Converting LP 72's to doubles

[bevansmw]

I recently bought two old PST LP 72's and just realized that they are actually 65cf at the service pressure of 2250psi. They originally had a plus rating but nobody on oahu (hawaii) renews plus ratings on tank hydrostatic tests, I've asked pretty much everyone that does them on the island already.

My problem is that 65cf of air is a bit small for me, I usually use up the air in an AL80 rented tank faster than the dive buddy I normally dive with so if I go with him with the 72's he's probably going to have a lot of air left after the dive.

My thought is to convert them to doubles so I would have about 130cf of air when using them. They both already have good US Divers K-Valves and my tanks have good vip and a current hydro on them.

Is there any current type of isolation manifold that I can use to convert them to doubles without changing the current K-Valves? I saw some on ebay and the like that look like they would work, but curious if anyone knows a manufacturer that still makes one that I could attach to the current K-Valves to connect the two tanks together.

My BCD will allow me to use doubles... looks like I'm either going to buy some more equipment so I can use them as doubles or re-sell them, I only paid $50 each for the tanks. Just trying to save some $ in converting these to doubles since they already have good valves.

 

[herman]

Several things come to mind. First off, if you are a new diver, give it time, your air conumption rated will come up a lot - your buddy should understand this - plus you don't need to be tackeling doubles if that is the case. The increased task loading and drag alone will likely use up most of your increased capacity.

Doubling the tanks is going to be expensive and add it's own set of probelms. Unless you are way different than your buddy, you will introduce the opposite problem, you end up with way more gas than your buddy at the end of the dive but yet not enought to do 2 dives....are you going to buy 2 sets of doubles? You also need to understand 72's are a different diameter than 80's. You will need a set of properly sized bands and a BC that will accomidate them. Older manifolds can be had off Ebay for a reasonable price but modern ones are going to be expensive. Unless your BC is a Ranger, it's unlikely your BC will accomidate doubles. Even if you have a BP/wing, it's unlikely (and something you need to change if you do) that your current bladder is sized properly for doubles. Plus hauling around doubles when you don't need them is a pain. A new BC/wing, manifold and bands are going to cost you as much as a couple of 80's.

Here are my suggestions:
Just use them for a while on simple dives and rent larger tanks when the need arises....or better yet just swap tanks with your buddy, give them the smaller tanks. While you are at it, take a bouyancy course to improve your dive skills. More gas is not the answer to poor skills.

Sell them to someone who wants 72's. I know there are several vintage divers on island who would likely be happy to give them a good home and then buy some 80's. It's going to cost you less in the long run considering all that is needed to twin them.

 

[Gilldiver]

Twin 72's can be real nice in the 60-130' range and have very nice buoyancy. As long as you have ¾” threads you can use just about any manifold but will have to adjust the bands. In many cases you may need to get a set of custom bands, here is my set of 72’s with a vintage, 2 post, non-isolating manifold.

The bands are custom by Victor, “Detroit mudpuppy” here on SB. Find the center space distance for the manifold you get and the diameter of your tanks (should be about 6.9”) and Victor can make up what you need.

Your BC may need to be changed, but maybe not. I have found very few BC’s that can’t be made to fit, but it may mean cutting some new holes in the center section of the BC – this is not in the Bladder or Bladder bag.

 

[spectrum]

bevansmw

As others have said, yes it can be done. As has also been mentioned doubles are probably to what you need at this point. There are times when these capacities escalate out of control between equipping for multiple dives and trying to match capacity. What if you have a dive buddy with a rebreather!

As a new diver you have lots of room for improvement. Make sure you are weighted correctly, dive in good form. Try to find buddies interested in shallower sites. this will give you more bottom time which is a key to improving. As a hardware solution larger singles are probably a better approach but I would not rush into anything. Meanwhile since you own the cylinders you can set them aside for future use or swap off with a dive buddy who can do nicely on 65 CF.

When you don't have a buddy and want to get wet go skin-diving for an hour or two. This will condition your breathing and legs while growing your comfort in the water. This page goes more into the hows and whys. You are fortunate to be someplace when a mere skin-dive can be a magnificent experience.

Pete

 

[bevansmw]

I figured the doubles were probably a bit too much for me right now still being a beginner. My BC is a ranger so it would accomodate them but would require me to buy some more hardware for it as it is setup just for the single tanks now.

I figure I'll just use the LP 72's and see if I can get them overfilled a bit or if my buddy gets 2 80cuft tanks maybe I could work something out so we do our first dive with the AL80's and second with the LP 72's so we get more bottom time.

Thanks for the info, I'm pretty set on keeping them as singles now though as they'll be great for my wife when she gets certified and maybe then I'll get something like an LP95 or 80 depending on what is available locally.

Maybe later if I want to change them to doubles I'll go down that road.

 

[spectrum]

Maybe I could work something out so we do our first dive with the AL80's and second with the LP 72's so we get more bottom time.

I have seen that work in a number of cases. Now you're getting into adaptive thinking.

 

[zider]

I was in the exact same situation as you a year ago and ended up buying a HP100 tank to give me a bit more gas. The other positive is that this steel tank allowed me to drop a few pounds off of my weight belt due to its buoyancy characteristics.

 

[TSandM]

I believe the other half of the answer to your question is that no, you wouldn't be able to use the same valves as part of an isolation manifold. Valves for a manifold have to have not only an opening onto which one places a regulator, but another opening on the side to admit the crossbar of the manifold. You would have to buy new valves (which generally come as part of the manifold purchase).

I agree with everybody else, that doubling the tanks for gas supply would be frustrating, because you basically have the equivalent of a single 130, which is not good for two dives to any significant depth for someone with an average SAC rate. If you are doing a lot of surf entries, doubles are a PITA, as well (sometimes literally). And the final thing is that doubles are a double-edged sword, so to speak; you get redundancy, which is necessary for diving under overheads, real or theoretical, but you also get a lot more failure points. If you don't get the training to use a manifold effectively, you just have a big single tank with a lot more ways to leak.

 

[Jim Lapenta]

One correction Lynn, there are occaisionally on ebay adapters to convert singles to doubles. THey are essentially two yoke assemblies connected by a tube with a regulator outlet in the center. I have seen them and seen them on tanks and they appear to work. You can shut off each tank to isolate the gas supply but it puts the valve handles in an awkward position. One points backwards and one forwards. THese are vintage set ups and may or may not be in the best of shape depending on the owner. I love my double 72's. Total cost for them was 150 for both tanks, 139 for the manifold on ebay new, and 75 or so for the bands on sale from TDL. SO for about the price of a new 120 I have a sweet set of doubles that when filled well (2800-3000) give me a nice amount of gas.

 

[halocline]

If you want to use both tanks with your existing valves you could get bands and use them as independent doubles if you wanted, or you could even use them in a side mount configuration. My 72 doubles have a standard isolation manifold and 7" bands, I got them both from piranha dive gear for about $200, a very reasonable price for good bands and a manifold. If you want to stay semi-vintage, you could use an old single outlet manifold; I have one and I wouldn't mind selling it. It's really designed more for double hose regs, though, and you would need to find specific bands to fit as the old manifolds have a fixed spacing.

Regarding the fill situation, there should be someone around that will give you a 2500 PSI fill to get you up to 72cft. 2700 brings you to AL80 capacity. As far as the hydro goes, there was a PST document with the REE values for their 3AA2250 72s floating around the board. You might be able to find that, print it out, and give it to a hydro guy. Almost certainly the reason you can't get the plus rating is because they don't have the REE number. If they just don't do it period, that's seriously inept but nothing would surprise me anymore with hydro/vis/filling practices in this sport.

Diving with doubles does take some learning, but 72 doubles are IMO pretty manageable. The tanks only weigh 26 lbs each, so it's nothing like lugging around a set of big HP steel doubles. It took me a few dives to get really comfortable with mine, but I have not yet dealt with any significant emergency with them, no air sharing, etc. So, I'm sure I have more to learn, but initially I actually prefer them to most single tanks. It takes a little more effort to maneuver but buoyancy is more stable and I love the trim. I also find it easier to reach the valves, once you figure out which valves to go for in which situations. (hardly rocket science)

There are more theoretical failure points with doubles, but to me this is a little misleading because there is actual redundancy, which means the consequences of single point equipment failure are less serious.