a little help understanding the OTW module....

[kielbasa]

Ok,
I get that it uses a pump to pump water in an out of one tube. I see in the glamour shots of the WTC, the blue intake/output tube comes from outside the cylinder, to a brass part, which I assume is a solenoid that acts as a valve. Then the blue tube goes to the pump and into the tank. Water goes in, pump is reversed, and then water goes out.

How does it overcome the pressure? I saw somewhere that there is a hole on the top of the bulkheads, that allows for air that is in the tank to escape into the rest of the cylinder (where the electronics are). I also see that there is a metal (brass??) part sticking into the tanks at a high and low point to turn off the pump when full or empty.

So, first, am I correct?

and B, isn't a hole in the top of the bulkhead bad? i get it the pump would be turned off before it fill completely? But what if the sub is at a bow up or bow down angle, wouldn't that allow the water to flow in- and let out the blue smoke?

Or am I wrong.....(definitely wouldn't be the first time......)
thanks mucho

[JWLaRue]

Hi Dave,

So..yes and no......

When first produced, the OTW dive modules did have a very small hole at the top, forward end of the ballast tank. If the sub took an extreme bow down angle it was possible to get a couple drops of water into the forward dry space. (It's a *very* small hole) But I've not seen water streaming into the dry space. The modules currently being produced do not by default include the hole, but OTW provides a partially drilled hole in the same location in the event that the customer wishes to open it up. I have both types of ballast tanks in my various OTW dive modules.

There's a trade-off involved here.

With the hole, the air in the ballast tank gets evenly distributed between the two dry spaces. Assuming that the ballast tank and the two dry spaces are all of equal length, the maximum resultant internal pressure when the ballast tank is full is about 1.5 bar....3 parts of sir into 2 parts of volume. (1 bar being atmospheric pressure and assumed to be the starting pressure of the entire dive module)

With no hole, the air in the ballast tank gets compressed in place. From a non-scientific visual observation of one of my dive modules, it looks like the ballast tank gets to about 60% full before the pump can no longer push water against the air pressure. This would result in something just over 2 bar of pressure.

The brass parts you see sticking into the ballast tank (through the forward ballast tank bulkhead) are water detection probes. There are two at the bottom (one is the common/negative and the other is the low water probe) and one high water probe at the top. When water in the tank provides a connection between the common/bottom probe and the high water probe at top it send a signal to the pump electronics to stop the pump and close the solenoid valve. Then when the bottom low water probe loses connectivity to the common probe (the tank is empty) it commands the pimp electronics to stop the pimp and close the solenoid valve.

...hopefully this makes sense?

-Jeff

p.s. Let me know the next time you can make it to one of our SubComEast FunRuns and I'll make sure that at least one of the subs I brings has an OTW dive module in it,

[kielbasa]

Thanks Jeff, I will do that, Looks to me (if its still the second Sunday) Feb 10 would be it. I'll check with the boss lady to see if I am available. Wold love to see one and poke around it a bit.

[JWLaRue]

That's correct....February 10th is our next run.

-Jeff

[KevinMC]

[snip]But what if the sub is at a bow up or bow down angle, wouldn't that allow the water to flow in- and let out the blue smoke?

Or am I wrong.....(definitely wouldn't be the first time......)

You're categorically wrong Dave! There's no blue smoke in electronics.

As an electronics professional I can assure you that electronic devices contain magic smoke, without which they will cease to operate. Everyone knows that!!!

[kielbasa]

Kevin, lol, you are correct, I just checked it on the wikipedia......

Jeff, planning on being in Shrewsberry tomorrow! see you then.

otherdave