DIY Pressure Pot

[tursiops]

I've made a pressure pot for my computers out of a waterline filter, per some threads on SB.
I understand the pros/cons of putting water in the chamber versus air, with respect to possible chamber failure.
However, someone said it was bad for my computers to pressurize them with air, that I should definitely submerge them. He did not know where he got that info.
Is this true?

 

[NAM001]

I dont see anything relevant about the statement. psi is psi

 

[tbone1004]

I've made a pressure put for my computers out of a waterline filter, per some threads on SB.
I understand the pros/cons of putting water in the chamber versus air, with respect to possible chamber failure.
However, someone said it was bad for my computers to pressurize them with air, that I should definitely submerge them. He did not know where he got that info.
Is this true?

water is better since it's not compressible so you won't have an explosion... I don't know why pressurizing in air would be an issue though.

Helium is a problem since it can get past the seals which is why normal dive watches can be small, but the ones designed for saturation diving are like 4x the size. Nothing to do with the pressure, everything to do with the helium.
I suppose it is possible that air could get past the seals and if that happens and you bring it up too fast it wouldn't offgas, but I'm not familiar with that happening. Either way, I would fill it with water in case something fails so you just get a wet floor and pants vs. shrapnel flying everywhere.

 

[Graeme Fraser]

I've asked the attendant if I could keep my DC on during a couple of 5ATA chamber rides. He said it was OK but I would have to leave it in a water filled bucket. Mind you, it was probably more to manage the risk of elevated oxygen and potential electrical discharge than concern for my computer.

 

[tursiops]

I've asked the attendant if I could keep my DC on during a couple of 5ATA chamber rides. He said it was OK but I would have to leave it in a water filled bucket. Mind you, it was probably more to manage the risk of elevated oxygen and potential electrical discharge than concern for my computer.

Interesting!

 

[The Chairman]

Any gas molecule is smaller than any liquid molecule. They can slip past seals designed to keep liquid out. I don't know that this will hurt them, but I know it can. Mind you, we're not talking huge pressures here, so if it were my PDC, I wouldn't have an issue with that. However, should the pressure vessel fail, water is far safer.

 

[Akimbo]

Helium is a problem since it can get past the seals which is why normal dive watches can be small, but the ones designed for saturation diving are like 4x the size.

Small clarification:
Watches designed for saturation diving in Helium Oxygen environments have pressure relief valves. That is because all known transparent materials have high Helium leak rates -- literally through the solid material.

It is impractical to design watch housings to withstand internal pressure in addition to normal external pressure. Many watches designed for sat diving have external depth ratings of 1,000 meters (3,281') or more which explains why they are so stout.

For readers who are not familiar with saturation diving:
Sat divers live in chambers pressurized to working depths that are commonly between 50 and ~300M (165'-~1,000’) for a month or more. That is enough time for Helium to leak into the watch housing and virtually equalize to the dive depth. Saturation decompression is very slow, but too fast for Helium to leak back out of well-made watch housings. Remember, they are not designed for internal pressure at all. That has caused the watch crystal to blow out.

Think I'm kidding?
I had the opportunity to meet the poor bastard that discovered this phenomenon -- up close and personal. I noticed this unusual circular scar inside his left thigh and just had to ask.

He was sitting on a bench in a chamber at the old US Navy Experimental Diving Unit decompressing from an early sat dive. His fingers were laced and forearms resting on his knees because the chambers were small so they had to conform to the cylindrical hull. Suddenly there was an explosion and his thigh was bleeding "like a stuck pig". The corpsman (Navy medic) dug the pieces of the crystal out and treated the wound.

They were wearing Rolex Submariner watches which were the best dive watch made in the 1960s. One of NEDU's PhDs did some research and found the obscure materials data with Helium leak rates. They phoned Rolex and explained the problem. Rolex engineers came up with the tiny Helium relief valve, their patent lawyers went to work, and the Sea Dweller was born. I met him in 1970.

 

[Akimbo]

Any gas molecule is smaller than any liquid molecule. They can slip past seals designed to keep liquid out. I don't know that this will hurt them, but I know it can.

Non waterproof mechanical time and stop watch movements work fine in pressurized Helium environments. Quartz and digital movements... not so much. It's not unusual for sat divers to wear the cheapest wristwatch they can buy in the chamber. They certainly don’t need one during lockouts.

Very well designed stainless steel housings with O-ring seals are virtually Helium tight (defined by no perceptible internal pressure build up for many months). The problem comes when you install a transparent port.

Old CCTV cameras in well made stainless steel housings that successfully made dives on bathyscaphs to over 6,100M/20,000' would fail because Helium would leak into the housing through the transparrent port and then leak into the vacuum tube video sensor. It was very difficult for technicians to unscrew the end bell (plug) due to the internal pressure. It scared the heck out of them when the O-ring blew out and the vacuum tube exploded. Thankfully, this was also discovered before I got into the game.