Sunday, February 17, 2008

Tec Skills Demonstration

Here's a chap doing an excellent job of demonstrating the skills practiced in the Discover Tech Specialty.

Friday, February 8, 2008

Choosing Tanks for Tech Diving

A student recently asked:

"Ken: I'm planning to take the Deep Class. I have a couple of questions regarding the gear configuration for the class. What size of tank do you recommend? I'm planing to buy a steal tank (and later buy other to make a twin set) and was wondering what size should I buy? It's recommended for tech diving the type of valves that are both Yoke and DIN, the so called Thermo Pro Valves?"

Excellent questions.
Now for the gear questions. Starting with tanks you will probably hear as many opinions as there are divers. I will offer mine and let you know why I feel that way. First, if you are considering tanks that will eventually end up in twins, and diving in deeper than recreational limits with the proper training I would recommend you choose low pressure high capacity tanks. The favorite "gold standard" tanks for years are the Faber LP 104s. Here's the reasons. First, with a low pressure tank you can "bump" the pressure to gain a little extra capacity; especially when they are new and have the + rating which allows for 10% gain. So a 104 turns into a 110 really easy. It also means you have 110 cubic feet at only 2700 psi. You may remember from your open water class that as you go deeper the density increases. At deeper depths little problems can become big issues. If you blow a hp hose at 30' it's a hassle, but if you blow a hp hose at 165' you have serious issues. Keeping the pressure down is always a good thing. It's easier on your gear (regs, hoses, o-rings), and easier to blend mixes if you ever decide to dive trimix or even nitrox in the tanks. Another good tank is the OMS (Faber) 98's. You have to look around for them; many stores now carry the medium pressure (3000 psi working pressure PST or Worthington tanks) They're a great tank, but not ideal based on the previous reasons. Faber also made a LP Steel 112 rated at 2400 psi, but it's a monster. And unless you're a really big guy it's a ton to carry on your back. Now some guys will probably have smoke coming out of their ears about now and swear on twining up a set of HP 100s. I don't fall into that camp. I've seen too many pressure failures at 3500 psi, and don't want to risk it if I'm deep and have a choice.
Valves are less of a choice. You will usually get whatever you get on the tank; and quite honestly there isn't that much difference. Plus, when you twin them up you'll get a new manifold anyway. You are correct in that you want to convert everything to DIN. A captured o-ring is the smartest thing for deeper dives. Most of the newer DIN valves have an insert if you want to throw a yoke on it in a pinch. Pony bottle size is your preference. Usually you want at least 19 cu ft in either aluminum or steel. Some guys dive a 30 cu ft tank; but it's a little large in my opinion. Regulator quality for the pony is a resource (money to spend) question. An unbalaced (less expensive) regulator will work fine, but will breath much harder at depth. Which means you will consume more air than if you had a balanced regulator. And one could assume that if you need to jump to your pony bottle in an emergency, less air consumption is better; especially if you have a small pony. One of the drills we do in class is to calculate and breath off a pony bottle at depth to see what kind of time we actually have. Also, it's nice to have a DIN on your pony as well since it will be much more compact that way.
One of the things we spend a lot of time reviewing and discussing in this class is the gear configuration, so if you don't get all the answers you need we cover it in class. We spend a couple of hours on the beach reviewing gear, the dives, standards, objectives and answering questions.

Thanks for the excellent questions,

Ken Pfau
PADI IDC Staff Instructor
DSAT Tec Deep Instructor

Below is a brief list of current tank manufaturers and sizes:

Manufacturer - Material - Cubic Feet - Service Pressure - PSI/Cu. Ft.
Catalina - Alum - 40 - 3000 - 75
OMS - Steel - 46 - 2400 - 52
Luxfer - Alum - 48.4 - 3000 - 62
Catalina - Alum - 53 - 3000 - 57
Catalina - Alum - 60 - 3300 - 55
Luxfer - Alum - 63 - 3000 - 48
Pressed Steel - Steel - 65 - 3500 - 54
OMS - Steel - 66 - 2400 - 36
Catalina - Alum - 67 - 3000- 45
Faber / Scubapro - Steel - 71.4 - 3000 - 42
Faber / Scubapro -Steel - 75.8 - 2640 - 35
Catalina - Alum - 77.4 - 3300 - 43
Catalina - Alum - 77.4 - 3000 - 39
Luxfer - Alum - 77.4 - 3000 - 39
Luxfer - Alum - 78.2 - 3000 - 38
Pressed Steel- Steel - 80 - 3500 - 44
taylor-Wharton- Steel - 80 - 2400 - 30
OMS - Steel - 85 - 2400 - 28
Faber/Scubapro - Steel - 95.1 - 2640 - 28
OMS - Steel - 98 - 2400 - 24
Pressed Steel - Steel - 100.1 - 3500 - 35
Pressed Steel - Steel - 104 - 2400 - 23
OMS - Steel - 112 - 2400 - 21
Pressed Steel - Steel - 120 - 3500- 29
Pressed Steel - Steel - 120 - 2400 - 20
Heiser /Beuachat- Steel -120 - 3190 - 27
OMS - Steel - 125 - 2400 - 19
Heiser /Beuachat - Steel - 140 - 3190 - 23
Heiser /Beuachat - Steel - 190 - 4400 - 23

Thursday, January 17, 2008

Scuba Regulator Service

Regulator Maintenance

One clear finding from several long-term regulator usage studies is the importance routine maintenance can play in keeping your regulator at peak performance. Students that take the PADI Equipment Specialty course quickly see the benefits of following the manufacturers' recommendations for regular servicing. The small investment in maintaining your life-support gear can pay big dividends in performance. The price of the replacement parts kits for most regulators may range from about $20 to $60, but many warranties cover the cost of parts if you service your regulator at the recommended intervals. Labor charges are an additional charge, but usually run about $60 to $70 depending on the regulator.

How much labor is involved? It depends on the regulator design and the condition the regulator is in when it comes into the shop. Here is the procedure commonly used by a shop for annual service.

Annual Service

The shop will usually start with an external check for corrosion, cracks, and missing or misplaced parts. They remove the mouthpiece and see if it needs replacing. Then the first stage is attached to a cylinder valve that is adjusted to 3,000 psig. The intermediate pressure (IP) and the Magnehelic reading of the cracking effort (CE) are recorded (more on that later).

Next the technician will usually review the regulator's service manual and note procedures for disassembling, cleaning, re-assembling, tuning and check for any service bulletins warnings, cautions or notices. The unit is then completely disassembled, making note of corrosion and worn or broken parts. All parts are placed in an ultrasonic cleaner to remove any corrosion (that blue & green gook) rinsed in water and then blown dry. Assembly is performed per the instructions in the service manual, using the manufacturer's service kits. All dynamic (those on moving parts) O-rings are replaced, and nowadays even the static O-rings are usually replaced. The valve seat is also replaced. On both piston and diaphragm regulators the high pressure air is managed by a high-tech composite valve seat against a knife edge. That seat will wear with usage, and is replaced so you don’t get any seepage or leakage. Once assembled the tuning is done in accordance with the manufacturer's specifications. The first stage is tuned at a low pressure (500 psig or 750 psig depending on Mfg) and then at high pressure (3,000 psig). The unit is then may be put on a Set Seat and Poppet fixture to break-in the high pressure (HP) and low pressure (LP) valve seats. After the seats are broke-in, the second stage is checked for leaks (a leaky diaphragm or box will breathe wet). Final tuning is often performed with the regulator immersed in water, and with the inhalation control knob (if applicable) and the Venturi switch set to the manufacturer's recommendation. The second stage is placed in the water in dive position (face down). The unit is adjusted until there are no leaks. After final adjustment, the unit is placed on a flow analyzer to determine if it is performing properly by fine tuning the second stage to a cracking pressure of 1.5” to 2” of water. All tests are conducted at 500 psig and at 3,000 psig. You can test this at home by putting your second stage in water with the mouthpiece up and it should start to crack once the diaphragm is just over an inch submerged.

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