Building a Dual Tank System without going broke.

Home

I love SCUBA diving, so I want to stay down as long as the air supply will allow. I have looked into a number of systems to decrease my air consumption and increase my bottom time. At the end, I need more air, so dual tanks was right for me. Below I have listed the Pro's and Con's the systems I looked at before building the Dual Tank system.
Single 80CF Tank
The single 80 CF tank is a standard tank size for the recreational diver. This tank is found in dive shops around the world as the standard rental tank.
Single 100 CF Tank  
The single 100 CF tank is a tank that provides another 20 cubic foot of Air time. The tank size is bigger and heavier than the 80 CF counterparts.  It is used by some recreational divers. This tank can be found in some dive shops, but due to a high cost ($350) of the tanks it is not the standard rental tank item. if you can find them you will have to pay more.
Dual-Tanks with Header
The Dual-Tank with Header system has a number of value-added features that go beyond doubling the air supply. The header system allows the diver to isolate tank and regulator in the dive. This can be a value in an extended dive.  Dual 80 CF tanks equal 160 CF that can allow the diver to have doubled the dive time. The dual-tank with header is a dedicated configuration. The tanks are permanently connected together with custom values. The tanks are also banded to hold the tanks from moving. This configuration is heavier and more cumbersome to move, fill, load, and handle. The dual-tank with header can weigh in at 75 pounds depending on the tank size. In addition to the cost issue $900 to $1200 USD for each dual setup 2 tanks, header, and tank bands. The diver will need to use a BC to support a dual tank setup. This configuration is not used by most recreational divers. This tank configuration can be found in some dive shops but is not as the standard rental tank item.
Dual 80 or 100 CF Tanks without Header
The Dual-Tank without Header system has some major advantages for the recreational diver that needs extended airtime. The non-header system also allows the diver to isolate tank and regulator in the dive. As the same as the dual-tank with header the Dual 80 CF tanks equals 160 CF that can allow the diver to have doubled the dive time. The dual-tank non-header is not a dedicated configuration. The tanks can be used at any time as a single tank dive. The tanks are not also banded together. I did not find it necessary to buy a special BC, I used my single tank BC. There are no custom values, no added cost beyond the one time setup. This configuration is not heavier nor is it more cumbersome than handling single tanks. The one time setup will cost $300 USD +/- depending on the gear selected for the dual setup. This configuration is not used by most recreational divers, but could be. This tank configuration can be found in all dive shops because it uses standard rental tanks.

Why I chose to go without a Tank Header

  
After great thought and care I see that this is right setup for me.  I am a large person, 6’-9” I use a lot of air. I am just bigger than the 5’-6” guys I SCUBA dive with.  They do not want me to cause them to exit the water when they have 1500 pounds on the gage and I have only 500.  I also can rent tanks anywhere without issue. In the past, I was always looking for 100 CF tanks. Now, I just ask for an extra tank per-dive… I do not have to worry about the availability of the dual tanks or extra-large tanks. I just dive with my buds.

Setting up Dual 80 or 100 CF Tanks without Header

Parts List:

  • 1 pcs. ¼ inch NPT brass ball value $15 each
  • 2 pcs. ¼ inch NPT brass 90 street elbow $3 each
  • 1 pcs. ¼ inch NPT brass couplings $3 each
  • 1 pcs. ¼ inch NPT brass short pipe nipples $3 each
  • 1 pcs. ¼ inch NPT brass 4 inch long pipe nipples $3 each
  • 2 pcs. ¼ inch NPT Male to Standard BCD Connector (AA04) $5 each
  • 3 pcs. Standard BCD inflator hose $35 each
  • 1 pcs. Nylon pipe sealing tape $1
  • 2 pcs. Standard SCUBA regulators first and second stage (Aeris A2 Regulator) $150 each
  • 2 pcs. Scubapro X Tec Single Tank Adapter $133 each set
  • 2 Poly Cutting boards $15
  • 2 pcs. 8 inch long Velcro tie strap $2
  • 2 pcs. 3/8 inch SS bolts washers and packed nuts (so nuts will not back off underwater) $10

Total Bill = $650+/-

Building the Back Plate
This is straight forward woodshop 101 stuff. Here is what I built for my Oceanic Probe HLC BCD. You will have to build for your BCD design. as you can see I do not modify the BCD, at any point I can remove the two tank stripping system and use the single tank strap. (as seen in the image above)

Building the Transfer Value

    

This again is straight forward Plumbing 101. Here is what I built for my Oceanic Probe HLC BCD. You will have to build for your BCD design and hose lengths.

Setting up the Regulators

  

The first stage regulator drops the tank pressure (3500+/- PSI) to 100 to 150 PSI. This depends what brand of regulator you buy. Each brand has its own designed working pressure. For this reason, I buy two of the same make and model regulator units.  I will start by calling the Regulator assembles Octopus units.
An Octopus is made up by a first stage regulator, second stage regulator, high pressure hose with gage and a BCD inflator hose.  You will need to add a second BCD inflator hose to one of the octopus units.
Air Balance Process

This Air balance System connects the tank systems together at the low pressure side.
Diving on Dual Tanks  

Start with the Octopus unit with the second BCD inflator hose. This Octopus unit is please on the tank that is on the same side of the BCD inflator value. One of the BCD inflator hose is attached to the inflator value. The other BCD hose is connected to the short side of the Transfer Value. The high press hose and gage is routed to the right hand side of the diver. The second stage regulator is also routed to the right hand side of the diver.
The second Octopus is placed on the adjacent tank and the BCD hose is routed to the Transfer Value and connected. The Transfer Value with both hoses should be Velcoed to the BDC sholder strap so that the diver can see and operate the ball value. The high pressure hose of the second Octopus is routed to the right hand side of the diver and Velcoed together with the high presser hose from the other Octopus so that the diver can find and read both pressure gages at the same time. The second stage regulator is also routed to the right hand side and secured to be used as a backup regulator if needed.

To start you will feel the weight of having two tanks on your back, 40 or 50 lbs. Do not be a fool ask for help to stand. In a boat move slowly, hold on to handrails and ask others to walk you to the back of the boat. Before you get in the water, do an equipment check. All values on? Check! Air in the BCD? Check! Watch your tank pressure and enjoy the dive!