slider plugs into the nose cap of the 7 mm Magnum, therefore its OD must be the same as that of the 7 mm slider. The titanium 7 mm slider weighs between 2.92 and 2.94 grams and is slightly longer than the 8 mm slider.
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The Pelengas vacuum cuffs arrived, 5 of each, plus two 8 mm vacuum cuffs as an unexpected bonus.
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Interesting.. That means 8 mm slider has very thin wall..? That might be an issue.. but it is good to be very light, 1.89 g.
Next thing, if the slider OD is like for 7 mm, it is about 9 mm, what should be the tail step OD for 8 mm shaft? Usually it is 9 mm..
Pete, it seems to me that you do not have a precise caliper..?
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Could be the old type cuff just replaced with the new one, in previous spearguns?
The battery is flat in my digital callipers, I have to replace it. Pelengas say the new shape vacuum cuff goes in all the guns.
"Yes, that's right, a couple of years have switched to a new cuff shape. It fits the new muzzle nuts and is put on all models of our guns, starting in October 2017."
"Yes, that's right, a couple of years have switched to a new cuff shape. It fits the new muzzle nuts and is put on all models of our guns, starting in October 2017."
If I understood... it does not mean that the new cuff fits the old muzzle, only the new muzzle, but the new muzzle can be used in all models...
I also ordered a new Pelengas cuff on ebay, so I will soon test it with my old Salvimar muzzle. If it is not longer than the original it might fit, maybe with tiny mods..
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Hi ,
the new cuffs are a little smaller than the previous ones. But they fit the old pelengas/UBL/salvimar muzzles.
I think the old cuffs are harder than the new one. The old are the best long term solution
New battery installed.
Titanium 8 mm slider: length 17.67 mm, OD 10 mm, ID 9.16 mm, rear step 9.60 mm, bore 8.10 mm
Titanium 7 mm slider: length 18.05 mm, OD 10 mm, ID 8.10 mm, rear step 10.30 mm, bore 7.10 mm
Titanium 8 mm slider: length 17.67 mm, OD 10 mm, ID 9.16 mm, rear step 9.60 mm, bore 8.10 mm
Titanium 7 mm slider: length 18.05 mm, OD 10 mm, ID 8.10 mm, rear step 10.30 mm, bore 7.10 mm
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