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[treeboa]

ok new to this subject, done a lot of looking around the web for ideas, i have a darnell hull with twin wtc`s ( boxes)
so first pic is the pinch valve, operated off a cam i have made thats fitted below at X servo horn, i mounted the cam below the horn as i feel it will be less likely to flex


the pump is something i pulled out of a 12v car tyre pump, only issues i had was the inlet was a hole on the head with a valve below it, i had to drill it out slightly and add a length of brass tube,  ( the thinner tube is soldered into a slightly wider one because of available space on the head)  also it has a spring operated one way valve on the outlet




right now down to the contraption working, the cam one way dumps pressure from a receiver back to the bag, the pump pulls via the bag and back into the receiver, its not super fast deflating the bag but my thoughts are it will allow me more control on it submerging
 

so have i got this right or am i missing something obvious 
 

[Subculture]

That's the first time I've seen a pinch valve used in a compressed air system, they're usually used for water pump systems. For air systems a modified tyre valve is usually pressed into service.

[Andy_k]

this might help

http://roguesubworks.com/downloads/diy-rcab.pdf

[treeboa]

thanks guys, however the parts i have are two darnell wtc`s ( boxes), an air bag  and  a fiberglass air receiver, this means im not using the wtc`s as the pressure receiver with the associated risks of damp air and electrics, with this setup i thought by keeping any compressed air separate i would lessen the chance of air loss through seals, the pinch valve i have made the `seat` adjustable so i can have a controlled leak which in the event of radio or battery failure i hope will act as a back up that will surface the sub


as a separate issue. i notice on wtc`s that use external batteries they have a pair of battery connection posts, are these available - had a look around the web but cant find them

[Patrick Henry]

I find a couple of brass bolts does the trick....



Rich

[treeboa]

thanks rich, i will do that then 

[Davy1]

You've done an interesting update on the original Darnell system.

How do you prevent the bag bursting?

(I think the original Darnell steam engine just ran out of puff!)

Personally, I prefer to pump water (it seems easier somehow) and I am not keen on bags because of them popping. But I think you are well on your way with your system.

David

[treeboa]

the way i worked with it, if you look at the second piccy you will see part of the air tank, i have bonded a tyre valve into it, what i did/do was work with the bag deflated, i have the air tube from the orig compressor, turning the cam to the dump position i then inflate the bag by attaching the air tube and blowing into the receiver which in turn inflates the bag, i can then gauge how much airs in the bag, the pump then sucks from the bag, opening the pinch valve means it can then only re inflate the bag from the pressure contained in the receiver, this hopefully is enough to surface the boat, max depth i will be using it on is 3 foot

as a side line, i have had the bag inflated for two days, then deflated into the reciver for the same time, seems im loosing no air 

[Subculture]

A lot of people replaced the electric motor on the compressor with something smaller and less thirsty, like a low draw 400 size motor.

The RCABS system mentioned in an earlier post, operates on a similar principle, albeit minus a bespoke reservoir.

It's on a smaller scale, which was made possible by the commercial availability of small inexpensive air pumps. These pumps simply weren't readily available until about ten years ago, so if you wanted one, you had to make it yourself which required workshop facilities, or have it made bespoke- which meant a lot of £££. Craycraft used to make a couple of small piston based pumps, which they used in their range of dive modules back in the day. Thirteen years ago, when Brian shut up shop, they cost about eighty quid.

Unsurprisingly, constructors of ballast systems for smaller boats leaned towards  water pumps or gas (propel, freon etc.) which could be constructed from readily available parts without requiring precision tooling.

[Davy1]

Yes, I see.

So the bag can't burst because their is only enough air in the reservoir.

Neat!

[treeboa]

Subculture  - i will look into that one as its a 540 at the moment, does take some power from the batts, however im thinking of it having its own battery, that way its not taking power from the drive motors or more importantly if shes down the receiver/servos


davy1  -- yeah that way my thinking, my only worry is the depth pressure at three foot does not allow the bag to inflate enough to bring the boat up, place i will sail it is three foot max so if this does happen i will have the chance to get it back , i may for the first few static  dives try it with a float attached to a cord, i can pull it back up then if all else fails

[Subculture]

1.5psi at 3 feet depth- I don't think you'll have any problems to be honest. It's not a bad idea to trim your boat so that it is just slightly buoyant with bag fully deflated if you want to maintain trim. If you leave residual air in the bag, it will compress slightly as you dive.

Sparkfun do some nice diaphragm pumps that will be a lot less thirsty than the version you have-

http://proto-pic.co.uk/12v-vacuum-pump/

[treeboa]

now that little pump could be a better idea - cheers for the link 

[bbdave]

Is that one of those them there pumps i could use for snort i.e. it'll deal with water to?

Dave

[Subculture]

Indeed- it's diaphragm based, so suitable for snorting. However it's a larger model suitable for medium sized models and upwards.