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WTC FOR AKULA II

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Re: WTC FOR AKULA II

Postby JWLaRue » Mon Oct 18, 2010 12:04 pm

Skip Asay wrote:The net result is the same.

...like I said: similar.

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Re: WTC FOR AKULA II

Postby Sub culture » Mon Oct 18, 2010 12:19 pm

Just noticed I slipped up- you provided the dimensions of your cylinder already. So it looks like you will be running at about 4psi (0.27 bar) with the tank fully flooded. Might be pushing it a bit.

The simplest way to avoid leaks on rods is to run them external to the cylinder. It's not always possible owing to space restriction, but where it is, it elminates the possibility of more seals to leak.

The knurled thumbscrews shown by Jeff are very nice, but you can't make them unless you have access to a lathe. If you can obtain brass wingnuts, you can solder on a capped piece of tube to each one to seal off the thread from outside. These provide a nice way of fixing the endcaps without needing a box spanner. If you run the rods external, you don't need to bother capping them off.
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Re: WTC FOR AKULA II

Postby U552 » Tue Oct 19, 2010 2:01 am

You all are right. I've compared pictures of my WTC with Ramesh one, and mine is a little bit "crowdy" inside, because length is more or less the same, but I'm using a 650 CC tank (bigger tank and longer rod). The reason for this was the problems he had with achieveing a correct waterline. I though that with a bigger tank the problem will be solved, but the problem of pressure arose. My cylinder is 55 cm long, 10 cm OD and 9,6 cm ID, which means a net internal volume of 3.979 CC, but volume of all the fittigns is to be substracted to get remaining space to hold extra pressure, so the result is: Too many people inside for that tank (something similar to Marx brothers cabin).
Now there are no leak through the shaft with spring facing inwards, and I've applied sealing sylicon to nuts in the rear end cap. Fore cap is fitted with rubber tube inside and o rings outside to watertight threads on the rods. It's all working, but still leaking through rubber joint. You can see all these in attached pictures. Solution, as you have suggested, increase cylinder volume. There's room enough to fix a piece of tube forward which can give some 240 CC extra void space. Let's fit and check again.
Stay tuned for more rock n' roll.

Juan Carlos.


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Image
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Re: WTC FOR AKULA II

Postby Wheelerdealer » Tue Oct 19, 2010 4:38 am

Where exacly is it leaking from? The 4 nuts with the Oring on the outside or the main Oring for the endcaps?
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Re: WTC FOR AKULA II

Postby U552 » Tue Oct 19, 2010 6:48 am

There are 6 nuts because I thought that will be better for waterthight closure due to tube diametre. They're not leaking now. And it's not an O ring what seals end caps, it's a sheet of rubber placed between outer and inner discs of end caps. Now it's leaking through the edge of the tube and the rubber seal.
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Re: WTC FOR AKULA II

Postby Skip Asay » Tue Oct 19, 2010 10:10 am

I suggest that you go back to using an O-ring. The reason for this is that an O-ring, since it's circular, yields much higher pressure over a much smaller area than a flat sheet, thus sealing better. Of course, an awful lot depends on having clean, smooth surfaces for the O-ring to seal against. This is exactly how my WTC is sealed.

On a previous post, you stated that you don't have a lathe so I must assume that the end of your tube was cut with a saw. This will not yield the smoothest surface so I suggest you lay a piece of 220-360 grit wet or dry sandpaper on your bench, add some soapy water, and then rotate the end of the tube until all low spots are gone.

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Re: WTC FOR AKULA II

Postby Wheelerdealer » Tue Oct 19, 2010 11:17 am

Agreed, you need to use an Oring really when your pressurising the the WTC. I guess you cant tighten the nuts down any tighter to compress your exisiting rubber seal anymore?
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Re: WTC FOR AKULA II

Postby U552 » Tue Oct 19, 2010 4:47 pm

Yes, I thighten nuts as much as possible, with o rings under whasers, but seems that the tube size is a little bit small and will need to increase it with the suplementary piece of tube. There's room enough in the fore part to do it. This way the excess of presure could be holded by the closing seals. What's the length of tube you used in your AKULA? Mine is 55 cm, 10 cm OD and 9,6 cm ID.
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Re: WTC FOR AKULA II

Postby Albion » Tue Oct 19, 2010 7:30 pm

U552 wrote:Yes, I thighten nuts as much as possible, with o rings under whasers, but seems that the tube size is a little bit small and will need to increase it with the suplementary piece of tube. There's room enough in the fore part to do it. This way the excess of presure could be holded by the closing seals. What's the length of tube you used in your AKULA? Mine is 55 cm, 10 cm OD and 9,6 cm ID.


As others have said I O rings work much better. When an o ring is placed under pressure it deforms and squezes tigher into its groove, making a better seal. This is why o rings should always be lubricated (with some minor exceptions), so that they can slide and squeeze easily in their grooves.

In engineering, with large surfaces to be joined, you can replace large areas of gasket face with only a very small o ring.
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Re: WTC FOR AKULA II

Postby U552 » Wed Oct 20, 2010 4:00 am

Well understood. I didn't cut the tube, but the edge is not as flat as could be. As I have adequate wet sand paper, will do what Skip says and also change again to O rings. But keep in mind that O ring is between edge of tube and end cap plate, as I can't make a grove precisely. Anyway, I'm going to have a lot of fun making all these checks and trials, which is one of my targets in this hobby, so everything is right.
I'll keep you informed and thank you again for all you aid.
Juan Carlos.
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Re: WTC FOR AKULA II

Postby Sub culture » Wed Oct 20, 2010 10:15 am

Axial compression is fine, and easier to machine than radial compression.
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Re: WTC FOR AKULA II

Postby U552 » Fri Oct 22, 2010 2:38 am

So the O ring will seal by being pressed axily, instead of allocated inside the tube. Anyway, you can see the difference between rubber sheet gasket and O ring in pics attached to my previous posts. I think the problem is that tube is too small for piston tank size. If you compare mine with Ramesh, can clearly see that mine is much more crowdy, thus letting not free space enough to deal with extra pressure. I think that before changing gaskets again will arrange a check with the extra chamber at the fore part of the WTC.

Image

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Re: WTC FOR AKULA II

Postby Albion » Sun Oct 24, 2010 9:00 am

Sub culture wrote:Axial compression is fine, and easier to machine than radial compression.

so long as you have a groove, i think the plan here is to axially compress it, which is still a gasket not an oring really
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Re: WTC FOR AKULA II

Postby U552 » Sun Oct 24, 2010 5:24 pm

I've done the smoothering of tube edges and added the extra piece of tube forward. Also applied silicone sealant in read end cap nuts. Better sealing and almost no leaks. Fore end cap is sealed with o rings under washers and with rubber tube on the inner part of every rod. Have to make final checks yet but looks nicely promising. Also performed a floating trial with the wtc mounted in the hull. It sits barely in the real waterline deballasted, and with deck one inch under water fully ballasted, with part of the tower up. Seems a good starting point to final trimming. I'll take and post more pics.

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