Piston Ballast Systems

Can you help me figure out how to build a piston tank?
what or how do you make a spindle nut? and how does this connect to the motor?
I notice that it is used a lot in Europe and not so much here across the pond, but it looks like the best choice for static diving in the sub I want to build. Can you help me or point me in the right direction? are there any drawings?

I have access to a lathe, granted it is older than most of the submarines we are building models of, but it is functioning.


Thank you!
Regards,
Tom

Hi Tom,
You may also want to register at www.rcboot.de
They have lots of different piston ballast tank custom designs there.
Regards,
Giovanni

Thank you for the direction. I went looking, but I am having trouble even with Google Translate finding articles. Can you guide me on ones you have found?

Cheers,
Tom

I've only just started making my own - so I'm no expert on piston tanks. They are probably the most difficult dive system to build - because the pistons/cylinders need to be machined.

The original document I found very helpful was by Lothar Mentz in Sonar. The original link to the website no longer works(It was 2009) but this reference from his document may help you track it down. (You will need to translate the document from the German - Google Translate does quite a good job.) (I don't want to send you copies because that would not be with Lothar's permission.)

Kolbentank im Selbstbau Piston Tank in DIY
von Lothar Mentz aus SONAR 9 Lothar Mentz from SONAR 9

I wouldn't contemplate making one unless I had access to a lathe. (I have a Taig/Peatol which is small but OK) So don't start unless you have access to machining, I would say. Plenty of other dive systems available with all their advantages and disadvantages - see the AMS website for a description.

Nigel E is also a dab hand with piston tanks and will hopefully chip in.

A photo grabbbed from the original article (I'm sure that Lothar wouldn't mind.) It shows the general idea.The central gear is threaded internally and runs in a ball race bearing.

Here you go.
These ballast piston tanks were found on www.rcboot.de
I have just received a 4"OD x 12"length x 3/8" wall thickness 6061 aluminum tube for my piston tank cylinder.This will have a capacity of 1500ml.I will gundrill through the length of the wall thickness for internal compression rods to compression fit a 13" length polycarbonate wtc on each end of the tank cylinder.There will also be extra gundrill bores for air relief and wiring chases.The drive motor will drive the piston rod with it having a threaded hollow-core shaft.This will fit in my Engel Gato.
I will post photos soon.
Giovanni

Giovanni,
Wow, great photos! and I see the threaded center (that is the area I need to learn to build). There are two relays that I will believe limit the fully extended and fully retracted piston by turning off the motor.

Thank you so much for finding these! I will keep looking as well. Does anyone have a plan or drawing that they are willing to share?

Peace and Cheers,
Tom

Very nice photos.

Looking at them, it occurs to me that piston tanks are always shown with the threaded rod retracted.

Is this to try and gloss over one of the major disadvantages of pistons tanks -a whacking great screwed rod taking up all your scarce internal space?!

I will get down off my "soap box" now but they are not the perfect system that seems to be a commonly held view. Oh and the internal pressurisation problem and the power failure that leaves your sub sunk. But they don't half control your sub well!

David,

I see your points and maybe I do have a misconception. My application is for a small sub and I thought a syringe type piston would offer enough ballast control, be compact, and allow static diving. I am certainly open to ideas. My wtc would have to stay 37mm OD x 250mm.
Any suggestions?

The ballast comparisons:
The piston tank is the most reliable ballast system for any boat, period. "Oh, but you'll run out of electric under water!" This is a scare tactic. Aside from signal loss, the controller has undervolt failsafe and there is a trimmer pot where you can even adjust the safety cutoff voltage if you really want to. Mine pops up with plenty of surface playtime left, and that's after an hour of normal running. This brings me to another point: electricity. The tank uses some electricity, but it's not that important because it's not constantly running the way your main motors are. The tank is not an electric hog the way some people like to portray it.
If someone's selling gas systems (which are completely viable systems) but they're knocking the piston tank or kits that employ it, ask them why Engel has sold over 30,000 piston tanks! And don't let them tell you it's because the Germans are short-sighted lemmings who can't let go of yesterday's technology. It's because they have enough of a fan base to support the manufacture of a superior, reliable turnkey system. You should also suspect anyone who attempts to abuse your lack of knowledge for commercial purposes.
Please don't think I'm down on gas. If you have a couple (or ten) gas boats, then why switch now? If you're already stocking propellant for your other boats and you already know the system then sure, stick with it. If you want to make an friend of a vendor, then buy their kit. If you only want to go with gas because it's cheaper, then build an RCABS. Maybe someday someone will actually build a commercial RCABS. Who knows, maybe reason and commerce could finally coexist.
Let me break down some negatives and positives to try to present some fairness.
Gas ballast negatives:
• There is no failsafe to keep you from diving when you do not have sufficient gas to surface again. If you have a gas failsafe and dive too deeply and lose signal, it goes off.
• Open surface (loose water) in the ballast tank means as the boat pitches forward, water rushes forward and pulls the bow down even more. This instability is lessened by the installation of baffles but it's always there.
• Airbrush propellant costs money.
• Filling the onboard resevoir every XXX number of dives is a pain.
• Counting the number of dives is a pain, and a risk, and if you don't get the onboard resevoir completely filled then your dive count is off anyway.
Gas ballast positives:
• Cheap
• Generally smaller WTC's
• Cool bubbles when you blow ballast
Piston tank positives:
• Your failsafe keeps you from diving if it's not safe to do so
• Your failsafe can go off as many times as you want and it resets when signal is regained, so there's no trip back to shore to refill the gas failsafe if you dive too deeply.
• If your receiver battery dies underwater, the BTS uses the main batteries (which are monitored for undervoltage) to empty the tank.
• No air is in the tank, so ballast water does not slosh forward and send you standing on your nose.
• You only change the batteries, and you get an hour of playtime per set.
• You dive as often as you want, without worrying about counting.
• The Engel tank in particular is a very high quality product. The selection of plastic materials and microswitches are all heavy duty. The construction leaves nothing to be desired. They dominate the market for this reason.
Piston tank negatives:
• Expensive
• Threaded rod travels in WTC using up space akwardly.
• Internal higher pressure but most subs have suffered no ill effects.
• Tank geometry is a fixed cylinder
• CG shifts a bit with a single tank
RCABS is in many ways the best of both worlds. It's cheap. It's all electric, so there are no gas hassles. You can run it with a BTS for undervolt and signal failsafe. The bladder can be arranged such that the center of gravity doesn't shift during filling.
Regards,
Giovanni

@ Richard - YES,YES, something like that! Would Nigel share his knowledge with me? I will build a larger unit if it means gaining the knowledge to tinker in the smaller range! Are there any plans out there? Would he sell me one of his? Or I can buy the parts from hime and assemble it myself or ????

@ Giovanni - I love your passion! In the U.S. there is a saying "6 of one, half a dozen of the other". In other words, they are the same and if your sub comes up and returns to you, that is a good ballast system. Thank you for explaining so well the pluses and minuses. I have seen with each system that the owners have considered the "What if" scenarios and built failsafes.

You guys are the best! Thank you for helping me understand and sharing information!

I am still on the hunt......

Richard,
Thank you again! I will do that now.
Cheers,
Tom

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.