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Author Topic: otw  (Read 1586 times)

Robin smith

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otw
« on: February 13, 2013, 08:09:03 AM »

my type 7c has always been a problem, difficult to balance and set up first dive and it is a problem there always seesm to be more water in the tank than orinally started with. I have fitted new pump and ceklaned probes and replaced balast controller. So dissapinted spends more time in bits under investigation. I dont think the pump is man enough for the job, pumps water in ok but does not pump out well. Is it back pressure of water outside the WTC? There are no leaks in the WTC have checked all thsi in my test tank. 
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Re: otw
« Reply #1 on: February 13, 2013, 11:46:42 AM »

The OTW system uses a centrifugal style pump with a slinger ring. According to the manufacturer, they can pump upto about one atmosphere, or about 15 psi.

That's enough to pump against a depth of over 30 feet, so that's enough of a safety margin in my book!

The OTW system displaces air into the dry areas as the tank fills with water. This pressurizes the cylinder slightly to a few psi (will vary but probably around 4-6psi), so if the tank is filling okay, that suggests the pump is working well enough. You say the WTC is fully watertight, but is the tank air tight? If air is escaping as you pressurize, then when it comes time to empty, you will be pulling a vacuum, and I'm not sure how well the pump works against a vacuum.

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Re: otw
« Reply #2 on: February 13, 2013, 05:25:20 PM »

Thank you so much for your reply. I have had the WTC out several times now and in my test tank when I select pump water in I can see no air bubbles from anywhere, the obvious places such as drive shaft seals and rubber boot areas are all fine. If there was a leak then I would expect to see air bubbles rising or clinging to the leak area and there is nothing. The pump used is a Shuflow 100 which I purchased back in may last year from Williamson Pumps Ltd. I dont think this pump is made any longer and obsolete. The one I have is what I call a wobble pump. I think the clearances and tolerances in the pump chamber dont make it the most efficient pump in the World it shifts water but I wonder if any back pressure gives it a problem. My immediatte thoughts are to upgrade to a better pump without blowing seal etc. That is if there is such a thing on the market. I must say in the test tank it seems to go better than when installed by what I can see by a visual indication of water in versa water out. The idea of the OTW WTC is fine but in my view the pump capability is not what it should be to maximise on the principle of operation.
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Re: otw
« Reply #3 on: February 13, 2013, 05:47:07 PM »

I've seen these modules in operation and the pump works efficiently from what I've seen. I don't think you'll improve on it with anything else.

The design of the OTW module takes into account the low pressure these pumps can make. The flow rate is listed as 1 gallon per minute, and appears to be fairly linear up to 15 psi when the pump stalls. At 7 psi the flow rate is halved.

Something is either wrong with the wtc, or the way you have installed it and set it up.

There is a limit to what can be diagnosed via a forum like this. It might be best if you can get someone experienced with this module to give it the once over, and check your installation. A modeller who goes to the Norwich club quite a bit, Dennis Pond has at least two of these modules, one in a Type XXIII and another in a Seehund. Perhaps he would be willing to give you a few tips if you could arrange to meet with him at Norwich. If you speak with Bob Dimmack he may be able to put you in touch.

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Re: otw
« Reply #4 on: February 13, 2013, 09:09:30 PM »

I have spoken to Dennis and know here he lives he has suggested I call in and see him. Unfortunately my wife is quite ill which resticts me quite a bit. I have a holiday home in Norfolk and pass thru where he lives I will try and arrange something.
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Re: otw
« Reply #5 on: February 13, 2013, 09:28:42 PM »

I see. I'm not sure what else to suggest. My experience of the OTW modules is limited to working on a couple of them, which is how I know what goes inside. They're not a cheap option, but seem to be well regarded by their owners- this is the first time I've seen anyone with major issues.

I guess with the system set-up the way it is, it's possible for a little bit of water to remain in the tank once emptied, but no more than an ounce or so.
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