Piston Ballast Systems

Yes will do I will sort out details over the weekend and give you instructions on how to make it,very cheap tank to build.
regards Nigel

Nigel,

I can not say thank you enough!

Peace and Cheers,
Tom

Hi Nigel
New to this but got intrested in subs when I saw one and how good it looks .. So I bought the revel kit and then I was undecided about the system to use .. both Engle and Caswell systems seem to be expensive. So building my own would seem the cheapest way of doing it, not always the best, I know.
I was thinking of a bladder or airbag system.

Could you send me the same info you sent to salmon please ?

Cheers Nick

Hi Nick,
I will post all the info on hear so that all can see.
Regards Nigel.

Hello everyone,

please give me a little space for some additional consideration about some diving systems (except gas systems because I have not had any experience with them and as Giovanni has already discussed the benefits and the drawbacks of gas systems).

Piston ballast systems
Piston ballast systems are very common in Germany and the neighbour countries and probably they are the system to be used mostly. Many modellers build the piston tanks by their own (you can see it from the photographs) or ask modeller friends who have access to a lathe. Nevertheless they are commercial available.

Giovanni has already written about some major benefits and drawbacks so I need not to repeat them; but one disadvantage that may be indeed a handicap is the long thread rod you will have with long pistons (therefore try to maximise the diameter and reduce the length).
When being filled by retracting the piston the centre of gravity will move and your model axis may incline or decline depending on the location where the piston is mounted (solution: Use two pistons in opposite working directions to compensate centre of gravity travelling or search for a position where the effect centre of gravity shift is compensated by the shift buoyancy by the change of displacement when the parts above the waterline submerge.)
Piston tanks always need sliding seals that need some notice and lubrication. In principle sliding seals will wear down by time and become unreliable and a source of leakage then (but this may last years).
Piston tanks must withstand the internal water pressure (provide sufficient stability) and the driving gear must cope with the axial force on the piston due to the water pressure. Motor and gear must have some force margin to overcome piston seal friction and the water pressure of your worst case operational depth, even when the battery is already low. Otherwise the piston stalls and your model can’t resurface any more (some modeller friends had to experience this).

Compressed air systems
Since about 15 years a number of modellers here use compressed air diving systems in combination with piston tanks for larger submarine models (approx. 1.5 metres and more, with sufficient internal space for air tank, valves, schnorchel gear and electric air compressors).
Benefits:
That’s like the “big ones” do, it is the most authentic system.
You can handle large ballast water volumes in short times (rapid submerging/ surfacing)
Once on board compressed air can be used to drive other applications (e.g. schnorchel, antenna hoisting masts)

Drawbacks:
Not suitable as a solitary system (for submerging the tank must always be filled completely, with residual air you can’t provide a sufficient static depth control), you need a secondary system (e.g. piston tank) for static depth control/ regulation.
Complex and relatively expensive
Needs a lot of space and therefore problematic to install in smaller models

Pump systems with ballast tanks
Pump systems are also in use and they exist in several designs. Some systems use car windshield washer pumps in combination with rigid or flexible tanks (needing locking valves when the pump is switched off so no water can leak in or out).
Benefits:
In general relative great freedom for selecting a location for the ballast tank.
In combination with a locking valve or when using special pump designs (hosepipe pumps/ peristaltic pumps) the tank has not to suffer the water pressure as this is blocked by the valve and/ or the pump, so the tank needs not to have a special pressure resistant cross section/ shape.
Pump systems (especially of the hosepipe type) can provide very fine ballast trimming (in combination with a motor speed controller they can trim drop by drop).
In general pump systems can pump out water against the pressure even when the battery is rather low so you can resurface.
Hosepipe pumps can act in both directions and they eliminate the need of sliding seals. When stopped they even lock the water path so that the trimming state is maintained.

Drawbacks:
In general pump systems are somewhat slower compared to other systems.
Like the piston tank they raise the internal pressure of the hull (normally this will not be a real problem when the hull volume is relative large, it can also serve as a test of hull tightness).
Like piston seals hosepipe hoses live not for ever (they should be replaced after some years to avoid leakage due to punctures).


Bellow systems e.g. as described on the ASM homepage

Benefits:
Bellow systems need no sliding seals and avoid these potential sources of leakage.
Bellow systems are simple in design and are reliable tight over long times (with the right bellows)
They can also provide very fine trimming.

Drawbacks:
When only one bellow is used there will be also a shift of the centre of gravity like with the piston tank.
In the design on the ASM homepage they need space at both ends of the pressure hull.
They also raise the internal pressure of the hull.
If installed inside the hull with pipe or hosepipe connection to outside it is not possible to fill them up or get them empty completely.
When using metal bellows (e.g. the flexible exhaust pipe section of a car) you can only use a small differential volume not to overstress the material (only approx. 20 percent volume variation)


Although the piston tank is very common here I didn’t use it for my models as I wanted to follow my hermetic design principles and avoid sliding seals under all circumstances.
For my old class 206A model S195/ U16 that is “on duty“ since 1994 I build up a system with a selfmade hosepipe pump in combination with a rigid brass tank that is vented into flexible plastic bags so an overall continuous envelope covers the dry interior of the pressure hull. The pump is driven via a speed controller and proved reliable over the years.

For my class 212A model S182/ U32 I have built up a special high pressure bellow system (able to handle 20 atmospheres) using a stainless steel bellow that is compressed and expanded by a strong gear built up with an eccentric roller bearing instead of a thread providing much lower friction and a nonlinear gear ratio that is of advantage for resurfacing. The bellow is installd inside and linked to a flexible rubber bag in the free flooded stern section via a high pressure pipe. Bellow and rubber bag are filled with a supporting non corrosive liquid (glycol) with no residual air.
This system is suited for extreme diving depths and is reliable tight but can only provide small changes in buoyancy. So the model has got a secondary system beneath the upper deck using a solenoid driven air pump in combination with air tanks with solenoid driven valves. This system needs not to work against the high water pressure – it must only survive (but it can as the solenoids are moulded).

You will see – there is not “the ideal ballast system”. Each system has its special benefits and drawbacks and you must decide for your own which is suited best for your application.

Kind regards
Hermann

I'll be using both a gas sytem and a piston system on different subs this weekend at Barrow. I do agree with everyone else about the gas system (fitted to my Small World Models Oyashio and Kilo )- I seldom seem to be able to fill the tank fully and frequently forget how many surfaces I've made. The most is about 5 per fill. The gas release valve also has a tendency to leak so the system whilst mainly satisfactory does lend itself to problems.
The piston tank (single on my UB-1 and twin on the Typhoon) are much more reliable. Norbert Bruggen told me at Dortmund a few years ago that the Engel tanks are best - to quote: "why re-invent the wheel?"
I have never had any reason to doubt his words.
Having said that - the system used by Sheerline is the most reliable of all my subs.

Andrew

A very interesting discussion, could I say.

Yes, definitely no "one right way". I suppose I have favoured the pressure tank (Sheerline type) system. Cheap and very flexible in getting it positioned in a model. As a near humorous aside, it also benefits from my less than good workmanship with regard to the servo shut off valve. A small leak here means that your sub will rise from the depths even without power!

I have never tried bags - they always seem to be difficult to source. (I was very impressed seeing George H's use of lay flat hosepipe at the Edinburgh MBC recently - looks like a very good idea.)

And Hermann - the use of stainless steel bellows is inspired! But where do you obtain them from? It meets all the needs of avoiding sliding seals.

I am working on 2 piston tanks this winter. One for 2x50 ml syringes (Thanks for the idea, Nigel) for my Resurgam and Nordenfelts and one of about a litre for my larger subs.(Based on Lothar's guide) Both with home brewed proportional control. More later.

Meanwhile putting stuff in the car, ready for Barrow tomorrow. Hoping we get a good day before the remnant of the hurricane comes in!

HI ALL

I myself use compressed air in my 12ft Gato sub, i have seen alot of people who have used ballest tanks with holes in the bottom of the tank to let water in and out of course, but because my ballest tanks take in 2 gallons of water the tank as baffle plates inside of it which is to stop water moving about. But the one big problem i had imagine that the sub is sat on the bottom with the front of the sub pointing down when you go to blow the main tanks what would happern is the holes in the back of the tank at the bottom would start to let air out instead of water because of the angle of the sub on the bottom so you would not be able to blow all the water out of the tank.So what i have in my ballest tank is valves attached to bottom of the tank for water in and out these valves have there own water senors in the bore of outlets on the bottom of the tank for water in and out. And if you end up with the problem where it would try to blow air out of the bottom of the tank instead of water the valvesa shuts off that water outlet to stop it then what would happeren is water would start to come out of the other end of the tank to make sure that all the water is blown out. Also my trim tanks work off compressed air as well, water into main tank is pumped in at 12PSI and main valves work on 240v AC. The main air tank is 140PSI


ALL THE BEST JOHN

HI,
@jonrobinson,
Can You post some pictures with these modification please?.
I'm very interested about the problem what You guest have mentioned.

This is the original 60ml syringe before alteration,sorry about the quality of the photo's,cant seam to get the focus right.

Step 1,take the syringe apart and carefully remove the rubber seal from the piston.
2,carefully cut the plundger from the piston crown (at the point that the four plundger web's meet the crown)disgard the unwanted plundger.
3,decide wether you want an open cylinder or a closed,if open cut the end off the cylinder to the length you require.

4,now place the piston on a bench face up,if you look at it you will notice four triangular web',they meet in the centre of the piston crown,these web's need to be cut away to allow insertion of a 2mm nut in the centre of them,I use a modelling knife to do this,insure that the nut is a good fit an is on centre,
SEE PHOTO.
5,when you have done that find a drill that will fit nicely through the nut you have inserted in the piston crown and drill strait through the nut and the piston,this is best done on a drill stand,but with a bit of care can be done with a hand drill.
6,now remove nut from the piston and open the hole in the piston up too 2mm,then install a new nut in the piston crown,brass or stainless is best.

7,you now need a length of 2mm brass threaded rod,6inches should be fine for most tanks,this can be made from stock brass rod or bought.
8,screw a 2mm nut an inch down the brass rod followed by a 2mm washer then screw the rod through the piston until the rod end is flush with the top of the nut installed in the piston web earlier,put a small amount of blue loctite on the threaded rod at the bottom of the piston and bring the second nut with its washer up to it and just nip it up gentle,then leave it to set,
8,re-install the seal pust the piston and rod back into the outer cylinder,and there you have it a cheapskate cylinder.
I will sort out the gearbox details tomorow.
YES I KNOW THE ROD I HAVE USED IS NOT THREADED,I COULD NOT FIND ANY SO THAT'S JUST AN OLD PROP SHAFT

Nigel, Thank you for the beginning instructions! You are a man of your word!
This is excellent. I can't wait until part 2.
Peace and Cheers,
Tom

Thanks for all the information .. Time to hit the drawing board ....

Do I unpack my Gato now ............. !!!! Or wait until I have some time to myself !!!!!

Hamster tired or the wheel broke?

Wow, sorry to hear that he is without power! Certainly waiting for the rest of the instructions builds anticipation. I just pray all is well with Nigel during this time.
Peace,
Tom

Can't blame him. I would probably be the same.

I'm SORRY to hear that.I really hope he and his family are OK.I hope the problem wheel be solved most quickly as possible.
All the best
MARIUS.

Well at least it needs a hurricane remnant to keep our Chairman quiet!

Nigel phoned me the other night to apologise about his lack of a reply - his power is still off!

I always thought of Essex being an urban county but he is right out in the country. He has a generator and apparently the electricity company is dropping off fuel to him!

He mentioned that Salmon is looking for a very small piston tank. By way of a fill in, have you seen the photo on page 49 of Norbert Bruggens book, Model Submarine Technology? (Worth getting if you haven't got it.)

This shows a "20 ml tank for the Red October plastic model" It is directly driven from a powerful servo using a rack and pinion arrangement. Very small and simple and, of course, proportional.

I just saw his book on ebay and amazon. Thank you for the tip! I will look it up. Please, let Nigele know there is no pressure and I do not want him to give it a thought at this moment. When he can, I am sure he will. I am sure he has more important things to worry about.
Peace,
Tom