Submarine Phrases

[redboat219]

Can anyone explain what the phrase "equalize pressure" mean. I came across it while reading Das Boot.

[JWLaRue]

Re: Submarine Phrases

When a (WW2) submarine fires a torpedo, a charge of high pressure air is used to push the torpedo out of the torpedo tube. This air is then cycled back into the sub's pressure hull to reduce/eliminate that air from coming to the surface and giving away the position of the sub.

This causes the internal pressure of the sub to increase. When it comes time to surface, it then becomes necessary to reduce that build-up of pressure down to that of the external atmosphere. If this were not done before opening the conning tower hatch, it could cause a large enough blast of air to push a person out of the conning tower. If the pressure differential were high enough, it might not be possible to even open the hatch.

-Jeff

[bigdave]

Re: Submarine Phrases

Very interesting Jeff.
But my question is would not the air pushing the torpedo out the tube leave the tube with the torpedo?
Or am I missing something (as usual) BD.

[JWLaRue]

Re: Submarine Phrases

....excellent question. We need a submariner with experience in these systems to explain the details of how the valves and associated plumbing works. From what I recall, the air charge is used to push a slug of water, which in turn pushes the torpedo out the tube with the air being contained within the valving arrangement.

Hopefully one of our folks can confirm or correct?

-Jeff

[boss subfixer]

Re: Submarine Phrases

Jeff you are essentially correct. Basically water is drawn into an impulse tank which gets pressurized and that is what pushes the torpedo out.
Check out this link for fleet boats, I'm pretty sure the basics are still the same.

http://www.maritime.org/fleetsub/tubes/index.htm

[JWLaRue]

Re: Submarine Phrases

Don,

Excellent reference pointer...and thanks for the confirmation of my non-expert answer.

-Jeff

[redboat219]

Re: Submarine Phrases

Is this related to the practice of releasing compressed air into the hull during a dive to pressurize the hull to check for leaks? How much is the air inside pressurized anyway, would it cause the bends if you're subjected to it during long dives?

[don prince]

Re: Submarine Phrases

Hello All,

I may be all wet, but I thought there was a steel plate that was set against the inner torpedo tube door. The torpedo is loaded into the tube , the door is closed, then the tube is flooded and the air is exhausted into the pressure hull. The outer door is opened and High Pressure is used to push the steel plate forward and eject the torpedo.

The steel plate has extensions that ride in groves in the torpedo tube, but the groves end and capture the plate and the charged air. The air is exhausted into the pressure hull as external water pressure pushes the plate back into the inner door. The outer door is closed and the water is captured into a reserve water tank. This weight will offset the weight of the torpedo that was just fired.

Regards,
Don_

[subicman]

Re: Submarine Phrases

Hi Guys,

Modern torpedo tubes such as those on a LA Class (SEAWOLF and VA boats are slightly different, but i can't speak to them yet), like Don said, have an impulse tank attached to either the port or stbd bank. The torpedo tube is flooded down with water from a water round torpedo (WRT) tank. the tube is equalized with sea pressure then using piping connected to the hull. The impulse tank is opened directly to sea via a third shutter door located behind and below the torpedo tube shutters. HP air from onboard storage flasks (2000 psi) is release by actuating a firing valve which also uses air, (400 psi) to the opposite end of a hydraluic ram inside of the impulse tank. This pushes water up into the tube via what is called a slide valve. Because a liquid cannot be compressed, the resulting motion ejects the torpedo/tomahawk from the tube at a force that is greater than 2 G's. The torpedo will start when a series of sensors sense that the proper firing voltage and acceleration has been achieved. When the ram is returned to battery (more air) all the expended air in the impulse tank is vented inboard, same with the rertuen air, the air used to drain the tube, and the firing air. it is all vented inboard. The reason why is because we compress our own hp air from what is sealed onboard when we dive, causing a vacuum. Thus anything used should return, to kep us at atmosphere. if we equalize with atmosphere before we expend any hp air, then there can be a pressure on the boat when the air is vented back in. We don't get the bends because we do not pressurize or go into a vacuum beyond a few inches of mercury. (+/- 6")

Tim
Qualified Submarines 1991-still going strong

[JWLaRue]

Re: Submarine Phrases

The torpedo will start when a series of sensors sense that the proper firing voltage and acceleration has been achieved.

The WW2 German G7 torpedoes had a mechanical trigger switch on the top side of the main body which was tripped when the torpedo was pished out of the tube.

I *think* the American WW2 torpedoes did the same....

-Jeff

[don prince]

Re: Submarine Phrases

Hello All,

Forward Torpedo Room of U-570 showing breech door of port upper tube (open to show torpedo firing piston0 - impulse air passes from oblong port (at about one o'clock), around one edge of the piston skirt, to the back of the piston.


This photo was taken of U-995 inner door...


U-995 outer door...


I hope this helps.
Regards,
Don_

[don prince]

Re: Submarine Phrases

Better yet, go to this web site....

http://www.ubootwaffe.pl/component/opti ... view,items

Regards,
Don_