Sunday, July 26, 2015

Even More Porteau Cove 26/07/2015

With the constant E Coli warnings in the Whytecliff area, Poreau was the next best area. Heather and I had a good two dives. Evan Soukas and Josh Gardner also showed up. It was Evan's first cold water dive after coming back from the Red Sea. There was a ton of divers out, the parking lot was full, and there were several groups out at any one time. Very busy!

On our first dive, we followed the firehose and had a good time looking around the jungle gym. Heather found an octopus in a small crack. There were huge schools of perch, and the usual giant ling cod. On the swim out, we came across a very unique fish, Ptilichthys goodei, or the Quillfish. This image is not mine, but came from here. The folks at Sea to Sky Scuba helped us identify it. It was very snake-like, and the one we found was orangey yellow, and about a foot long. Very cool!

I got some video. The first clip is the octopus in the crack, and the rest is of the schools of perch.

On our surface interval, we had some small bird visitors. Two small brown birds were very used to people, and almost ate food out of our hands. They were very cute. The granola bar we shared with them was a bit sticky, and the poor birds had a bit of a hard time with it!

Heather got a bit of video too.

On the second dive, we decided to go under the dock. Unfortunately the visibility there was not that good. Most of the dive was brown rock. But we did see some big schools of perch, as well as a very large moon jellyfish. Also, we found a Cresi mask, and reunited it with its owner in the parking lot. Good karma!

More Porteau Cove 25/07/2015

I hadn't been out for a scooter dive in a long time, so when Vlad asked me, I was in!

We headed out to Porteau Cove to do a long planned bottom time with some decompression on oxygen. Our total dive time was about 110 minutes. For the dive, we spent most of our time going north along the wall past the Nakaya. The visibility was quite good. Scootering out along the wall show-cased just how interesting the large jagged rocks were. They weren't covered in a lot of life, but that was part of why they were cool. Interspersed in the cracks were small cloud sponges, and many many rockfish. We even came across a lone vermillion rockfish, something you didn't see often.

There were a bunch of old railroad rails, large logs, and a big lion's mane. There were tons of giant white nudibranchs, along with their ribbon egg masses.

On the way back, we stopped past the Nakaya, but the visibility there was awful. Our decompression was done after scootering past the Grant Hall and the fire hose. We amused ourselves by watching the collection of flatfish.

I was getting more used to my new glove system, but on this dive my left glove flooded. I found the problem after. The inner ring that held the glove in place had come loose. So, I would add checking that to my list of pre-dive things.

Porteau Cove 06/07/2015

Heather and I went out to Porteau Cove for a fun dive. It was indeed!

We went along the firehose and got some good pictures. Giant plumose anemones.

Armored sea cucumber.

A rockfish with a diver light in the background.

And Daryl found a pair of shades. Nothing better than treasure!

Wednesday, July 8, 2015

Temperature and its Effects on Cylinders

With the heat wave lately, I started thinking about the cylinders in the back of my truck. Could the heat cause them to fail? How much heat would actually be needed? I decided to find out!

(Without reading further, the summary answer is more than you would ever get on the hottest summer day. To get close, you'd need to heat your cylinder to 150 degrees C).

I apologize for this all being in Imperial. I was lazy and didn’t find easy Metric examples J If I made any horrible mistakes, please let me know. I included the original online source material at the end, and extend full credit to them for this information. Vlad also helped by checking my work, and I included his suggestions. Thanks Vlad!

All these calculations assume a known good cylinder, in VIP and hydro, with good burst disks. If you have an unknown cylinder, it may be wise to be more conservative.

Now, on to the math!

Charles Law states (Pressure x Volume)/Temperature is constant, meaning that pressure rises with temperature to keep their ratio a constant if the volume remains the same. As a formula, that means:

P1/T1 = P2/T2

Rearranging that, we can solve for the end-pressure:


P1 is the initial fill pressure; let’s say 3500psi for high pressure steel cylinders.
T1 will be the temperature at which the fill was done. Let's assume a moderate indoor temperature, say 24 Celcius, or 75 Farenheit, or 535 Rankine. Charles Law uses Rankine, so don’t forget that part!
T2 will be the worst-case temperature in your car/trunk, lets' say 60 Celsius, or 140 Fahrenheit (almost no way in our climate) or 600 Rankine. So let’s do the math!

P2 = 3500(600/535)
P2 = 3925psi

Burst disks are designed to fail at 5000PSI for aluminum, and 5250 for high pressure steel (US source). So even if your cylinder got up to 60 Celsius, you are still far away from that (less than 4000psi).

So what temperature would you need for a burst disk to fail? Let's find out!

5000psi = 3500psi(T2/535)
T2 = 304F or 151C

There is no way your car will get to 151C, unless it's on fire. Vlad pointed out some interesting facts about how hot your can can get which might surprise you. But even those numbers are not close to 151 degrees.

An approximate rule of thumb: for every 1F temp rise (or drop) inside a closed container filled with air, you can expect an approximate 5PSI pressure increase. This is handy to impress your friends when you can predict how much your fill will be reduced when you hit the water!

As with gas-planning, there is no need to guess. Some simple math arms you with facts based on physical laws! You can’t argue with science J

P.S. something else I learned - We all know to store your tank with very low pressure (100 PSI) to keep water out and material stress low. But if that isn't practical, always store it full. In a house fire, the burst disk may blow from heat combined with pressure if the storage pressure is high. If the tank is half full, the tank will likely give way before the burst disk because the material could be severely weakened by extreme heat, and the pressure rise might never reach the rated burst temperature before catastrophic failure of the tank. This is even more important for Aluminum tanks, they will fail sooner than a steel tank in a fire.