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Oil for use in pneumatic spearguns

popgun pete

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Jul 30, 2008
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This is the oil that I use in all my pneumatic and hydropneumatic spearguns. Over the years I have gone through several bottles of it. The 500 ml packs shown are for topping up the hydraulic shock absorbers on motorcycle front suspensions, hence the common name “fork oil”.
fork oil SAE 10 R.jpg

The viscosity grade is SAE 10 or ISO 32 and it is formulated for hydraulic applications in the presence of water and is ideal for pneumatic speargun use as it has some anti-corrosive properties.
 
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Diving Gecko

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Jun 24, 2008
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Yeah, I use fork oil, too between 5-10W depending on what I can get. I think the bottle I have had for a while now is 7.5W. No testing behind it, just that I read here or perhaps on one of the Italian forums that anything more that 10W was to be avoided.

A few years ago, browsing this internet thing, I did come across a forum where folks took oil incredibly seriously. I can't recall if it was gun/rifle forum but I think it could have been. As in many other product areas, the manufacturers like to say they have invented something much better than ever before and on that forum there was a lot of talk about how the oil film attaches to parts - and whether it stays attached - in different environments of movement and temperatures. Some of the old timers said the new oils were just BS, some said there were real gains to be had for some of the high tech oils.

I remember thinking that perhaps there were some gains for us to be had, too but figuring that out didn't seem like a project I had time to undertake.
 
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popgun pete

popgun pete

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SAE 10 W has been quoted by Mares for as long as I can remember. Too viscous and the oil will not move as quickly though the transfer port during the shot, too thin and the lubrication properties are low. Unless your gun is being used in freezing icy conditions there is no need for lower grades like SAE 5 as the stuff already has viscosity modifiers formulated in it for a range of temperatures.
 
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floatingbeatle

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Nov 12, 2013
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Using Castor Oil as it was the only decent oil I had on hand at the time. Had no problems so far. Guess I'll get some fork oil for the next change. Do you know the viscosity of Castor Oil? I only went for this oil as I'd read that an older diver had been using it all his life and never had a problem with his equipment.

Sent from my U15 Pro using Tapatalk
 
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popgun pete

popgun pete

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Here is a table of Viscosity for various grades. SAE 10 grade is ISO 32. Castor oil figures are Viscosity (centistokes) 889.3 and Density (g/mL) 0.959
viscosity table.jpg
castor oil.jpg
 
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popgun pete

popgun pete

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Jul 30, 2008
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Basically I bought what I could easily obtain, a local Autospares shop stocks the stuff as well as many other automotive lubrication and cleaning products, so it was a no-brainer to walk down to the shop and buy a couple of bottles at a time. I always use it when assembling and dismantling guns, especially other people’s guns which, with a mix of carelessness and stupidity, they had allowed to seize up or otherwise fail.

The reason for the different viscosities is the damper characteristics of a motorcycle suspension will be changed by making the fluid easier or harder to pump through the openings inside the shock absorber which occurs when there are viscosity changes. When doing a lot of work in an off-road situation shock absorbers get hot as the energy being absorbed heats up the fluid.

https://rottenxxxronnie.blogspot.com/2011/09/secret-world-of-fork-oil.html
 
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vrokhlenko

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I switched to a pure silicone lube, the one that is advertised for o-rings for scuba applications. Of course they charge through the nose so I got it at an automotive store. So this is what I do: first I spray the inside of the internal barrel on my Cyrano with a pure silicone spray and let it sit for a while (when dry it turns into powder). After that I apply a liberal amount of the 100% silicone lube on the piston o-rings and make a few passes in and out of the barrel (obviously in a depressurized state). Good for a 35 days spearfishing vacation (4 shots per day average I would guess). All that liquid stuff is garbage. It does not stay in place.
I also use the same lube on my homemade Cyrano pump. I have 2 o-rings on a piston instead of the original oil wiper style. I make 500 pumps every season and change o-rings to be sure. They I still good but I have a 100 of them.

Grease:

Spray lube:
 
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popgun pete

popgun pete

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Jul 30, 2008
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Silicone can soften some types of rubber and eventually turn it to mush, so I suggest that the usual fork oil works best. I have used it for decades with no problems and you can buy the stuff at any auto spares shop that sells service materials for motorcycles. Some years ago people were squirting silicone based products into scuba regulators and it over softened the rubber diaphragms causing them to pull out of their seats and distorting as the silicone got into the rubber.
 

vrokhlenko

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Silicone can soften some types of rubber and eventually turn it to mush, so I suggest that the usual fork oil works best. I have used it for decades with no problems and you can buy the stuff at any auto spares shop that sells service materials for motorcycles. Some years ago people were squirting silicone based products into scuba regulators and it over softened the rubber diaphragms causing them to pull out of their seats and distorting as the silicone got into the rubber.
Can not agree. PURE silicone lube is absolutely harmless and can even be safely consumed by humans. Also the modern o-rings are made either of buna, nitrile or silicone rubber itself and absolutely not affected by the silicone lube. Besides I have made enough my own observations to recommend this.
 

vrokhlenko

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Also I might add that for my Cyrano the piston o-rings can be replaced by the size 011 (USA) that are $3 for a 100. Getting sourced Cyrano parts are getting next to impossible so I found a perfect substitute for the piston o-rings for next to nothing.
 
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popgun pete

popgun pete

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The oil used in the gun does not only lubricate the seals, another function is to suppress internal corrosion. Pneumatic spearguns always have some water inside them as it entered when the gun was pumped up from atmospheric water vapour that was sucked in by the hand pump. Also water can penetrate past the seals as the metal inner barrel's walls are not microscopically smooth, they always have some surface texture. As diving in the ocean can let some saltwater into the gun after extended use the anti-corrosive nature of the oil is important. Pneumatic spearguns contain dissimilar metals; stainless steel, aluminium and brass, the latter used in the valve bodies and in the presence of water reactions between these metals can occur.
 
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popgun pete

popgun pete

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Here is an article which was written in 2012.

The problem is that most pneumatic spearguns are designed for a pressure differential which is always in the same direction and hence the seals only have to operate in one direction. An "O" ring in itself has no directional preference, but the seat that it sits on may not seal equally well with the pressure differential going in either direction or during the transition from one side to the other. Certainly bi-directional sealing can be achieved and is used in many industrial hydraulic and pneumatic devices, but that will not have been necessary on the standard pneumatic speargun piston, particularly the ones that rely on the rear conical rubber or cup type seal and its flaring action under pressure which causes it to seal even better in less than perfect inner barrel bores. Those seals are also used in some hand pumps, one way they seal and push air, the other way they collapse their skirt and allow air to pass by thus causing the pump to breathe ambient air for the next pumping stroke. Water will equally well push past these seals by collapsing the rubber skirt on the seal if the pressure differential is reversed and that is a real possibility in a "sealed" vacuum barrel gun which has unintentionally flooded with water. What works in theory is not always realized in practice and I think this is why pneumatic speargun manufacturers have stayed away from designs where the seals may be overwhelmed and water can then penetrate the pressurized chambers inside the gun. Saltwater is very corrosive if it can get inside a pneumatic gun and it will then destroy smooth surfaces over a period of non-use where it can work on the same internal spot without being disturbed by any movement of the gun. Freshwater poses less of a problem and I think that this explains why hydropneumatic spearguns have persisted in places like Russia and the Ukraine and is also the reason that pneumovacuum spearguns have appeared there. Water on its own can cause corrosion, but salt in the water improves its conductivity and that allows a much faster reaction or galvanic corrosion to occur. Even 316 stainless steel, the most corrosion resistant of stainless steels, can have pits burned in it by saltwater over a period of time, so stainless steel inner barrels are not immune to corrosion.

I suspect that pneumatic speargun manufacturers, being realists, anticipate that their guns may receive little or no maintenance and hence have opted for designs which can tolerate a degree of neglect. If you are prepared to strip a gun down regularly and don't mind pumping it up on a frequent basis then more adventurous designs can be tolerated, but most gun users just want a gun that performs with little attention to maintenance and lasts for a respectable period of time before they need to replace it. Like light bulbs, manufacturers have some interest in spearguns not lasting forever and the introduction of the plastic piston has probably helped in this respect!
 

vrokhlenko

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Sep 22, 2002
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The oil used in the gun does not only lubricate the seals, another function is to suppress internal corrosion. Pneumatic spearguns always have some water inside them as it entered when the gun was pumped up from atmospheric water vapour that was sucked in by the hand pump. Also water can penetrate past the seals as the metal inner barrels walls are not microscopically smooth, they always have some surface texture. As diving in the ocean can let some saltwater into the gun after extended use the anti-corrosive nature of the oil is important. Pneumatic spearguns contain dissimilar metals, stainless steel, aluminium and brass, the latter used in the valve bodies and in the presence of water reactions between these metals can occur.
Well, my gun is 24 years old. I had problems with it when using the fork oil lubricant. Now it is perfect. And I disassemble the gun every year and never observed any water in there nor salt deposits in the inner barrel (where the silicone lube is) . Anyway I will continue to use it and as long as the inner barrel is not scratched it would serve me forever. All o-rings are in a perfect shape except for a few that I replaced and the piston o-rings are easily replaceable as well.
 

vrokhlenko

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Sep 22, 2002
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Here is an article which was written in 2012.

The problem is that most pneumatic spearguns are designed for a pressure differential which is always in the same direction and hence the seals only have to operate in one direction. An "O" ring in itself has no directional preference, but the seat that it sits on may not seal equally well with the pressure differential going in either direction or during the transition from one side to the other. Certainly bi-directional sealing can be achieved and is used in many industrial hydraulic and pneumatic devices, but that will not have been necessary on the standard pneumatic speargun piston, particularly the ones that rely on the rear conical rubber or cup type seal and its flaring action under pressure which causes it to seal even better in less than perfect inner barrel bores. Those seals are also used in some hand pumps, one way they seal and push air, the other way they collapse their skirt and allow air to pass by thus causing the pump to breathe ambient air for the next pumping stroke. Water will equally well push past these seals by collapsing the rubber skirt on the seal if the pressure differential is reversed and that is a real possibility in a "sealed" vacuum barrel gun which has unintentionally flooded with water. What works in theory is not always realized in practice and I think this is why pneumatic speargun manufacturers have stayed away from designs where the seals may be overwhelmed and water can then penetrate the pressurized chambers inside the gun. Saltwater is very corrosive if it can get inside a pneumatic gun and it will then destroy smooth surfaces over a period of non-use where it can work on the same internal spot without being disturbed by any movement of the gun. Freshwater poses less of a problem and I think that this explains why hydropneumatic spearguns have persisted in places like Russia and the Ukraine and is also the reason that pneumovacuum spearguns have appeared there. Water on its own can cause corrosion, but salt in the water improves its conductivity and that allows a much faster reaction or galvanic corrosion to occur. Even 316 stainless steel, the most corrosion resistant of stainless steels, can have pits burned in it by saltwater over a period of time, so stainless steel inner barrels are not immune to corrosion.

I suspect that pneumatic speargun manufacturers, being realists, anticipate that their guns may receive little or no maintenance and hence have opted for designs which can tolerate a degree of neglect. If you are prepared to strip a gun down regularly and don't mind pumping it up on a frequent basis then more adventurous designs can be tolerated, but most gun users just want a gun that performs with little attention to maintenance and lasts for a respectable period of time before they need to replace it. Like light bulbs, manufacturers have some interest in spearguns not lasting forever and the introduction of the plastic piston has probably helped in this respect!
I have no option but to depressurize gun for travel. So I pump it once or twice a year and lubricate the piston when doing so. You are partially right about Russia/Ukraine (I should know), the hydropneumatic guns are popular because they are 100% safe to load and the shooting power can be easily regulated with the number of pumping strokes. Also the short gun can be extremely powerful and useful in the dark water. They are also the most expensive to make but in the USSR times they were manufactured from the stolen materials and by extremely skilled welders and machinist with the grain alcohol being the currency. I have been out of there for 30 years so not sure what the deal is now. But the best guns were imprevious to elements since they were made out of titanium that has an absolutely artificially expensive cost in the West.
I have a custom-made HP gun. It is a piece of art! But I do not hunt with it :)
 
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popgun pete

popgun pete

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Jul 30, 2008
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744
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Australia
My oldest pneumatic gun is still working and was made in 1967, the first "Sten", and it has always used either SAE 10 W anti-corrosive oil (as recommended by Mares) or fork oil SAE 10. It is the silver tank gun with the black aiming stripe.
muzzles R.jpg

grip rear view R.jpg

Sten Magnum SL R.jpg

grips R.jpg
 
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