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Author Topic: Air or Water ballast system for salt water use.  (Read 3053 times)

unbuiltnautilus

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Air or Water ballast system for salt water use.
« on: April 04, 2011, 04:12:25 PM »

I have just aquired a Darnell/Models by Design Type VII u-boat that has bounced around six previous owners ( including me! ) in the past few years, without getting underwater once, excluding the time it sunk by accident :-). It is divided into 3 watertight compartments, with the centre one reserved as a wet ballast tank, this compartment is currently sealed off completely i.e. no vent holes in the bottom of the boat.
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             Considering my local lake is salt water, which will restrict what I can do with the sub, I plan to alter the ballast to 'decks awash' and dive on the planes only. Hopefully a failsafe on the planes or ballast control channel will save me from going out of range.
The question is; Geared water pump, either pressurising the bolt down centre compartment or with an air reservoir, or 'old school' air pump (steam engine with buehler motor drive) with twin air bags using the centre tank as a reservoir?
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Re: Air or Water ballast system for salt water use.
« Reply #1 on: April 04, 2011, 04:25:44 PM »

You could use a diaphragm air pump instead of a piston based design, providing the pressure isn't too high (below 10psi).

I would say go for a Kavan gear pump, but it's got brass gears, and in salt water, I'm a bit cautious. The little orange geared pumps are plastic with stainless shafts, but are a bit slow- could use two in parallel I suppose, and they're only a fiver each off ebay.

The diaphragm pumps are plastic and rubber, nothing to corrode. Plus they move a lot of air very quickly provided you don't want high pressure.

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Re: Air or Water ballast system for salt water use.
« Reply #2 on: April 04, 2011, 04:28:49 PM »

Ooo, forgot to mention, there is also the Shurflo pump that OTW use in their dive modules. Haven't stripped one down, but I think they're mostly plastic, and they move water well. They won't make the pressure the geared pumps can though.

unbuiltnautilus

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Re: Air or Water ballast system for salt water use.
« Reply #3 on: April 04, 2011, 04:53:54 PM »

By diaphram pump, do you mean dismantled 'Woolworths' car tyre pump, as I have one of those out of its casing....?
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Re: Air or Water ballast system for salt water use.
« Reply #4 on: April 04, 2011, 05:09:53 PM »

No. I mean like this-

http://www.smartproducts.com/pumps.php

For a model like the Type VII which will have quite a big tank, this model would be right for reasonably quick dive times-

http://www.smartproducts.com/pumps_series_8000_air_pumps.php

You used to be able to get that model for peanuts at an experimenters rate, but they stopped that. However I know of a place in Germany that are selling surplus Thomas diaphragm pumps of equivalent sizes for a reasonable rate (25 euro), just don't have the link at this computer (can post later if you fancy trying that route).

Another  option is to use a pair of these- http://caswellplating.com/models/pumps.html

However they use small diaphragms and don't make the pressure of the larger pumps.

Another possibility- use a vented tank in conjunction with a centrifugal pump (Whale or Reich- about a tenner off ebay).

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Re: Air or Water ballast system for salt water use.
« Reply #5 on: April 04, 2011, 05:28:54 PM »

Just looked up the Thomas units, very impressive. If you have that info I would be most greatful. ( I have a pair of their smallest 4.5v units, possiblly purchased from Proops over 15 years ago and the quality is excellent, more suited to a Revell Type VII though!)
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Re: Air or Water ballast system for salt water use.
« Reply #6 on: April 04, 2011, 06:18:26 PM »

I have one of those. Have you ever tried them out? They shift more air than you think when run on a couple of lipos (7.4 volts). I wouldn't worry about over voltage, the motors cope just fine, and bear in mind you won't be running them continuously.

So, you might have all you need already. Try two in parallel you might be pleasantly surprised.

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Re: Air or Water ballast system for salt water use.
« Reply #7 on: April 05, 2011, 09:41:48 AM »

Will try that tonight, cheers... :-))
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Re: Air or Water ballast system for salt water use.
« Reply #8 on: April 05, 2011, 10:02:28 AM »

Here is that link-

http://www.respotec.de/shop/start.php?motoren_-_pumpen_-_ventile_-_luefter_pumpen.php

They do all kinds of interesting stuff for subs and other models, worth having a browse around.

They did have a 12 volt Thomas compressor, but they've clearly sold out, and only have the 24 volt model left. The seiko pump looks an interesting alternative, the spec says it can make about one atmosphere, although the flow rate at that pressure would probably be almost zero.

Ebay is another source, although some people charge silly money for these pumps as they're a shocking price from the manufacturer, but you might stumble upon a bargain.

Andy

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Re: Air or Water ballast system for salt water use.
« Reply #9 on: April 05, 2011, 11:49:08 AM »

Will have to brush up on my CSE grade 5 german though!
Cheers, Alan...
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Re: Air or Water ballast system for salt water use.
« Reply #10 on: April 05, 2011, 01:31:07 PM »

Foreign languages have never been my strong suit either. I find Google translator invaluable, although the pump data on that site is fairly easy to deduce.

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Re: Air or Water ballast system for salt water use.
« Reply #11 on: April 05, 2011, 07:20:00 PM »

Hi

I know AFC como do a 12v pump for a tenner, you cannot see it on their web site but give them a bell.

 :-)
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Re: Air or Water ballast system for salt water use.
« Reply #12 on: April 06, 2011, 09:17:18 AM »

Hi

I know AFC como do a 12v pump for a tenner, you cannot see it on their web site but give them a bell.

 :-)

I rusted one of those out on a surface boat many years ago when the water leaked up the shaft and seized up the armature. I have a peristaltic pump supplied by CML Racing sold as a fuel pump. Its low output, but reversable, I will see how long it takes to fill the tank. Not holding out much hope for it though...
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Re: Air or Water ballast system for salt water use.
« Reply #13 on: April 06, 2011, 09:54:47 AM »

What's the volume on a Darnell Type VII? I'd guesstimate 750-850ml.

Most of the small commercial peristaltics I've seen pump about 250-300ml a minute, so you'll be looking at dive times of about 2-3 minutes- yawn!

Didn't the little Thomas pumps work out?

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Re: Air or Water ballast system for salt water use.
« Reply #14 on: April 06, 2011, 10:52:22 AM »

What's the volume on a Darnell Type VII? I'd guesstimate 750-850ml.

Most of the small commercial peristaltics I've seen pump about 250-300ml a minute, so you'll be looking at dive times of about 2-3 minutes- yawn!

Didn't the little Thomas pumps work out?


Have not tried them yet, was struck down by the commoner garden 'too knackered to do anything' syndrome last night. RS Components have a diaphram pump at 41 plus VAT. Pretty potent at 3.8 litres a minute, but it is over 6 1/2" long. Must try my existing bits and pieces first though. Watch this space...


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Re: Air or Water ballast system for salt water use.
« Reply #15 on: April 06, 2011, 03:13:54 PM »

RS always seem to be an arm and a leg. Pump sounds big, the Smart products pump I have is a lot smaller and matches that flow rate plus some. It uses a high wind 12 volt 500 size motor.

You could still use the old converted tyre inflator pumps, but they're rather agricultural compared with the diaphragm pumps which are nicely balanced and smooth in operation.

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Re: Air or Water ballast system for salt water use.
« Reply #16 on: April 06, 2011, 05:59:48 PM »

I know these units are the way to go, but I am still tempted by the old OLD system using the steam engine, must concentrate more..... CONCENTRATE!
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Re: Air or Water ballast system for salt water use.
« Reply #17 on: April 06, 2011, 06:58:16 PM »

Sounds like you're wishing to build a boat that's a homage to earlier designs.

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Re: Air or Water ballast system for salt water use.
« Reply #18 on: April 07, 2011, 08:31:43 AM »

Sounds like you're wishing to build a boat that's a homage to earlier designs.



That does appeal to me, with modern equipment added where desireable. However, have tried the Thomas pumps; at 6v, using an SHG Large Centre Air Bag, 70 secs to fill, using two pumps, 45 secs. They are most impressive little units. I tried one in , one out, but will need a shut off valve in the line. Would you use these to inflate a bag or evacuate air out of a water tank, or as described, a reversable system.
The Boxxer Peristaltic pump took 35 secs to shift about 200ml of water, not so good. Might do for a set of hydraulic perescopes in my Alfa later though.

Or its old school!!!
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Re: Air or Water ballast system for salt water use.
« Reply #19 on: April 07, 2011, 12:33:39 PM »

What's the volume of a large SHG bag? Must be quite big for it to take that time to fill.

Are you familiar with the snort system used by Dave Merriman in the Caswell Sub Drivers? They use diaphragm pumps which draw air in from outside.

You need slight positive buoyancy for the system to work, but you want that anyway and it's ever so straightforward, and you have all you need already.

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Re: Air or Water ballast system for salt water use.
« Reply #20 on: April 07, 2011, 02:57:20 PM »

It has to be approaching 1 litre in volume. I am familiar with the system you suggest. I assume the air being drawn in would displace the water out of a sealed compartment, if so, would you then vent the tank to atmosphere to allow it to submerge 'naturally' or pump out the water?
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Re: Air or Water ballast system for salt water use.
« Reply #21 on: April 07, 2011, 03:07:47 PM »

Let it vent naturally. You need to make up a servo controlled valve. You can get solenoid versions but the valve orifice tends to be a bit small. A lightly modified tyre valve would work actually.

Rig both pumps so that they blow into the tank.

If you want to be really sharp, you could place a smaller trim tank inside the main ballast tank, and feed that with the perstaltic you have.  This could be a syringe with the displaced air compressing into one of the dry compartments, or it could be a baffled sealed tank. You could hover the boat with that system.

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Re: Air or Water ballast system for salt water use.
« Reply #22 on: April 07, 2011, 05:38:46 PM »

This type of thing?
As a valve, how about a pinch valve using a large bore piece of silicone tubing 5mm ID for example?

Excuse the slightly non-scale type VII image!
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Re: Air or Water ballast system for salt water use.
« Reply #23 on: April 07, 2011, 05:50:26 PM »

Okay, no vent holes in the bottom of the water tank, try again :-)

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Re: Air or Water ballast system for salt water use.
« Reply #24 on: April 07, 2011, 05:58:38 PM »

That's the idea. Not sure how the air pinch valve will work out in practice, they work great for water but it'll cost very little to try it out so you have nothing to lose except a few hours of your life.  :-))

Andy
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