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Author Topic: Salt Water Darnell U37  (Read 54913 times)

U-33

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Re: Salt Water Darnell U37
« Reply #125 on: October 17, 2013, 09:28:41 am »

Looks like it might be a drain on the system.


Oh Andy, please...is that the best you can do? Mind you, it is early in the day... ;D
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #126 on: October 17, 2013, 09:38:44 am »

What function does the third hose on the left do? I have an 'in' and an 'out' only, reversing depending on motor direction. Substitute the air reservoir shown for my RC compartment and it is pretty much the same system.
Drain jokes, shame on you ok2
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Subculture

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Re: Salt Water Darnell U37
« Reply #127 on: October 17, 2013, 09:48:16 am »

I think that must be for initially priming the system.

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Re: Salt Water Darnell U37
« Reply #128 on: October 17, 2013, 10:40:19 am »

I have looked up the USE engines, they are designed to be stacked, making two, three or even four cylinder engines. I assume this is a take off for that connection. Fitted with a one way valve here they could indeed be primed through this pipe.
How about stacking a couple of these units to increase volume of air to the bag? As long as the motor could drive the twin cylinders?
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grendel

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Re: Salt Water Darnell U37
« Reply #129 on: October 17, 2013, 11:19:40 am »

I was referring more to the backdrop of the picture. ;)
Thats a system on a drain though!
Grendel
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Re: Salt Water Darnell U37
« Reply #130 on: October 17, 2013, 01:15:05 pm »

Thats a system on a drain though!
Grendel

Good point, well made.
Bad joke, well ruined :-))
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Re: Salt Water Darnell U37
« Reply #131 on: October 17, 2013, 01:37:26 pm »

Personally I wouldn't persist with this pump, becuase you can get something much better for under a score. They were considered superceded decades ago, back then modellers replaced them with the tyre inflator pumps- not that great either, but considered a step-up from the USE, and the best you could do unless you had the tools and ability to make a pump yourself or adapt an old glowplug or diesel engine. I've only ever seen one working Darnell boat with a USE, and that had been heavily reworked by the owner because in his words" it had a bore like a map of the Himalayas!"

I appreciate you are trying to make a bit of a working time capsule, but in some instances, I think nostalgia is a little overrated. Your call.

http://www.technobotsonline.com/12v-vacuum-pump.html

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Re: Salt Water Darnell U37
« Reply #132 on: October 17, 2013, 02:02:34 pm »

Nostalgia is giving me a 120 sec dive time, as long as I leave the hatches open to atmosphere, I want a crash dive!
I assume these are one way pumps, I have some tiny diaphram pumps with servo motors driving them, very effective but slow, also not reversible.  Those suggested certainly look more suitable. May consider two, one up, one down, with suitable one way valves if needed.
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #133 on: October 17, 2013, 02:37:28 pm »

Well you know what they say...'If in doubt, order it.'
Two on the way from Technobots. Thank you :-))
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Re: Salt Water Darnell U37
« Reply #134 on: October 17, 2013, 05:45:16 pm »

Good stuff. They're excellent pumps, and move a lot of air for their size, I think you'll be impressed when you try one out. They also make pretty good pressure, certainly much better than smaller models of diaphragm pumps.

You won't need any check/one way valves with these, they have the valves already built in, but you are quite correct, you can only pump in one direction with these.

The best way to set up the bag system is to inflate the bag before putting the boat in the water, then use the pump to collapse the bag, by sucking the air out, and storing it in either the box, or a separate bottle/tank. Do mind the pressure if you go for the former, as the forces ratchet up very quickly, and boxes are rather 'soft' when it comes to that kind of thing.

To come up just release a servo controlled valve or a solenoid air valve- a fail safe system (well as near as you can get).

The main snag with a compressed air system like this, is that it is impossible to trim for different water densities unless you leave some air in the bag, which of course is squishy, and will compress as you dive deeper. I think this is one of the main reasons modellers moved away from this system.

Some modellers in Germany use compressed air systems for the main ballast tank with smaller piston tanks for trim usually amounting to about 1-2% of the boats overall displacement. These boats offer the advantages of compressed air (e.g. minimal effort to surface and fast evacuation of ballast tank) with the benefits of fine trimming from the piston tanks.

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Re: Salt Water Darnell U37
« Reply #135 on: October 17, 2013, 05:55:57 pm »

Good to know about the installed one way valves. I have just had a very interesting and infuriating brainstorming session with one of the Display teams Johns. Between us ( mostly him! ) we have two systems to look at. Bearing in mind that we did not know about the non-return valves fitted in the pump at the time :-) . A system as described above, roughly (!), using one pinch valve and one pump, and a system using two pinch valves, one pump, but using the pump to both dive and surface.
My brain will be exploding very soon now.
This does leave me with one spare vacuum pump, good for experimenting with, and two SEL Steam Launch engines. Which seem to be at least a bit collectable, so tart em up and flog em both, pays for the vacuum pumps methinks :-))
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Re: Salt Water Darnell U37
« Reply #136 on: October 18, 2013, 08:18:03 am »

To answer an earlier question, I don't actually know what all the ports do on the USE engines. I simply blocked the ones off that stopped it working! Interesting what you say about the ability to connect them all together.

I am still puzzled about the problems you have had with the engine pressurising the WTC. I can only conclude that your engine is the "worse for wear" and hence best binned!

The example I have seems OK and I will try to get the original Darnell system working. "Grahams's Dad's Darnell is that kind of project.

However any problems with it and I confess that I will revert to my current "norm" ballast system.  A home made piston tank proportionally controlled by AMS software. I can knock these out very easily and cheaply now and those of you who went to Norwich this year will have seen these systems in my R class and Resurgam.

So best to scrap your USE engine , I was hoping to save you some time and trouble but I can see that like any good Model Submariner you thrive on challenges! It is probably worth pointing out that Internet advice is very cheap but the reality can be expensive.

Good luck with developing your system.

David
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Re: Salt Water Darnell U37
« Reply #137 on: October 18, 2013, 11:37:18 am »

Oscillating steam engines are very simple with just two ports, an inlet and exhaust. The conrod is fixed to the piston, and the cylinder oscillates on a pivot. You will have a single inlet to the cylinder, and as the cylinder moves back and forth that hole aligns with the inlet or exhaust port. As this is a sliding fit, you do get some leakage past the ports, and this will get worse as the engine wears.

You can lap the surfaces to improve this, but in all fairness as far as using these things for a compressor, it's putting lipstick on a pig.

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Re: Salt Water Darnell U37
« Reply #138 on: October 18, 2013, 11:51:48 am »

but in all fairness as far as using these things for a compressor, it's putting lipstick on a pig.

Surely you could just put a bag over its head?
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Re: Salt Water Darnell U37
« Reply #139 on: October 18, 2013, 01:50:21 pm »

You could indeed.

As an aside, the pump Brian Cornelius incorporated in the craycraft modules back in the day were oscillating, however they featured miniature plate valves located in the top of the cylinder heads. You could do a similar thing by plugging up the original ports, drilling a hole in the top of the cylinder, and plumbing in a pair of one way valves, but it won't be terribly efficient. The diaphragm pumps you can get now just weren't available until a few years ago, and their introduction made life a lot easier, as they're largely maintenance free, low reciprocating mass, meaning less vibration and thus fairly quiet in operation.

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Re: Salt Water Darnell U37
« Reply #140 on: October 18, 2013, 01:52:15 pm »

Surely you could just put a bag over its head?


We don't need to know about your other "interests", Alan, thank you very much....  8)
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Rich

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Re: Salt Water Darnell U37
« Reply #141 on: October 18, 2013, 02:14:42 pm »

Surely you could just put a bag over its head?


We don't need to know about your other "interests", Alan, thank you very much....  8)

Everyone should have a hobby, sometimes more than one....

Anyway, I assume these vacuum pumps would be equally capable of vacating the air from an acrylic tube, allowing water in from below, as well as inflating a bladder system?
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Re: Salt Water Darnell U37
« Reply #142 on: October 18, 2013, 04:57:21 pm »

Yes, they would work fine in that application, also unlike piston designs, they can quite happily live with ingesting a bit of water

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Re: Salt Water Darnell U37
« Reply #143 on: October 21, 2013, 09:28:54 am »

Hi Subculture

Do you have any personal experience of using these vacuum pumps in a working model submarine?

Many thanks Andy,

David
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Re: Salt Water Darnell U37
« Reply #144 on: October 21, 2013, 10:23:14 am »

I've used a virtually identical model in my Seehund. Was more than a match for the original piston compressor, and much smoother. Could have got away with a much smaller model of pump actually, but you can always slow the pump down.

The version I have is made by Smart products called the SP8000. They're not readily available (I got mine for a special price for trialling) and quite expensive if purchased at list price- the ones I linked to at technobots are much better value, and pretty much identical in terms of spec.

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Re: Salt Water Darnell U37
« Reply #145 on: October 22, 2013, 05:48:22 pm »

Bag or tank, this is my conundrum...or something like that anyway. The acrylic tank has a lower volume than the bag, so will support less. However it can be used with a reversable water pump or the vacuum pump, either blowing or sucking. The air bag can use one or two vacuum pumps, either reversable in and out, or transferred into a rigid tank and vented back to surface. The reversable option could burst the bag and will no doubt need a pressure switch in the system, them vacuum pumps are most excellent, cheers for the recommendation :-)) .
Nothing like having too many options....
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Re: Salt Water Darnell U37
« Reply #146 on: October 22, 2013, 06:19:46 pm »

If you're going to have the tank completely empty or completely full, why not use the hull itself as the tank, and glass in a top cover. this will make full use of the boats beam, giving you oddles of volume.

It wouldn't suit a pressurized tank as the tank wouldn't be rigid enough, but fine for the sort of system you have in mind.

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Re: Salt Water Darnell U37
« Reply #147 on: October 23, 2013, 11:22:17 am »

A case of a 'can't see the wood for the trees' moment. The centre compartment was originally a sealed tank, I took it out!
Good plan :-))
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Re: Salt Water Darnell U37
« Reply #148 on: October 23, 2013, 01:36:11 pm »

If you're going to have a fixed tank, with a recirculating air system, you will need to ensure there is no, or at least minimal chance of sucking water into the pump. That's probably the sole advantage of using a bag, you don't need that additional complication.

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Re: Salt Water Darnell U37
« Reply #149 on: November 01, 2013, 09:22:31 am »

Quick question? What should I expect to be an approximate ratio of volumes between air receiver tank and either air bag or water tank? I have tried fairly small reservoirs and the vacuum pump is giving up at about half deflation.  am I looking at a reservoir of similar size to the ballast tank? I am hoping not to use the RC compartment as an air reservoir at the moment.
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