Mugsie, there are two ways usually used to water cool a machine gun.
1. Passive system
2. Active system
And there is also a tube running inside the water jacket higher up over the top of the barrel. This is called the "steam tube". This steam tube has holes in its rear and front to allow steam from the heated water to go into this tube and flow into what is known as a "steam chest". To keep the non steamed water from just flowing out the steam tube's front or rear holes when the gun is not perfectly horizontal, there is a sliding piece that fits over the steam tube or can even be a small piston like thing inside the steam tube, that acts as a sliding valve so that no matter whether the gun in tipped downward or upward, this sliding valve will slide by gravity to cover the holes in the steam tube so the water will not leak out. Tip the gun downward and the water in the water jacket will all go to the end and leave an air void at the elevated end of the water jacket and the sliding valve on the steam tube will also slide to the downward end of the steam tube and stop any water from leaking out. The same is true if you tip the gun upwards. But the steam can still go out the steam tube because whichever end still has the air void that is not being tipped downward will still have its holes open on the steam tube while the other end of the steam tube that is tipped downward and covered with water cannot leak out because of the sliding valve on the steam tube.
Here's a below pic comparing a real Browning 1917 water cooled to my ruger 10/22 dress up kit 1st water cooled prototype. You can see the screw in the upper front of the Browning's water jacket. This is where the steam tube in located over the top of the barrel.
Where a particular gun uses a steam tube in its water jacket, the steam tube goes to the fitting or tube going out the bottom of the water jacket. So what you have with using a steam tube, is the tube goes over the top of the barrel inside the water jacket, then this same steam tube, or a tube braised to it, while still inside the water jacket, goes to the fitting on the bottom of the water jacket. Visualize a steam tube inside the water jacket over the top of the barrel. Now visualize inside the water jacket another short tube connected to that steam tube and that shorter section of tube goes downward to a fitting that exits out the bottom of the water jacket.
That explains the steam tube and steam tube valve. Now I'll explain the differences between the two types of active and passive systems I mentioned. Keep in mind that they MAY or MAY NOT utilize a steam tube.
My two water cooled ruger 10/22's DO NOT use a steam tube.
1. Passive water cooling system.
Is when you have a water jacket (with or without a steam tube) and you also have a fitting or tube that exits the bottom area of the water jacket wherein this tube or fitting has a SINGLE hose attached to it that the other end of that hose goes into a can, bucket, radiator or steam chest. Here are some pics that show the tube attached to the water jacket going to a can, radiator or steam chest.....
Browning.
Browning.
Browning.
Two below pics of my Ruger 10/22 water cooled dress up stock with passive water cooling system with water jacket hose attached to a radiator.
In below pic you can also see my very first prototype dress up kit which is an air cooled version.
The water cooled version was actually my 2nd prototype.
Now here is what happens in a passive water cooling system. The water heats up from the heat of the barrel firing. Steam goes into the upper part of the water jacket and goes into the holes in the steam tube where it then goes from the steam tube into the hose and into a radiator, can or steam chest to cool. When this happens there are two different ways the steam can get back into the water jacket after it cools to become water again.
If you stop firing to stop creating heat, as the water jacket cools and if your hose (going into your bucket, can, radiator or steam chest is not open to air and its hose end is under water, then the cooling of the water jacket will cause a vacuum in the water jacket that will cause the water to flow back upwards into the water jacket. But this only happens if you stop firing and the water jacket cools. So how does one get the cooled water that is now in the bucket, can, radiator or steam chest back into the water jacket if the water jacket and the water still in it is not cool?
You unscrew the water filler cap on the water jacket so air can flow out of the top of the water jacket when you lift up the container holding the cooled water and let it gravity flow back into the water jacket.
2. Active water cooling system.
Is when you have either a manually operated pump or an electrical, gas or recoil operated pump. It also necessitates using two hoses. One hose to allow the steam to go out and another hose to allow water to be recirculated back into the water jacket.
Here is a picture of a Browning with a steam chest that has a manual pump handle to allow the pump in the steam chest to be manually pumped. Notice also the two hoses attached to the steam chest and the gun. One to allow steam to escape and one to manually pump water back into the water jacket......
Active water cooling systems were USUALLY but not always used on guns that were on a ship or in a fortification that would allow the use of extra containers of water and non manual pumps. They were not USUALLY used in the field, and when they were, they were usually the type that used a hand operated pump.
That's the passive and active ways to cool a machine gun.
When I built my first water cooled prototype for a dress up kit for the Ruger 10/22 rifle, I thought about using a steam tube. But decided it was too complicated and would increase expense. I decided on using another way to cool the barrel.
My system is passive but could very easily be adapted to be an active pumped system too. Here is how my system works in its passive mode.
I have fired 2000 rds at a time (with time out for 50 rd mag reloads) with the water jacket only getting just a little bit warm even without a radiator attached with just cracking open my water jacket's filler cap a bit to allow any pressure from heated and therefore expanded water to escape.
What I DO worry about is expansion of the coolant or heated air more so than steam. I worried about that in initial test firings so I cracked open my water jacket's filler cap to make sure I didn't build any pressure up inside the water jacket that could even have a possibility of cracking it. Probably wouldn't but I like safety margins. I didn't like having to crack open my filler tube cap like that, since if I elevated the gun or tipped it downward, it could possibly cause coolant to leak out the slightly cracked open top mounted filler tube cap. Didn't happen in test firings but I didn't even want the POSSIBILITY of it happening ever. I decided to find a way to not have to crack that cap open. That's one reason I came up with my radiator system along with also wanting cooling overkill.
As a certified diver I have some knowledge of pressures and vacuums. Instead of having a steam tube inside my water jacket that would run over the top of my coolant and only allow steam to escape as in the full size guns, my design just allows for any expanding coolant or any expanding air if there is any air at all inside the water jacket, and if fired enough to heat it enough, even steam, to expand and overcome the natural vacuum inside the water jacket and through pressure push into the hose and into the radiator to cool. If you fired the gun enough to get it hot enough for the coolant and or air or steam to do that. Which although unlikely, is possible.
I wanted overkill for cooling and expansion. There is a tiny hole drilled through a brass cap screwed onto a fitting on the radiator to allow any expanding air coming from the water jacket into the radiator to exhaust to the atmosphere. If I drilled a tiny hole in my water jacket's filler cap, the coolant would leak right out the water jacket into and through the hose and into the radiator until it leaked out the tiny hole in the radiator's fitting and would not stay in the water jacket at all. Kind of like if you put a straw into water, put your finger over the end and pull it out. The straw keeps the water inside until you release your finger. So the cap on the water jacket is not drilled. By keeping a slight vacuum in my water jacket it keeps the coolant in the jacket until it expands enough to overcome that slight vacuum and pushes into the hose and into the radiator.
Then as the coolant, air or steam cools, it contracts and is sucked back up into the water jacket because since it cooled it is no longer creating pressure and that now lack of pressure creates a vacuum that will suck it back into the water jacket, filling it and the hole in the radiator's fitting will allow air to again enter the radiator. But that is only one of two ways to cool the gun with my cooling system and that would only happen if you fired literally thousands of rounds through it to heat it enough to get it to do that. It is also a slow way to cool the coolant because it has to get very hot to push out of the water jacket and into the tube and then into the radiator. That takes a moderate bit of pressure to do that and in reality most of the time it will only enter the tube and not even get to the radiator unless you shot the hell out of it and heated it enough to create enough pressure for the coolant to pressurize enough to reach the radiator. So this version of my system is actually more to allow expansion than to allow cooling. It cools some but not as well as the other thing I am about to describe that I can also do with my system.
The way to quickly cool the gun if the jacket's surface starts to feel hot, is to unscrew the water jacket's filler cap, this will allow the water jacket's coolant to completely drain into the radiator and the air in the radiator will exhaust into the atmosphere through the tiny hole in the radiator's fitting as it fills with coolant. This will also allow cool air to enter your water jacket through its filler tube and help cool the inside of the water jacket. Once coolant starts to come out of the tiny hole in the radiator's fitting, screw the water jacket's filler tube cap back on and that will create a vacuum to stop the flow into the radiator from the water jacket. Let the coolant sit in the radiator a few minutes so the fins can radiate the heat away. Then lift the radiator up over the top of the water jacket, unscrew the water jacket's filler cap to allow the air in the water jacket to escape and allow the now cooled coolant to flow back into the water jacket, screw the water jacket's filler tube cap back down to reactivate the vacuum and you are ready to go again.
This sounds complicated but it really isn't. That's the fastest way to cool the coolant. You see, I really don't need to cool that much since test firings have shown me that even after 2000 rounds the water jacket is barely warm. So my primary concern was expansion and avoiding cracking my water jacket. That's the main reason I fabricated the hose and radiator, so the expansion had somewhere to go without me having to crack open my water jacket's filler cap to let it out, and....this system does allow cooling through convection and also manually. As I said, it sounds complicated but it really isn't.
Now when I finally get around to making a belt feed for it, I may change it to an active pump system with two hoses and an electric aquarium pump plugged into an inverter attached to a battery and dropped into a bucket of water if the water jacket gets really hot in test firings, but for now, this is all I need.
Here's a final photo of my latest 3rd prototype which is my 2nd water cooled prototype, (1st prototype was an air cooled model) with its larger water filling fitting than my first water cooled model to make it much easier and faster to fill the water jacket with water. It's not completely finished yet, still lots more to do, but the water jacket currently holds water and doesn't leak at all. Actually this 3rd prototype can be changed out in about ten seconds from a water cooled look-a-like of a Browning 1917, to an air cooled look-a-like of a Browning 1919, and will attach to
ANY inexpensive camera tripod. I've incorporated all kinds of improvements into it that I learned from making the first two prototypes. Like an improved way to seal the water jacket to the barrel but by just unscrewing the flash hider the whole water jacket comes off and a perforated air cooling shroud can be installed in its place in just a few seconds, making it a quick change between an air cooled to a water cooled version in just seconds. A built in bolt recoil buffer built into the rear of the real Ruger receiver attachment point that holds the Ruger receiver to the fake receiver. An improved way to attach the real Ruger receiver inside the fake receiver that is much more sturdy than my first two prototypes (and they are pretty sturdy as they are!). A standardized fake receiver that works for either the water or air cooled versions. An improved way to keep the air cooled shroud and the water jacket from rotating around the barrel. An improved and simplified sighting system (not seen in attached photos yet). An improved way to attach it to an inexpensive camera tripod so no expensive real machine gun tripod is necessary. This 3rd prototype will be the embodiment of everything I have learned over four years of designing and building these prototypes.
I designed my dress up stocks around the factory Ruger receiver so nothing is modified at all on the factory Ruger receiver in any way.
3rd prototype, (2nd water cooled prototype) that also quick changes to an air cooled model.
All that's left to do is to fabricate the sights and tripod mount for fitting to a standard camera tripod.
With 50 rd MWG mag in gun.
With 25 rd Tactical Innovations mag in gun
Quick changed to an air cooled model. Pic taken before I drilled & tapped & added hex button screws to
the top cover also before I rounded ejection port ends.
I hope this helped you understand how water cooling a gun works Mugsie.
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