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Old 12-17-2006, 05:22 PM   #1
popgun pete
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Alcedo Hydra Help required

About 5 years ago I came across an Alcedo Hydra hydropneumatic speargun that had seized up completely. The gun had been stored unpurged (no fresh water flush out) after an ocean dive and corrosion had subsequently done its work, but the alloy castings were in surprisingly good shape, no pitting, just a rime of white surface corrosion in the close contact spots which scrapes off to reveal an intact surface underneath. Using a full arsenal of pneumatic speargun dismantling tools, I gradually got the gun apart without damaging anything, even using the power of ice expansion to drive the seized firing valve out of the centre section housing through iterative steps of flooding and refreezing the dismantled centre section.

Why I am writing is the external hydropump, or sur-compressor, has defied all attempts by myself to budge it, even though it is easily screwed out of the gun. I have taken off a rear end cap (under the rubber pump knob) after unscrewing a nut that held it on a thin shaft protruding from the rear of the pump. The shaft is centred in a stainless steel disk with four round indentations like some sort of security keying device. I made a special tool to engage two of these indentations, but could not get the disk to budge, nor can the shaft be driven out, either from the rear or by hitting the pump at the front end, where it is threaded for attachment into the gun. Inquiries into Italy drew zero responses, so now I am looking elsewhere for info from someone who knows about the gun.

The hydropump, not all Hydra models had it, has now been marinating in WD40 for five years, every now and then I attack it with a renewed bout of enthusiasm, only to be met by failure. I cannot risk damaging the parts and anything that will remove the aluminium oxide build-up inside the pump (the most obvious culprit) will strip the blue anodising from the pump.

Anyone out there with some knowledge, or ideas, or is this going to be a wall hanger (it probably will be anyway)? An exploded parts diagram would be very welcome, but I know every inch of the gun, bar the insides of the hydropump. Staring balefully at the gun has not worked either, and it has received plenty of that over the last five years. The gun has absorbed many man-hours of my work and I would hate to give up on it at this stage.

I do not really need this as a shooter as I already have a full complement of underwater weapons, all propulsion types, so please no "get yourself a band gun" comments.
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Old 12-22-2006, 11:46 AM   #2
Asturven
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Re: Alcedo Hydra Help required

Let me ask for a diagram in some forums in Spain and with a friend that has a repair shop.

I saw several of them in his shop some years ago.

Cheers

Ivan

ivan@freediveforlife.com
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Old 12-22-2006, 01:29 PM   #3
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Re: Alcedo Hydra Help required

Thanks, that sure would help. So far I have limited the twisting force that I have applied to avoid breaking things, as I am only able to guess the rear hydropump's interior construction. Knowing what threads onto, or into, what would save me from stripping any aluminum threaded parts. I would say the damage occurred when the original owner put the gun away unwashed and then found at the start of the next season that the gun was totally seized.
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Old 05-10-2020, 05:23 PM   #4
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Re: Alcedo Hydra Help required

Answers.

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Old 05-10-2020, 06:16 PM   #5
StukNotAnchored
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Re: Alcedo Hydra Help required

How about a soak in white vinegar?
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Old 05-10-2020, 07:35 PM   #6
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Re: Alcedo Hydra Help required

Quote:
Originally Posted by StukNotAnchored View Post
How about a soak in white vinegar?
Vinegar was tried, the villain is aluminium oxide. Aluminium in connection with stainless steel if left marinating in hydrated salt crystals forms a white powder of aluminium oxide. This oxide production expands to fill up every available space and virtually cements screw threads together. To undo such items requires such high torques that you risk shearing the alloy parts before the screw threads budge. Also the aluminium parts get weakened by tiny holes of corrosion that in a sense white ants the alloy. Thus alloy pieces flake off and chip where there are screw threads. The problem with the gun was it was stored without washing it out and after a few years the hydropump was toast. The pump rod needle also corroded making it unable to slide through its seal in the top of the pump body which has also deteriorated. The best solution would be to remake the pump, but ultimately these guns are a curiosity and are not worth using these days. There is a reason that they disappeared.

Bear in mind that this thread is 14 years old, I decided to complete it if someone does a search.
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Old 05-10-2020, 07:51 PM   #7
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Re: Alcedo Hydra Help required

Here is a NOS example of the "Hydra II", which is the gun most people have seen at some time or other. When submerging cue the theme music from "Voyage to the Bottom of the Sea".

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