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Predathor Vuoto "progressive loading"


New Member
Apr 12, 2024
Hello. I have recently received an 85 cm Predathor Vuoto, and I read on this forum that if it is too difficult to load, you can use what he called "progressive loading", which seemed to be some sort of multistage loading. I see this at least alluded to in the manual where it says:

"Due to the non-return valve, you can to divide the stress load in following stages."

My question, is how does this work? Does it mean that you can press the spear in as far as you can manage, and then pull it back out, and then press it down again (perhaps even multiple times?) before locking it into place? And if so, does this mean you could just do a ton of easy pumps with the spear to load it, or what?

Thanks in advance!
Each time you push the spear into the gun the sliding piston pushes air behind it into the gun's tank. When you shoot the gun the piston is pushed forward by that air returning to the inner barrel. With a progressive loading feature a bulkhead partition in the tank causes air to be trapped by the one way valve built into the bulkhead, the air being confined in the larger forward part of the tank. Each time you push the spear that little bit further more air gets trapped in the front section of the tank and what pushes back against you is only the air in the inner barrel and air in the gun's rear chamber and that progressively lowers the pressure being loaded against. However the final pressure to latch the mechanism you have to overcome is the gun's shooting pressure, but right at the end of spear travel.

More on it here https://forums.deeperblue.com/threads/pneumatic-speargun-compression-ratio.86054/


In the Salvimar guns the one way valve and the power regulator valve are one and the same item because the Salvimar gun uses an upstream valve rather than a downstream valve. That means you push the valve head into the front tank where the pressure is being held and accumulated during progressive loading. Most guns, such as the Mares Sten, let the valve open rearwards into the rear section of the gun, hence a downstream valve opening with the pressure difference, not against it. The result of this Salvimar arrangement is high power and low power are reversed in the selector gate, low power being right back and high power forward and down in the dogleg of the gate. To indicate high power there is a small + sign in the gate, whereas lower power is marked by a minus sign, you need to look very closely to see them. Some models have these symbols marked on the tank.

To access progressive loading the selector must be in the low power position which allows the valve to close when you start muzzle loading the gun. Air pressure in the gun is provided by the separate task of using the hand pump connected to the rear inlet valve, that is how you can increase the gun's start pressure.
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One way to get used to the loading is to let some air out by removing the rear cap using the wire tool you get with each gun and then depressing the inlet valve. You can use a toothpick, just a quick push to let air out in successive bursts so that you don't let it all out. Then try loading the gun, but not to the full latch which is indicated by a click when the sear lever inside the gun engages. It it does latch you should point the gun downwards on a piece of scrap timber with the spear tip pressing hard against it and use your body weight against the gun as you pull the trigger. The spear will come out of the gun, but your body weight will slow the release. Never shoot a pneumatic gun on land, you may damage the gun and the flying spear is extremely dangerous. The guns are made to be used in water while they are submerged and only when you have a clear line of sight as to where the spear will be going.

When doing this loading practice on land the gun and spear should be wetted to aid lubrication as although the gun has oil inside it anything pressing inwards into the gun usually relies on the gun being submerged. That will not be happening on land so you need to put a hose on the gun or dunk either end in a bucket of water to get them wet, that is where the moving elements are. The spears need to be wet on a Vuoto model as the muzzle vacuum seal must be wet or you will risk tearing bits off it.

After your loading practice you can add air back into the gun using the hand pump that comes with the gun. Read the instruction book that also comes with the gun.
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The main aim of this progressive loading feature in pneumatic guns is to enable the user to latch the gun if on the first push he did not quite make it and the spear pushed forwards again which is what happens when you stop pushing on the hand loader. Now rather than repeat the same effort all over again the gun has a lower pressure in the inner barrel because air molecules have been moved into the main tank and trapped there if the selector had been set to low power, so the second loading effort is less to start the piston moving at the muzzle and then get the piston down the inner barrel to latch on the next pushing effort.

If you load a gun this way with multiple strokes then the final result is the same, but you expended more energy to do so as you have friction in the piston seal to overcome on every attempt. If you can do it in one single push then that is the most efficient way to load the gun.
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Thank you very much for the explanations, Pete. I did a couple trial loads and I think it will be fine, but I will have to see when I am in the water, and my foot/ankle doesnt have the support of the floor to help it out. I am starting to think that maybe I should have gotten one just a tad shorter, but I will have to take it for a spin in the weekend and see how it goes. Thanks again!
Thank you very much for the explanations, Pete. I did a couple trial loads and I think it will be fine, but I will have to see when I am in the water, and my foot/ankle doesnt have the support of the floor to help it out. I am starting to think that maybe I should have gotten one just a tad shorter, but I will have to take it for a spin in the weekend and see how it goes. Thanks again!
It is actually easier to load the gun with everything completely wet, try it in the shallows where you can stand on the sandy bottom and then once you have done it a few times try loading while you are floating in deeper water. Shore dives are best when trying out new guns as you can always retreat to the shoreline to sort things out while standing up in knee deep water.
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