Filling Station Adapters For CNG and Safety

[zstine]

I called Bert Jabin's yacht Yard in Annapolis today, they're listed as a dealer for Corp Bro's, and was told that they haven't had CNG for about 6mo. He said that people are buying the adapters and filling bottles themselves. So I looked into the fill station adapters and for $130ish in parts you can make one pretty easy, but something else came up in the search. Our marine tanks are, I've read, rated for a 2000psi working load and the filling stations are designed for 3000psi or 3600psi pressures. While I have seen some adapters with pressure gauges, many do not and none have regulators. I've seen video and the tanks fill so quick, self-regulation seems difficult/impossible.
- Have people been filling their tanks to 3000psi?
- Do the fill stations ever turn people away because the marine bottles don't meet the vehicular tank standards?
- Has there been reported issues with tanks or DIY adapters failing at filling stations due to over pressurization?
- What's the group consensus on filling your own CNG tanks at fill stations?

I found an exchange and hour from my home, but they want $109/bottle for $1 in CNG.

[zstine]

I just want to add that one of the first hits and most promulgated adapter designs is very DANGEROUS.

!!NEVER DRILL OUT AND TAP A HIGH PRESSURE FITTING!!

The top hit when searching for CNG adapters is one on a C34.org web page that instructs the maker to Dril and Tap the Tee! seriously!?. This will obviously reduce wall thickness and weaken the fitting. Don't do it! You risk your life when filling 3000psi CNG. Stick to unmodified fittings properly rated for the high pressure. I'm amazed in the long discussions I've read that this issue has not been brought up.

[ExperienceSail]

Where did you find an exchange? I need one!

[zstine]

I'm not sure where you are. Lockwood boat works exchanges the steel bottles. There are several places in CT. But I ended up shipping my AL big tank to Corp Bro's in RI and they ship a full one back. It was about $50 to ship mine and $71 for the exchange and return shipping... about 2 weeks time

[svlamorocha]

Originally Posted by zstine

Our marine tanks are, I've read, rated for a 2000psi working load and the filling stations are designed for 3000psi or 3600psi pressures. While I have seen some adapters with pressure gauges, many do not and none have regulators. I've seen video and the tanks fill so quick, self-regulation seems difficult/impossible.
- Have people been filling their tanks to 3000psi?
- Do the fill stations ever turn people away because the marine bottles don't meet the vehicular tank standards?
- Has there been reported issues with tanks or DIY adapters failing at filling stations due to over pressurization?
- What's the group consensus on filling your own CNG tanks at fill stations?

I spent 3 years building 3000-psi CNG transportation systems right out of engineering school.

Argentine taxi drivers have used 3000-psi CNG for many years (20% of cars run on CNG) and there is never an issue because everyone uses the right equipment, except for the odd foreign RV that blows up when someone tries to fill a system rated for 2000 psi using an adapter...

[Island Time O25]

I've had CNG for 8 years. Never seen a tank rated for 2000 - all exhanges were 3000 rated. In fact when I go to the exchange place I make sure the guy tests the tank to be given out for fill level. Have seen variations from 1800 to 2800. Most of the time they're in 2200-2500 range. None were above 2800.

A few times picked them up at RI from Corp. Definitely a deal if you're in the area anyway. Otherwise retailers in New Egland pass the $20 or so shipping charge per cylinder to customers. Was told that before the PC/enviro/gas prie spikes era shipping was $5 or thereabout.

[er9]

will it say somewhere on the tank the psi rating? i go to exchange every three months and its $45 a tank and two hour drive. would love to be able to fill up at station but no way im trying it on a 2000 psi tank.

[Jim Cate]

sounds like a lot of telling arguments for switching to propane!

Swap possible blowing up your boat to blowing up your CNG tank whilst filling it.

Neither of these outcomes are inevitable, as demonstrated by the number of successful users of each system. For me, the expense and inconvenience of CNG filling are hard to ignore when compared to the ease and frugality of LPG fills. (I have owned and used both).

Jim

[hellosailor]

er9-
In the US, pressure cylinders are generally regulated by the US DOT. And they generally require the pressure rating to be stamped into the neck of the cylinder, along with a manufacturing code and a hydrostatic test date. Hydrostatic pressure re-testing is also required every xx years depending on the tank type and use, and that's one reason many folks exchange CNG and propane bottles rather than refilling them. If you keep the tank past the hydrostatic test date, you have to send it out for the retesting and pay for that. If you exchange the tank, the fill company deals with that.

If CNG standards changed and your tank is obsolete, it is possible that you can't safely refill it, and if someone will take it in an exchange, that's an easy solution. If a filling station "looks the other way" and allows an overfill or fills an expired tank...That's not very bright, considered these things can go BOOM in a very loud way.