DIY Pressure Pot with P-Port

kiwi_diver · 10th February 2008, 03:49

Well, I've completed my 1st cut of a pot for testing cell linearity, and for pot-diving my Shearwater. It's made from a PVC plumbing T-piece, typically used for waste water piping. It is 110mm diameter with screw caps with O-rings on all three openings. I've tapped a small gauge and a needle valve with inflator connection into the top cap, and a P-Port into the side cap. I had thought I would need to brace the P-Port externally, but it seems to handle 3 ATM no problems, though the caps are domed a little at that pressure. I've done a quick linarity check on my 3 cells fitted to their P-Plug holder but the most fun has been pot-diving my Shearwater Pursuit!. I switched the backlight on and dropped it in about 4" of water in the bottom of the pot. Then I mounted a wireless camera I happen to have laying around on the inside too, looking down at the Pursuits screen. Closed up and pressurised gently to 3 ATM and watched the video image of the Pursuit via a small hand-held monitor. I did a 30 odd metre dive for long enough (about 13 minutes) to incur Deco, and commenced to bleed out the pot. I bleed out a bit much and missed the 6m stop by about a half metre so the Pursuit started flashing "Missed Deco Stop" which is cool, at least I know it's going to work when I get to dive it in earnest!

Here are some pix of the Pot and video output during the pot-dive.
1st is the pot at 3 ATM.
2nd is the monitor showing the Pursuit at 30m
3rd is ascending (a little fast) through 19m
4th is stopped to 5.6m and missed deco.
5th is looking inside the pot, down past the camera to the Pursuit.
Last is the whole shebang dissasembled.

GKAM · 10th February 2008, 04:41

v. cool setup! I am thinking of making something similar, hence my question here.

Have you pressurized the system any higher than 3 bar ? I assume your PVC pipe is rated at 10 bar, so I guess 1/3 of the pressure is OK, but will you experiment with greater pressures?

I am very curious to see how the p-port behaves. Also it would be good to drill and tap at 3/8 to add an OPV from a 1st stage to ensure the pressure does not rise over the limit.

/GKAM

kiwi_diver · 10th February 2008, 05:15

Hi GKAM, thanks for the comments. I just went to 4 bar with nothing in the pot but the caps were looking ugly at that point so I won't go that high again. I suspect the P-Port will not take too much more and 2 to 3 bar is all I need. I think you would need to build your own P-Port with something more like a 360 degree locking ring rather than those two spring steel things they have as standard. Or build an external clamp to hold the P-Plug in the P-Port.

Good luck with your project!

Packhorse · 10th February 2008, 05:38

Nice one Ray.
I use the same PVC for my can light. I have had it to 52meters (5.2 bar) without issue. Of course this is external pressure not internal.

I did find that the edges on the pipe that mate with the O ring in the cap needed cleaning up to get a good seal. Easily done with some 600 grit+ sandpaper on a flat surface.

Gilles · 10th February 2008, 06:48

As you're intending to use this for testing cells, would it not be quite a bit safer to use smaller pipe? All that surface area creating lots of stress on your pot threads, and explosive force.

kiwi_diver · 10th February 2008, 08:42

Quote: (Originally Posted by Gilles)

As you're intending to use this for testing cells, would it not be quite a bit safer to use smaller pipe? All that surface area creating lots of stress on your pot threads, and explosive force.

True, but I wanted it to be big enough to take a wrist computer or depth guages etc to check them for accuracy against a known gauge pressure down to 30m. With the water filling almost a 3rd, that cuts down the effective air volume inside and we are only talking 3 bar (45 psi).

Gilles · 10th February 2008, 12:29

Quote: (Originally Posted by kiwi_diver)

With the water filling almost a 3rd, that cuts down the effective air volume inside and we are only talking 3 bar (45 psi).

That works out to nearly 700 pounds of force on your end-caps, and a lot more on the pot body. Who knows what kind of shrapnel this t-peice can make.

Be careful. The water fill doesn't mitigate anything.

Keep the pressures lower and keep a barrier between it and your self. This could be an accident waiting to happen.

Dutchy · 10th February 2008, 17:37

Quote: (Originally Posted by Gilles)

Be careful. The water fill doesn't mitigate anything.

It depends. When it's reasonably full there won't be an explosion. With the bursting of the wall the water escapes and the pressure is releaved. The water was not compressed (at least not measurable) so it doesn't expand either hence no explosion.

It is exactly this technique that was used to get rid of many of the Nazi bunkers that were left behind after WWII. They were filled with water and then blown up with conventional explosives.

The key word here is mitigate. I still wouldn't like to be near such a bunker when it is blasted.

Gilles · 10th February 2008, 22:53

Quote: (Originally Posted by Dutchy)

It is exactly this technique that was used to get rid of many of the Nazi bunkers that were left behind after WWII. They were filled with water and then blown up with conventional explosives.

The key word here is mitigate. I still wouldn't like to be near such a bunker when it is blasted.

Have a blob for teaching me something I didn't know

.

10th February 2008, 04:41	#2 (permalink)
GKAM digital nomad Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: May 2005 Location: Greece Posts: 254	Re: DIY Pressure Pot with P-Port v. cool setup! I am thinking of making something similar, hence my question here. Have you pressurized the system any higher than 3 bar ? I assume your PVC pipe is rated at 10 bar, so I guess 1/3 of the pressure is OK, but will you experiment with greater pressures? I am very curious to see how the p-port behaves. Also it would be good to drill and tap at 3/8 to add an OPV from a 1st stage to ensure the pressure does not rise over the limit. /GKAM __________________ Stay #
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10th February 2008, 05:15	#3 (permalink)
kiwi_diver Alias - Ray Mansell Current Rebreather/s: Other SCR Other Rebreather/s: Other SCR Join Date: Aug 2007 Location: Auckland, New Zealand Posts: 157	Re: DIY Pressure Pot with P-Port Hi GKAM, thanks for the comments. I just went to 4 bar with nothing in the pot but the caps were looking ugly at that point so I won't go that high again. I suspect the P-Port will not take too much more and 2 to 3 bar is all I need. I think you would need to build your own P-Port with something more like a 360 degree locking ring rather than those two spring steel things they have as standard. Or build an external clamp to hold the P-Plug in the P-Port. Good luck with your project! __________________ Ray. == Latitude 36 South, where the deeper you dive, the warmer it gets! ==
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10th February 2008, 05:38	#4 (permalink)
Packhorse Custom Title Allowed! Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Jan 2008 Location: Auckland New Zealand Posts: 106	Re: DIY Pressure Pot with P-Port Nice one Ray. I use the same PVC for my can light. I have had it to 52meters (5.2 bar) without issue. Of course this is external pressure not internal. I did find that the edges on the pipe that mate with the O ring in the cap needed cleaning up to get a good seal. Easily done with some 600 grit+ sandpaper on a flat surface. __________________ There are no stupid questions, but there are a LOT of inquisitive idiots. Last edited by Packhorse : 10th February 2008 at 05:41.
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10th February 2008, 06:48	#5 (permalink)
Gilles Worship the feminine Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Den Haag (Netherlands) Posts: 762	Re: DIY Pressure Pot with P-Port As you're intending to use this for testing cells, would it not be quite a bit safer to use smaller pipe? All that surface area creating lots of stress on your pot threads, and explosive force. __________________ Gilles http://www.dirrebreather.com
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10th February 2008, 08:42	#6 (permalink)
kiwi_diver Alias - Ray Mansell Current Rebreather/s: Other SCR Other Rebreather/s: Other SCR Join Date: Aug 2007 Location: Auckland, New Zealand Posts: 157	Re: DIY Pressure Pot with P-Port Quote: (Originally Posted by Gilles) As you're intending to use this for testing cells, would it not be quite a bit safer to use smaller pipe? All that surface area creating lots of stress on your pot threads, and explosive force. True, but I wanted it to be big enough to take a wrist computer or depth guages etc to check them for accuracy against a known gauge pressure down to 30m. With the water filling almost a 3rd, that cuts down the effective air volume inside and we are only talking 3 bar (45 psi). __________________ Ray. == Latitude 36 South, where the deeper you dive, the warmer it gets! ==
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10th February 2008, 12:29	#7 (permalink)
Gilles Worship the feminine Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Den Haag (Netherlands) Posts: 762	Re: DIY Pressure Pot with P-Port Quote: (Originally Posted by kiwi_diver) With the water filling almost a 3rd, that cuts down the effective air volume inside and we are only talking 3 bar (45 psi). That works out to nearly 700 pounds of force on your end-caps, and a lot more on the pot body. Who knows what kind of shrapnel this t-peice can make. Be careful. The water fill doesn't mitigate anything. Keep the pressures lower and keep a barrier between it and your self. This could be an accident waiting to happen. __________________ Gilles http://www.dirrebreather.com
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10th February 2008, 17:37	#8 (permalink)
Dutchy Rene Warries Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: Apr 2006 Location: Nieuwegein (The Netherlands) Posts: 844	Re: DIY Pressure Pot with P-Port Quote: (Originally Posted by Gilles) Be careful. The water fill doesn't mitigate anything. It depends. When it's reasonably full there won't be an explosion. With the bursting of the wall the water escapes and the pressure is releaved. The water was not compressed (at least not measurable) so it doesn't expand either hence no explosion. It is exactly this technique that was used to get rid of many of the Nazi bunkers that were left behind after WWII. They were filled with water and then blown up with conventional explosives. The key word here is mitigate. I still wouldn't like to be near such a bunker when it is blasted. __________________ = This post is environmentally friendly. It is composed of 100% recycled electrons only. =
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10th February 2008, 22:53	#9 (permalink)
Gilles Worship the feminine Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Den Haag (Netherlands) Posts: 762	Re: DIY Pressure Pot with P-Port Quote: (Originally Posted by Dutchy) It is exactly this technique that was used to get rid of many of the Nazi bunkers that were left behind after WWII. They were filled with water and then blown up with conventional explosives. The key word here is mitigate. I still wouldn't like to be near such a bunker when it is blasted. Have a blob for teaching me something I didn't know. __________________ Gilles http://www.dirrebreather.com
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