Sea rocket info

[popgun pete]

I have had a spare Sea Rocket handle sent to me by Mel Brown from the AUF spearfishing museum for a few years now which has always frustrated me in disassembling its back end. Not wishing to bust anything, I purchased a socket spanner to open the front end up. What I found inside tells me how the gun works. It is a valve system not unlike the hydraulic locking chamber valve in the Aquatech guns where water under header tank pressure from a gas reservoir causes the gun to shoot when you unbalance the valve. The Sea Hornet Sea Rocket works in exactly the same way, but because gas is involved and its expansion is what drives the spear the spaces inside the locking chamber are much bigger because this volume of gas expanding is what blows the spear out of the barrel. I am waiting now on the delivery of a pin vice to remove the troublesome to remove pin in the safety wheel. I have tried to pull it out or knock it out, but now I think that it is screwed in, like the end of a bicycle wheel spoke, which is what it may be if it is a tiny screw thread. More to follow.

Bear in mind the famous Pelletier and its modern recreation as the MACO2 are both mechanical latch guns that grasp the spear tail; the Sea Rocket is a far superior valve system able to meter out the shots from its gas supply. Manufactured in Australia it was able to deal with the monsters in off-shore lairs which considered themselves invulnerable to attack by the double-ended squids with their detachable shooting arms. That folks, is us.

The releasing valve is shown at the top in about the same position that it sits in the gun. That conical tip on the left goes into a tapered seat in nylon embedded in the rear of the chromed nose cap. What that tip withdraws as the pressure balance is lost via the trigger valve opening up its locking chamber the gas already transferred to the chrome cylinder blasts into the inner barrel rear end sending the spear shaft flying.

 

[popgun pete]

More photos of the Sea Rocket innards.

 

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The rear end of the releasing valve is another clue as to how the gun works. This fat rubber packing type seal is not an absolute fit, it is slightly loose in the cylinder bore to allow a leak path across the seal. Either that or it would have a transfer valve built into it, but from its rear side we can see that there isn't one.

 

[popgun pete]

How the gun works is with the rear gas cylinder connected and opened then all the chambers in the handle filled up with gas. Gas can get past the releasing valve rear seal as it has plenty of time to do so. When the gun shoots the trigger valve, which we will look at next, empties the gas from behind the releasing valve. That means the barrel interior is at ambient pressure and so now is the volume behind the releasing valve, but the barrel bore is much smaller in cross section than the cross section behind the releasing valve, hence the force rearwards is greater than that trying to send the releasing valve forwards. The net effect is the greater rearwards force uncorks the rear entrance to the inner barrel and then the gun shoots as expanding gas pours down the inner barrel, the gas being at around 900 psi after going from liquid CO2 to the vapour state. Ambient temperature has a bearing on this launch pressure as the gas needs heat to expand. Very simple and nothing to really go wrong, except that some gas might also head out via the dump pipe, you need some to go out, but not too much, that is why the dump pipe bore is restricted in diameter.

 

[popgun pete]

Although the scales are completely different you can see the similarity between the releasing valves on an Aquatech hydropneumatic gun and an expellable gas gun. At the front end they both close off a smaller bore size than that at the rear where a biasing spring is located. There is such a spring in the Sea Rocket, but I have yet to fish it out. The pressure imbalance at either end allows the releasing valve to be fired by the high pressure that was responsible for keeping it closed, a very elegant and simple idea.