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Old Oct 15, 2010, 03:21 AM
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Wtc sealing and piston ballast tanks

Hi all. I've built a WTC for my SCALE SHIPS 1/96 AKULA II, with ENGEL piston tank. The WTC is closed with o rings, nuts and washers, and aditional o rings are fitted on every rod of the WTC mounting. Shaft seal in an ENGEL one. After successfully passed the dry fittings checkings, went with WTC wet trials.
No leaks at the begining but, when operated the piston tank, problems arised. As I've been told about the increasing pressure inside the WTC when ballasting, keep it in the "loaded" position before closing WTC. Began the test and no leak at the very first moment but, when started a cycle of ballasting and deballasting, bubbles appeared through the shaft seal and one of the rods and, of course, water also appeared inside the WTC.
Any suggestion? I'll take and post pictures of it.
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Old Oct 15, 2010, 03:34 AM
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Originally Posted by u552 View Post
keep it in the "loaded" position before closing WTC.
Hi,

I totally disagree with closing the WTC with the dive tank in the loaded position, because when you vent the tank you start to suck you WTC below atmospheric pressure and you have a good change to suck water in your WTC as happens.

So please, empty your tank and close your WTC
Little Tip: Make a hole in your WTC with a tube on it and blow some air in by yourself no pump!!! after you closed the WTC and a cylinder can handle some pressure from the inside with out any problems.

You can have better bubbles leaving your WTC and solve that then see nothing and suck water in instead.

For the rest I find that you do a good job..

Regards,

Jan,
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Old Oct 15, 2010, 04:38 AM
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I dont know what to say other than you did not seal it well or mount your seals correctly. Yes, piston tank must be empty when you seal the WTC.
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Old Oct 15, 2010, 12:18 PM
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Thank you very much for the info. Here I send some pictures of the thing

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Description: Back plate of the WTC. Bubbles came out from the shaft and the nut "at two o clock" in the plate[/ATTACH]
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Old Oct 15, 2010, 12:28 PM
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These are general wieus of the WTC and how it sits on the sub. I've givcen her a coat of color after one of coachbuilder primer. It seems better you know.

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Description: General wiew from the bow

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Description: WTC mounted. You can see the batteries used , the magnet for the fore planes link and the On / off trigger

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Description: Installed in the sub, with rear linkages connected (rudders, rear planes and shaft
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Old Oct 16, 2010, 03:52 AM
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Hi,

I'm not sure but it seems that you have mount the shaft seal the wrong way, because the lips of the seal must be facing inwards the WTC and it seems that they are facing outwards?



Explanation; If its a spring loaded lip seal, the spring must be facing to the WTC dry side and as I see it now its facing to the wet side.

Concerning the bubbles by the bolts put some grease on the bolts and underlay rings and I think it will be cured.

Regards,

Jan,
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Last edited by Horseman; Oct 16, 2010 at 03:58 AM. Reason: Forgotten something.
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Old Oct 16, 2010, 08:20 AM
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Glups! Thank you ver y much, Hoseman, for your indication about the shaft seal. Yes, it's of the kind you say; I'll turn it to the other side. I've no indication about it. Regarding to the nuts, I'll put some silicone sealant over them. But, please, explain more detalied what you told me about blowing air inside the WTC. I ve schrader valver to mount in the WTC. I suppose you mean to blow through it when mounted.
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Old Oct 16, 2010, 09:00 AM
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I am pretty sure with a Simmering the spring must be on the wet side in a submarine. This is what Engel reccomend in their Lafayette kit instructions. But I dont think it make much difference either way.
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Old Oct 16, 2010, 09:25 AM
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Hi,

Glad I can help you. I know that some seals will work fine that way you have but in your case its maybe better to swap the seal the other way because the pressure inside your WTC will be higher than the water pressure outside the WTC. or you want to go deeper than 2 to 5 meters?

I have the Lafajette also and indeed the seal is facing outwards but I put it inwards.
I think its working better that way, maybe I'm wrong.
It also depends on the volume of the WTC and the volume of the dive-tank(s)

I do not know the volume of your WTC and the volume of your dive-tank but if they are the same you get a pressure of about 0.5 bar inside your WTC when the dive-tank is filled, so you can go 5 meters deep before the seal maybe starts to leak inside the WTC.
But if you go 5 meters deep you are in BIG trouble anyway..

Then I meant by: make a hole in your WTC with a tube on it and blow some air in by yourself.

First you put a brass tube trough one of the end caps of your WTC and on the outside of that tube you connect a silicon hose with a stop at the end.

When you have closed the WTC you blow some air in the WTC with your mouth to create a bit of over pressure in the WTC and closes the silicon hose.

On the next photo you can see the hose leaving my WTC from my Engel Gato.



Now you are able to observe if the WTC is sealed when you put it in the water, also if there is some minor leakage there is no real danger when you dive and rises again because you have a little air buffer now.

I mean: it will take more time before you lost that amount of air.

So when you blow your tanks (the dive-tank starts to suck air out of the WTC) and your WTC over pressure is decreasing, you still have overpressure in your WTC after the tank is emptied completely.

So there is still no danger to suck water in your WTC

I hope you understand now what I put down here.

Regards,

Jan,
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Last edited by Horseman; Oct 16, 2010 at 10:49 AM.
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Old Oct 16, 2010, 02:16 PM
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Thank you very much for your tips. My WTC is 55 cm long, 10 cm outer diamtre and 9,6 cm inner diamtere, with a volume of 829 cc. Ballast tank is a 650 cc TA ENGEL one, made on request.
Just back from the "shipyard" for another batch of tests, and problems are bigger and wort. The big mistake is my concept of sealing the end caps.
You see, as I don't have a lathe, made end cups with discs rounded with a drill, fixed together in such a way that there's no slot for the o ring. O ring works by being pressed between the edge of the tube an the outer plate of the end cap, as you can see in the pictures. Name: P1010014.jpg
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Description:

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Description:
This way the sealing effect is smaller and less effective. Will work for another kind of ballast system with no inner growing pressure.
So I'll have to make new end caps.
Regarding to the shaft seal, I've turned it with the spring facing inside; seems like it sit a little "tender" in the tube; Hoped won't get popped out when pressurized.
Anyway, thank you very much again for your aid. I'll keep you informed about the progress of the rebuild.

Regards, Juan Carlos.
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Old Oct 16, 2010, 05:06 PM
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1. With a piston type ballast tank, it's best to use O Rings for seals since these will seal in both directions.

2. When sealing your WTC prior to putting it in the water, position the piston as close to the mid point of travel as possible. This is the best compromise as far as pressure/vacuum is concerned. Putting a pressure port in the WTC isn't worth it since you'll never be able to pressurize it enough via lung pressure.

3. There's nothing wrong with your method of sealing the end caps as long as the end of the tube is clean, smooth, and straight. I've been doing that for several years with absolute success.

4. Use "acorn" nuts on your threaded rods which hold the end cap in place with an O ring and no washer. There's no way to seal the threads reliably. I'd be willing to bet this is where your water is getting in.

Hope this helps.

Skip Asay
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Old Oct 17, 2010, 09:57 AM
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Hi Skip,

There's no way to seal the threads reliably.

I can?? time after time 22 of them 14 in the main hatch and 6 in de secondary hatch.



The nuts with o-ring are nicer of-course.

I also agree with you Skip, that if the end of the PVC tube are clean and smooth the O-ring will work nice and secure, maybe the dimension of the used 0-ring are to small?

But Skip, I think you missed my point about the pressurising of the WTC and the main purpose of that. You don't need much pressure, the dive tank will do the rest.
The main goal are keeping a bit more pressure in the WTC than the outside pressure just a bit.

However I must tell, there are more solutions for one problem and we (modellers) are great to find more than one sulution for one problem so its hard to tell who is right or wrong.

If you ask ten Guys how to deal with this problem you can get nine different answers. perhaps ten.

So please don't start a discussion about who wrong or better than... maybe we are both or maybe not.

But Juan, no need to change the ballast system yet (my opinion)

Try what sounds best and do your own thing, because building (Subs or whatever) you must do that by yourself. We in Holland said; Its your party

Greetings,

Jan,
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Last edited by Horseman; Oct 17, 2010 at 10:19 AM.
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Old Oct 17, 2010, 11:17 AM
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mr horseman ,
Do you know who Skip Asay is?
If not do some research .
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Old Oct 17, 2010, 11:59 AM
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Originally Posted by Horseman View Post
Hi Skip,

There's no way to seal the threads reliably.

I can?? time after time 22 of them 14 in the main hatch and 6 in de secondary hatch.
Surely you have sealed the heads of the bolts holding the hatch lid down on the inside, so of course water wont find its way down there. The OP has free running threads.
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Old Oct 17, 2010, 12:40 PM
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Originally Posted by Horseman View Post

However I must tell, there are more solutions for one problem and we (modelers) are great to find more than one solution for one problem so its hard to tell who is right or wrong.

If you ask ten Guys how to deal with this problem you can get nine different answers. perhaps ten.

So please don't start a discussion about who wrong or better than... maybe we are both or maybe not.
Who Skip is I understand now, but the above phrase stays the same.

Hellomoto,

Surely you have sealed the heads of the bolts holding the hatch lid down on the inside, so of course water wont find its way down there. The OP has free running threads.


You and Skip have a point here I'm wrong sorry I did not see that.

I try only to help somebody and Skip also don't shoot me please.

Regards,

Jan.
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Last edited by Horseman; Oct 17, 2010 at 12:55 PM.
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