Using Hydrostatic Pressure to Boost Stored Energy

You are correct, your attached sketch is very difficult to read to gather sufficient information to evaluate your needs.

Perhaps if you separated it into two separate (larger) images, we could see what you see and give you some help.

Is this better?

As far as the function of the cutting device, it will depend on how long it takes to make the cut, and how long it runs on 30 gallons. It appears the initial driving pressure is 5K psig, pumped in. IF you can pump the water in at depth, why not keep pumping to run the cutter indefinitely?

The hydrostatics part is relatively simple math surrounding the diameters of pistons, residual cylinder volume after compressing the nitrogen, initial cylinder volume etc.

At 1000 FSW ... you aren't trying to cut a 'transatlantic cable' are you...?

The engineering and machining going into your 'power source' will be pricey enough, such that (...I would hope...) you are not trying to re-invent the proverbial wheel, here...(?) As JS had suggested: "why not keep pumping to run the cutter indefinitely?"

Have you looked-into all possibilities that already exist, "out-there"...?

Shallower work is accomplished "all-the-time" using monster clippers:

... Of course , THESE don't give the "Nice Clean" cut, as you would achieve using a Wach's Saw ... (also hydraulically-operated).

The major hurdle in going to 1000 feet using such a tool ("off-the-shelf") is simply the weight of the hydraulic HOSE hanging in the water.

Certainly NOT an insurmountable difficulty. Proper "Hose Management" engineering ... (buoyancy factors and 'hold-backs') could be produced FAR easier than the device you are currently thinking of tackling.

Just my two-cents worth. Wishing you success...(either way).

Thanks for the comments and pointers, we are not cutting transatlantic cables but definitely want to cut and retrieve something from the seabed. Can't continuously pump as the plan is to have a very lightweight system deployed from a smallish vessel and deployed to the target with a small ROV. At the moment we are just trying to ascertain if we can deliver the required volume at the required pressure by using the hydrostatic to assist. If it's not feasible we will have to deploy a far larger chamber.

I remain perplexed ... ... given the 'nitrogen' in chamber 'C', what possible assistance could be gained from the ambient pressure at that depth (the 'hydrostatic' pressure)?

In order for the N to achieve ANY 'push' on the piston (thus delivering the 5kpsi water to the tool), the nitrogen would have to be at (considerably) GREATER pressure than 5k ... n'est-ce-pas?

So ... what is the 400-500 psi ('hydrostatic') going to achieve... (by opening the valve)...?

That's what I'm asking. When the cutting device is activated the fluid in chamber-A is being driven into the cutter by the N2 which is expanding (and losing pressure) to drive the fluid. Wouldn't the hydrostatic acting on the 12" diameter piston help the N2 to maintain pressure?

I 'blew-up' your sketch such that I measured 3mm width at "Chamber-C", giving 37mm ('measured') from 'bottom-of-piston' to its "Bottomed-Out" position (max-travel). [At this scale, the ID of the cylinder measures about 20mm.]

Note: clearly , these measurements are for "Ratio-Use" ONLY ... things are certainly NOT sketched-out To-Scale, as your 6" ID tube would have to be 20 feet in length to hold the 30-gals of water (rounded).

Continuing: in order for your "nearly-bottomed-out" piston to STILL be providing sufficient "push", to deliver the 5kpsi water to the cutter, IT (the "full_volume" of the piston's cylinder) must be at something_above 5000psi......

... which means , that at "full compression" (at present scale), that 3/40ths volume of nitrogen, would have to be ('starting-out') at a ... well, "figure it out" ... let's just say a *ridiculous* pressure. (where is SolarEagle to tell us if that's approaching "liquification", for N ...)?

If you can figure out how to machine this design so as to function, I believe you will establish some altogether new bars ("heights") for the industry. For starters, try beginning with a "To Scale" drawing that will portray things as they would NEED to be using current "state-of-the-art" knowledge. I think you'll find that it is much larger than you would have hoped for.

There *are* submersible power units for the "typical" hydraulics-units previously mentioned ...

Wishing you success ~

Can your machine be allowed to emit gas? Compressed nitrogen does not weigh much. Also, you could also produce gas from seawater (depends on how daring you are), by using electricity to produce hydrogen (produces a greater volume of gas than the oxygen), or you could have dry ice on board the ROV, and convert this to gas using a seawater heat exchanger, and also allow the ROV to maintain ballast by taking on an equivalent weight of water.

... You stated (in #5) "...definitely want to cut and retrieve something from the seabed."

Clearly, in only 1000' of water, you aren't after something off the Titanic <grin>.

If the "something" isn't an abandoned pipeline (clearly not, considering the vessel with which you hope to accomplish same), I cannot HELP but keep wondering: whattheheyizzit...?

Does it REQUIRE a "Clean_Cut" (like the Wach's Saw, link given in Post#4), would achieve)?

Or ... (where-in-the-WORLD is the item-of-concern?) ... could you deploy an appropriate shaped-charge? (any "turtle-watchers" required to be on board?)

Or, could your "Tube" idea blast a "guillotine" type wedge thru whatever it is...?

J u s t "scratchin my head" still...

Tom,

Many thanks for your interest but I cant reveal the purpose as yet. A prototype is being made to test the theory and I'll update this thread when the results are in.

Will be anxious to hear how it works-out...(here's praying for *safety*, for all involved...as well as Success...!).