water cooled MG

[joeyj]

Can some body explain to me how they keep cool. From pics I've seen there is only 1 hose leading up to the water jacket. I know or I think in WW1 there's no water pump in the can, so how does that keep the thing cool. Been wondering about this for years & could never get info on it.

[brian]

barrel has a water jacket.
when the water expands from the heat some of the water overflows into the can, that would be the single hose and can.
when the shroud gets low on water, you pour whats in the can back into the jacket.....or piss in it.
and one of the guns you're looking at is the m1917 browning water cooled.

[bac0nfat]

Originally Posted by brian

barrel has a water jacket.
when the water expands from the heat some of the water overflows into the can, that would be the single hose and can.
when the shroud gets low on water, you pour whats in the can back into the jacket.....or piss in it.
and one of the guns you're looking at is the m1917 browning water cooled.

But since the hose attaches at the bottom of the barrel shroud, what keeps all the water from flowing into the can until it's empty?

[PA Rifleman]

Originally Posted by joeyj

Can some body explain to me how they keep cool. From pics I've seen there is only 1 hose leading up to the water jacket. I know or I think in WW1 there's no water pump in the can, so how does that keep the thing cool. Been wondering about this for years & could never get info on it.

It plays games with thermodynamics.

First read the definitions of latent and intense heat. Here's a fair explanation of what's happening:

http://en.wikipedia.org/wiki/Latent_heat

Water can only remain a liquid until it reaches 212°F. It will continue to absorb latent heat, but not intense heat. As long as it remains in a liquid state, it will regulate the temperature of itself and anything else immersed in water (read: the barrel) to a maximum of 212°F. When the water changes state to steam, all bets are off -- it can take off to hundreds of degrees or even higher.

Note that it doesn't require a pump or any external pressure. It only needs to be immersed in water, which is the tank around the barrel.

As the gun fires and heats the barrel, the barrel transfers heat to the water, causing some of the water to evaporate and escape through the vent/recovery hose. This hot vapor travels down through the hose and to the bottom of a water reservoir, where it bubbles out at the bottom. The vapor now comes into direct contact with cooler water, causing it to condense and reconstitute back into water.

When the gun cools, the contents of the water jacket should partially contract due to thermodynamics. This will create low pressure in the water jacket, drawing water from the reservoir back into the cooling jacket, restoring the water level.

In practice, some steam does escape, so they do need to be topped off from time to time.

Remember, this was designed by people who lacked modern electronic computers, cars, bookface and life with Kardashians.

[PA Rifleman]

Originally Posted by bac0nfat

But since the hose attaches at the bottom of the barrel shroud, what keeps all the water from flowing into the can until it's empty?

It should pick up vapor at the top of the water jacket, otherwise it would push hot water out and trap steam. Likewise, opening the reservoir (or a bullet hole) would cause the contents of the water jacket to immediately siphon out. The water jacket might have an internal vapor pickup tube.

[ungawa]

Originally Posted by PA Rifleman

First read the definitions of latent and intense heat. Here's a fair explanation of what's happening:

http://en.wikipedia.org/wiki/Latent_heat

Never heard of "intense heat." It was always "latent" and "sensible." At least it was in the 9 thermo classes I took. I guess they changed it. They should let the rest of us know LOL.

[bigandy1966]

Heres a discussion
http://www.thehighroad.org/archive/i.../t-519154.html

[nfafan]

Think in terms of a open-loop radiator, where the crew must manually intervene to "close the loop".

In this pic of my MG08/15, you have the water jacket filler plug closest to you, and the "escape" valve behind it. The escape valve has a line that goes into a water can - or suitable substitute.



The escaping water - in the form of steam - cools and liquifies, then must be poured back into the water jacket via the filler plug.

Even though you can have sustained fire - a 200rd belt will get it steaming real good - an army must still use multiple MGs to allow for "down time" between extended firings.
Thus the many MGs deployed to hold a trenchline - it wasn't just because of interlocking fire.

In civvie shoots, we always have plenty of gal jugs nearby to keep 'em cool.

A larger view to put it in context to the rest of the gun.

[PA Rifleman]

Originally Posted by ungawa

Never heard of "intense heat." It was always "latent" and "sensible." At least it was in the 9 thermo classes I took. I guess they changed it. They should let the rest of us know LOL.

You're right!

It was sensible heat back in the day, I forgot that term when I was pecking out my post.

Among the near-useless stuff I learned from reliving the pre-W.W.II era thanks to Mom & Dad was learning about hit & miss engines (maybe they had something against throttles?). The water cooled H&M engines used a similar setup.

Here's a similar set up on a hit & miss engine, watch the segment between 47 - 51 seconds:



As long as the reservoir has enough water to cover the cylinder, the outside surface temperature of the cylinder cannot exceed 212°F.

Note the water reservoir is square, so this engine cannot be stored in freezing temperatures without draining it first. Hit or miss engines should have a "V" shaped reservoir to prevent breakage when water freezes in the cooling reservoir.

[762xIan]

I found an interesting picture:



One way to ensure firing for a long time.

In civvie shoots, we always have plenty of gal jugs nearby to keep 'em cool.

nfafan, kind of curious, do you treat the water at all that you use for cooling? I know the military didn't give a damn when these guns were in use, but your investment isn't the military. I was wondering if you use distilled water, or add NAOH to up the pH or anything to keep from getting any scale or corrosion in the water jacket and the water system.

If anyone is wondering, I work in a power plant running boilers......getting a kick out of some of the comments here.