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Author Topic: Welman build  (Read 16930 times)

bbdave

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Re: Welman build
« Reply #75 on: August 14, 2013, 08:06:50 am »

Cheers chaps where can I buy just a few o rings as the place I was looking has a minimum 10 quid order I may aswell buy the end caps ready made if that's the case plus I don't need over 100 of the things!


Dave
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Davy1

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Re: Welman build
« Reply #76 on: August 14, 2013, 08:27:02 am »

I have found these people to be very good:
http://simplybearings.co.uk/shop/index.html
Good delivery etc. I am told that you can buy O rings cheaper but they are very convenient and reliable. (Driving down to the shops can cost you a bit anyway.)
 
David
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bbdave

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Re: Welman build
« Reply #77 on: August 14, 2013, 01:40:38 pm »

Thanks that's better i'll have a think it still works out about 7 quid but I do fancy making the end caps .

Dave
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Subculture

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Re: Welman build
« Reply #78 on: August 14, 2013, 05:15:14 pm »

I go on ebay for small quanitites of o-rings e.g. http://stores.ebay.co.uk/FitPrice/_i.html?_nkw=75mm+o-ring&submit=Search&_sid=799700493

Bear in mind quite a few vendors quote external o-ring diameter, which isn't technically correct. This can catch you out, so check the spec carefully (ask me how I know!).

Sub driver

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Re: Welman build
« Reply #79 on: August 14, 2013, 09:44:35 pm »

Bbdave.
Have you tried your local bearing suppliers, they stock o rings too.
at mine you can order what you want and if not in they get them the next day.
Last time I wtd 4 of different size cost me "
1.00.
regards sub.
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Subculture

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Re: Welman build
« Reply #80 on: August 14, 2013, 09:56:12 pm »

That's assuming you have a local bearing supplier. Used to have one, but they disappeared along with most of the small industry in London.

Sub driver

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Re: Welman build
« Reply #81 on: August 14, 2013, 10:52:18 pm »

Hi.
Seek and ye shall find.....
But comming from a good old northern engineering district certainly helps, we even built some of the x craft...and that company is still very much alive...unlike that german ship.
Up north we have a long engineering standing, still  alive I am glad to say.
Regards to all.
Sub.
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Subculture

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Re: Welman build
« Reply #82 on: August 15, 2013, 03:39:14 pm »

High rents have pushed pretty much all industry out of the capital. Seek all you like, but it's going to be mail order I'm afraid.

bbdave

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Re: Welman build
« Reply #83 on: August 15, 2013, 07:39:30 pm »

Thanks Davy1 I ordered the rings yesterday afternoon they arrived today :} 




Dave
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bbdave

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Re: Welman build
« Reply #84 on: August 29, 2013, 05:29:23 pm »

I have just been testing my pump and a 500ml I.v. Bag it will fill to 500ml in 24 seconds I got just under 700ml in but will keep the max to 600 ml if needed the bag is still mailable at that.


 It does need to lie flat in the WTC other wise it fills unevenly causing high pressure spots and risk of the bag bursting sending 500ml of water across the kitchen  %) {:-{ .


Dave
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Subculture

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Re: Welman build
« Reply #85 on: August 29, 2013, 06:44:40 pm »

That's a good pumping speed for a peristaltic, more than a match for a geared pump in fact. Some put the bag in a small vented cylinder of it's own, which helps constrain the proportions, and prevents it moving and/or chafing against other items inside the boat.

bbdave

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Re: Welman build
« Reply #86 on: August 29, 2013, 06:55:22 pm »

I have a geared pump a Kavan pump at least I think it's geared


Dave
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Subculture

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Re: Welman build
« Reply #87 on: August 29, 2013, 09:51:10 pm »

Oh right. Sorry thought you were using the TT neptune pump. Fair enough.

bbdave

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Re: Welman build
« Reply #88 on: August 31, 2013, 03:46:13 pm »

Hi just testing the app. for resizing pictures hopefully this works should be a picture of my test tank  :}
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bbdave

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Re: Welman build
« Reply #89 on: September 04, 2013, 04:10:31 pm »

As that seemed to work here's where i am at the moment I'm waiting for some bits for the wtc to be made and a couple of bits to be delivered. the hull is coming on not to much detail but what there is its big.

Dave
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Subculture

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Re: Welman build
« Reply #90 on: September 06, 2013, 06:19:43 pm »

Looking good. Been busy with the old filler and sand paper. Have you substituted the earlier aluminium rudder, rear hydroplane for brass?

bbdave

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Re: Welman build
« Reply #91 on: September 06, 2013, 08:48:13 pm »

I changed to a brass rudder because it made soldering it all together alot easier the hydroplane is still Ali

Dave
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salmon

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Re: Welman build
« Reply #92 on: September 06, 2013, 08:49:45 pm »

This sub looks great. I like the way it is shaping up!
I asked myself what sub is this, but duh, it is in the title of the build.
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bbdave

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Re: Welman build
« Reply #93 on: September 20, 2013, 03:11:40 pm »

I have my endcap bits now laser cut by a chum at work i'm not sure if i get enough seal though so my need to get the centre disc made slightly bigger if i install the cap and add a little water then blow into the other end as hard as u can i get a few drips out through the seal not sure what pressure i can blow at though.

A quick Google search shows about 2psi is this sufficient for a model sub? max depth would be 1.8m.
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Subculture

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Re: Welman build
« Reply #94 on: September 20, 2013, 04:36:07 pm »

You'll be a bit over 2 psi at 1.8m (0.1 bar or 1.47psi per metre).

Sounds like you've gone a bit too low on your o-ring compression. I see you've gone for radial seal compression, which is a bit more tricky, bearing in mind the differences in internal pipe tolerance, which tend to be fairly sloppy. I turn them to fit each end, if you have to go down the laser cutting route, it's better to measure your pipe carefully, and either go for a higher o-ring compression or use a larger o-ring cross section.

bbdave

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Re: Welman build
« Reply #95 on: September 20, 2013, 08:38:37 pm »

I think I'll get a couple more discs done as it is free just a fraction bigger these ones give about 12% compression so 15%  may prove better. the discs are 4mm so a 3.53 ring has space to squish  into, a 4mm would be unable to compress in a 4mm groove, right?.


Dave
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Sub driver

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Re: Welman build
« Reply #96 on: September 20, 2013, 09:43:05 pm »

Hi.
Just a thought....why dont you put an o ring on the shoulder and go for axial compression on that one as well as what you have.
A friend of mine went your route with radial
Compression  and after a short time they actually cracked the acrylic tube.
As sub culture quiet rightly says getting it just right is tricky, as the tube dimensions leave a lot to be desired if you did you will have a double seal one internally and one external.

Just a thought for the small price of the o rings.

Regards sub.
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Subculture

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Re: Welman build
« Reply #97 on: September 20, 2013, 10:44:27 pm »

A friend of mine went your route with radial compression  and after a short time they actually cracked the acrylic tube.

I agree that acrylic is finicky stuff compared with other plastics, and extruded acrylic tubing is full of stresses unless normalized (not really very practical for the hobbyist) but in all honesty I've never found that it's so fragile it can't take the compression of an o-ring. Perhaps something else may have been wrong with that tube, maybe it got dropped or came into contact with some chemicals that interacted with the plastic.

12% compression is too low for the inside bore of extruded tubing. I would aim for 15%, and go towards 20% if it's really Himalayan like.

Quite correct about the width of the groove, you must allow a good gap for the o-ring to extrude, too much is better than too little.

Circlip

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Re: Welman build
« Reply #98 on: September 21, 2013, 02:12:03 pm »

Just another couple of points.
 
 1. Why are you using Acrylic for the end caps? Any of the thermoplastic or thermosets for that matter would do.
 
 2. Have you consulted one of the Tinternet suppliers of "O" rings technical tables for the correct groove dimensions?
 
 You can use the wet finger "It looks right" technique but the manufacturers charts give guaranteed results.
 
  Regards  Ian.
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Subculture

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Re: Welman build
« Reply #99 on: September 21, 2013, 02:20:00 pm »

Acrylic laser cuts well, unlike most other thermoplastics. however i think the discussion was centred more around acrylic tubing, and that tends to get used because people like transparent cylinders, and also you can get it in a wide range of sizes. Polycarbonate is a better alternative, but costs a good deal more. PVC tubing is available transparent, but tends to be very expensive compared with the opaque plumbing stuff, and offers no other advantage.

Datasheets can be a bit misleading, as they tend to give slightly higher compression percentages than we need for models. 15-20% of the o-ring cross section is more than adequate
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