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Author Topic: Robbe U47 Air Valve  (Read 4577 times)

irishcarguy

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Robbe U47 Air Valve
« on: February 17, 2012, 07:47:39 PM »

I getting to a point on my rear bulkhead to add the air valve. I'm  using a Engel Piston tank so they water line coming out at the 12 O"Clock point (too late to change) and there's the rudder and rear dive plane connections along with the prop shafts. It it really necessary to add the air valve? I guess i could attach on the front bulkhead.
Thoughts Please
john
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Mick B.

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Re: Robbe U47 Air Valve
« Reply #1 on: February 17, 2012, 08:27:17 PM »

You can pressurize the cylinder using the piston tank. However you might want to consider some form of tap off in case you pull a vacuum inside, and need to release that to separate the hull.

Sub driver

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Re: Robbe U47 Air Valve
« Reply #2 on: February 17, 2012, 09:20:05 PM »

Hi.
Not too sure what you mean by using an engel tank with the water line comming out in the 12 o'clock position ?

Do you mean the inlet for the Engle tank is in the 12 o'clock position ??.

If so its quite a radical position for it if it is, as the inlet may well be above the water line when the model is fully surfaced, the best place for it is at the bottom of the rear bulk head .i.e 6 o'clock position it is then always under water, when fully emptied / surfaced, also remember the engel tank is just a high tech syringe.

But... I would fit the air valve for a number of reasons one of which is mentioned by sub culture.

Regards Sub.
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REDDEVIL

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Re: Robbe U47 Air Valve
« Reply #3 on: February 17, 2012, 09:29:32 PM »

ENGEL instructions state that piston water inlet is to be at "12 o'clock" position. Mine is mounted that way on my AKULA II and no problem at all. Regarding pressure build up inside the watertight compartment when filling the tank, my WTC is closed with o rings and external nuts pressing them against tube edges. No leaks. And ENGEL recommends to close water tight compartment with tank in "empty" position to avoid vaccum when deballasting and possible leaks due to it. Hope this hepls.
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REDDEVIL

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Re: Robbe U47 Air Valve
« Reply #4 on: February 17, 2012, 09:32:35 PM »

One more thing: Water intake in the tank is at "12 o'clock", but the intake at rear bulkhead is at "6 o'clock". Water tube is "s" shaped from tank intake to the rear bulkhead and external intake.
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REDDEVIL

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Re: Robbe U47 Air Valve
« Reply #5 on: February 17, 2012, 09:39:44 PM »

Here are a couple of pic. In the first one you can see the water tube coming out the tank. In the second one you can see the external intake right under the prop shaft.



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Sub driver

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Re: Robbe U47 Air Valve
« Reply #6 on: February 17, 2012, 09:40:13 PM »

Red Devil.

EXACTLY my point that the INLET should be at the 6 O'clock position. Not the tank position

If it is there on his build then the fitment of the air valve can be in the upper part of the bulkhead where it is shown on the plans.

My V11C and XX1 and Akula all have the inlets in this position.

Regards Sub.
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irishcarguy

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Re: Robbe U47 Air Valve
« Reply #7 on: February 17, 2012, 10:16:00 PM »

Thanks for the advice but to clarify the six O'clock position on the rear bulkhead would be well below the water line so in my mind I don't think in my mind this as a problem Would do ya'll think?
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Mick B.

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Re: Robbe U47 Air Valve
« Reply #8 on: February 17, 2012, 11:10:45 PM »

I have an air valve (a tire valve one) mounted at fore bulkhead upper part. What use to do is blow it, immediatly after closing the WTC, to equalize pressure inside and outside the WTC. In this picture it wasn't fitted yet, but it's now in this bulkhead upper part.

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Sub driver

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Re: Robbe U47 Air Valve
« Reply #9 on: February 18, 2012, 02:26:55 AM »

Red devil.  When you blow into the valve on the closed wtc you are increasing pressure in the wtc not equalising it. Its already equalised inside and out when you bolt it up. The idea of blowing into the valve is to give it more pressure inside than out so when you place it into the water any leaks in the wtc would be evident by a stream of air bubbles.   20........if the the inlet to the water for the engle tank is located at the bottom of the rear bulkhead thats ok.   Regards sub.
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Subculture

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Re: Robbe U47 Air Valve
« Reply #10 on: February 18, 2012, 10:16:56 AM »

I think he meant that once buttoned up, he depresses the pin to let out any air that is compressed inside once the end caps are fastened.

REDDEVIL

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Re: Robbe U47 Air Valve
« Reply #11 on: February 18, 2012, 12:58:48 PM »

Yes, I do what Subculture says to equalize inner and outer pressure, because when ballasting with an ENGEL piston tank, inner pressure rises a lot. I checked the WTC for leaks at my testing tub filling the tank and pushing the WTC to the bottom. Till this very moment (knock on wood), no leaks.
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Mankster

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Re: Robbe U47 Air Valve
« Reply #12 on: February 18, 2012, 02:19:12 PM »

I just use a brass tube and silicone hose with a stopper in all my boats. You can have any lenth of silicone tube so you bring it out somewhere more accessible. A 3mm brass tube is easy to fit anywhere compared to a schreder type valve.

That WTC design looks familiar  %)

Subculture

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Re: Robbe U47 Air Valve
« Reply #13 on: February 18, 2012, 02:43:55 PM »

I've been wondering what the little servo and microswitch is being used for

REDDEVIL

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Re: Robbe U47 Air Valve
« Reply #14 on: February 18, 2012, 10:07:59 PM »

To switch an ADC on and off. Removed it later because, don't know why, didn't worked properly. The ADC was connected to the fore planes.
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REDDEVIL

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Re: Robbe U47 Air Valve
« Reply #15 on: February 18, 2012, 10:12:56 PM »

Yes Mankster, it's yours, and works incredibly well  :-)) Thank you very much for your thread about. You can see her sailing in you tube here: http://www.youtube.com/watch?v=B0nx0ldGNPs&feature=g-upl&context=G21018eaAUAAAAAAAAAA
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Re: Robbe U47 Air Valve
« Reply #16 on: February 18, 2012, 10:50:25 PM »

To switch an ADC on and off. Removed it later because, don't know why, didn't worked properly. The ADC was connected to the fore planes.

Ah right, I think I spy the ADC tucked underneath the servos. It should be mounted as far forward as you can get it. Also I wonder if the changing pressure inside the WTC due to the piston tank had some effect?

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Re: Robbe U47 Air Valve
« Reply #17 on: February 19, 2012, 12:31:00 AM »

Ahh thought that design of wtc looked familiar.  Nice vid too well done.
......May you always surface the right way up.....
Regards sub.
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REDDEVIL

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Re: Robbe U47 Air Valve
« Reply #18 on: February 19, 2012, 12:58:07 PM »

May be the problem was that the ADC was mounted astern, but the problems arose with the WTC open. The sub is a little bit tender surfaced, but very stable underwater, so no problem with transverse stability and always surface the right side up... till this very moment.
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Subculture

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Re: Robbe U47 Air Valve
« Reply #19 on: February 19, 2012, 02:14:39 PM »

I remember Manksters Akula had some problems with stability on its first outing. Needed some more foam up top to make it stable. An idea passed on to me by Ron Perrott was to add free flooding tanks above the waterline. The trick with these is to make the holes on the bottom of the tank small, so they take a little time to fill. That way if the boat rocks and rolls on the surface the tanks won't fill, therefore acting like buoyancy tanks, and help keep the boat stable, but when you fill the tank to dive, they will flood, thus minimising displacement required.

You would need to experiment with the hole size depending on how long your tank takes to fill, but this sounds like a very neat way to dial in a bit more stability if it's required, whilst keeping the ballast tank volumes small(er).

If you want to try a practical experiment, get a small drinks bottle, drill a small hole in the top, say 1mm, and a larger hole in the bottom, maybe 3-4mm, try pushing the bottle underwater, and you'll notice that it has a strong upthrust, and very little water is taken in.

REDDEVIL

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Re: Robbe U47 Air Valve
« Reply #20 on: February 19, 2012, 07:57:48 PM »

As I said, she's a little tender surfaced. This is more evident at high speed and, in my case, when turning to port. At the same speed and turning to starboard, there's no list. So I think it's more a question of weight balance. By the way, my ballast tank is 650 and takes 12 seconds to completely get filled. If don't wrong, Mankster tank was 500 cc, and I kept my WTC almost the same length than Makster one. Thus, inner pressure build up has to be a little bit bigger. Backing to ballast and stability, distance from WTC to hulll is only 1 centimetre, so ballast tank is as lower has can be and almost completely under surfaced waterline. And these all keeping a quite real surfaced waterline.
Thank you for the ideas.
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Subculture

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Re: Robbe U47 Air Valve
« Reply #21 on: February 19, 2012, 08:26:47 PM »

That sounds like it could be torque roll from the prop.

REDDEVIL

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Re: Robbe U47 Air Valve
« Reply #22 on: February 19, 2012, 09:59:35 PM »

Yep, I've thought about, cause prop's left handed.
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