I occasionally see questions about manifolds for triple or quad cylinders. It occurred to me that it would not be all that difficult to modify a standard modern doubles manifold.
The simplest option is to remove the isolation valve assembly from the cross-bar and take the valve bonnet to a machine shop. Have them machine/enlarge the top end for a 3/8" straight thread port like on a first stage. You can then adapt to rigid stainless steel tubing.
If that does not meet your geometry requirements, then you can have the isolation or connecting bar cut in two and have both ends machined for either an male pipe thread or a female 3/8" straight thread port, depending on how much material is available — you can keep or eliminate the isolation valve. You might be able to buy the left & right manifold valves with plugs and machine out the plugs, but I'm not sure there is enough material. Keep in mind that this method allows a lot more freedom to configure cylinders. They don’t have to be inline, one or more can be at a different height or even have hubs at a different ends.
Another option that would require less machining but are harder to find would be an old singles valve with a 3/8" straight thread port for a SPG. Remember the port would have to be drilled out to get enough flow, but could be done on a garage drill press. The downside here is no DIN option and harder to find repair parts.
As far as the additional cylinders, it depends on if you want isolation valves or not. No valves are easy. Just take an old leaking singles valve and cut off the valve and burst plug to make a bushing and have a female 3/8" straight thread or ¼" NPT port machined in. You could adapt a DIN fitting to tubing if you want the isolation valve.
My preference for tube fittings is CPV Mark VIII O-Seals, but any HP fitting is fine. You can use any combination of tubing and fittings to make your design work.
Here are some links that may be useful.
http://www.xsscuba.com/graphics/valves/manifold_thermo_new.jpg
XS Scuba Valves
OMS SCUBA Valves & Manifolds http://www.OMSdive.com
Steel and Stainless Steel Flat Faced Tube Fittings (Mark VIII O-Seal)
Attached photos show an old SPG port valve and the AGA Divator 324 that uses stainless steel tubing to connect a second cylinder. There are plenty of other ways to get the job done that will also work; hopefully this serves as food for though.
Edit: It is a good idea to hydro the manifold assembly after fabrication. A lot of hydraulic hose shops can do that for you, but be sure to clean the assembly afterwards. You may also get some grief from dive shops regarding fills, so bring the hydro certificate with you. Considering it is less of a kluge than most dive shop fill stations, many of which were never had manifolds and tubing hydroed, it should not be too much of a problem.
The simplest option is to remove the isolation valve assembly from the cross-bar and take the valve bonnet to a machine shop. Have them machine/enlarge the top end for a 3/8" straight thread port like on a first stage. You can then adapt to rigid stainless steel tubing.
If that does not meet your geometry requirements, then you can have the isolation or connecting bar cut in two and have both ends machined for either an male pipe thread or a female 3/8" straight thread port, depending on how much material is available — you can keep or eliminate the isolation valve. You might be able to buy the left & right manifold valves with plugs and machine out the plugs, but I'm not sure there is enough material. Keep in mind that this method allows a lot more freedom to configure cylinders. They don’t have to be inline, one or more can be at a different height or even have hubs at a different ends.
Another option that would require less machining but are harder to find would be an old singles valve with a 3/8" straight thread port for a SPG. Remember the port would have to be drilled out to get enough flow, but could be done on a garage drill press. The downside here is no DIN option and harder to find repair parts.
As far as the additional cylinders, it depends on if you want isolation valves or not. No valves are easy. Just take an old leaking singles valve and cut off the valve and burst plug to make a bushing and have a female 3/8" straight thread or ¼" NPT port machined in. You could adapt a DIN fitting to tubing if you want the isolation valve.
My preference for tube fittings is CPV Mark VIII O-Seals, but any HP fitting is fine. You can use any combination of tubing and fittings to make your design work.
Here are some links that may be useful.
http://www.xsscuba.com/graphics/valves/manifold_thermo_new.jpg
XS Scuba Valves
OMS SCUBA Valves & Manifolds http://www.OMSdive.com
Steel and Stainless Steel Flat Faced Tube Fittings (Mark VIII O-Seal)
Attached photos show an old SPG port valve and the AGA Divator 324 that uses stainless steel tubing to connect a second cylinder. There are plenty of other ways to get the job done that will also work; hopefully this serves as food for though.
Edit: It is a good idea to hydro the manifold assembly after fabrication. A lot of hydraulic hose shops can do that for you, but be sure to clean the assembly afterwards. You may also get some grief from dive shops regarding fills, so bring the hydro certificate with you. Considering it is less of a kluge than most dive shop fill stations, many of which were never had manifolds and tubing hydroed, it should not be too much of a problem.
