How to Use CNG Adapter

[dancrosswis@gmail.com]

Hi Folks,

We had a good Memorial Weekend cruise visiting Door County (WI). Great food with lots of pots going and, a first, a little oven action. And then we ran out of CNG. Water for the last morning's coffee heated slowly on the grill.

Fortunately, Marinette has a CNG pump. I've made a CNG refill adapter along the lines of our Tech Wiki article, modified to include a needle valve as described at http://forums.sailboatowners.com/index.php?threads/cng-refilling.168890/. And, I used it once last year, an episode that left me uncomfortable. So, I thought I'd canvas the experience of others before reconnecting to the hose.

Here is the sequence of events last year (as I recall; I've got contemporaneous notes on the boat), this is at a 3600 PSI pump:

• Tank valve is off
• Attached adapter to tank
• Set needle valve to about 1/4 open
• Attached pump hose to adapter
• Paid the pump
• Turned on the pump
• Adapter gauge pegged at 4,000 PSI (it's limit)
• Pump turned off?
• Opened tank valve
• Tank filled slowly until I shut off the tank value at 2200 PSI. Adjusting needle valve did not appear to affect flow rate.
• No sale registered at the pump

I'm not sure how to interpret what happened. My theory is the pump quickly turned itself off when the pressure at the end of its hose shot up. The CNG that filled my tank may simply have been in the hose?

Next time, I suspect that I should open the tank valve before turning on the pump, so the gas has a larger volume to rush into. How worried should I be about that 4k+ PSI spike?

I haven't found a step by step description of the refill process. I'd like feedback on whether my procedure sounds right. Any suggestions on the needle valve setting? Any other suggestions are welcomed.

Thanks,
Dan Cross
Ennui Went
1968 C34 #159

 

[Benny17441]

That is a lot of pressure to fiddling around with. It is really not worth it to risk your safety and that of others near you for some cooking fuel. I don't think the legalities of the use of homemade or other adapters have been defined, but I would not rule out that if someone caused an accident in one of these stations that charges of negligence and tampering with equipment would be filed and God forbid there would be a fatality. It is just not worth it. For years I operated a propane stove with 1 lb canisters and have also used non-pressurized alcohol stoves so there are economical and viable alternatives out there. I would continue to look for regular portable tank filling stations where you pay and they fill your tank or a trusted tank exchange service but would stay away from the use of adapters.

 

[Stu Jackson]

Benny, that was NOT Dan's question.

I hope Steve Dion shows up, He knows.

 

[Alan Gomes]

Benny, that was NOT Dan's question.

I hope Steve Dion shows up, He knows.

Benny *did* answer one of his questions: "How worried should I be about that 4k+ PSI spike?" I think Benny's answer is well worth heeding.

 

[Richard19068]

Did you read the "directions for using CNG adapter assembly" at the link below? Not exactly on point because the pressures may be different but it implies you should open the tank valve before turning on the pump (which makes sense to me).

A friend of mine does this and says the tank fills to 2000 to 2200 psi (using a 3600 psi pump) in a matter of 15 to 20 seconds and he then turns off the pump. He does not have a needle valve and says you have be ready to monitor the pressure closely when you turn on the pump and be very ready to turn off the pump when the tank gets to 2000 or so. NB, this is not from my first hand experience, just what I have heard from him.

http://www.c34.org/wiki/index.php?title=CNG_Refill_Adapter

 

[Stu Jackson]

Did you read the "directions for using CNG adapter assembly" at the link below?

Thank you Richard, since that link is THE one that Dan used to consider his assembly (he's a C34 skipper and I sent him here hoping Steve Dion would answer him), and that one is the one I link to whenever this subject comes up. Why? 'Cuz there have been many posts about this subject and our C34 website has been the only one, I know of, that has documented the proper way to do it. Please note that the original design was CLEARLY updated with details of the pressure ratings.

Sure, Benny's right, as he always is, but when they started making automobiles they warned about the dangers of refueling them, too. Hell, my ex-wife still hasn't ever pumped her own gas, and she's from Akron. Oh, wait, they only make tires there.

Steve has been using his rig for many years. Works for him, unless he's absent because he blew himself up with it. I haven't heard the BANG yet from here, and I'm close. He continues to, nicely, offer his rig for refills for me.

C'mon, guys, if these things were so unsafe, how the hell do you expect "professional" refillers to do it? Pretty much the same gear, because the gear and the ratings are clearly listed in the link's text. I have never heard of anyone who built one to not show up to work the next day.

 

[dancrosswis@gmail.com]

Thanks for everyone's thoughts. Of course, I want to do this safely. That's the impetus for my post.

The problem I need to solve is this. My boat's across the boarder in the UP (Upper Michigan). The closest tank refill/exchange location I've found is across the boarder in Illinois, about 3.5 hours from the boat. I've exchanged tanks there once, at $100.00.

At the same time that the old CNG refill/exchange locations are drying up, CNG pumps are popping up all around Wisconsin. There's one within a couple miles of my boat. So, the refined problem is, how to get CNG from the pump onboard my boat in a usable form.

Thinking broadly (and with no engineering knowledge), the fill adapter appears to be a simple/direct solution, if it can be done safely. I'm open to other solutions, if there are any. For example, can my 2200 psi tank be replaced with a new 3600 psi tank? Then, how do I step down the pressure to my stove? Can my existing double regulator handle it, or is a new regulator required?

I may have the faith of the uninformed, but all this seems to be a simple problem with an engineering solution.

Again, thanks for all the input.

Dan Cross
Ennui Went
C34 #159

 

[Benny17441]

Stu, there are dangers in any type of refueling but as long as you are conducting it following regulated procedures and using the certified equipment you may be clear of legal consequences but taking on the risk of loosing a limb and then perhaps ending up in jail to save a few bucks is not a fair trade. Not everyone out there possesses the understanding and care to fabricate and properly use a good adapter. Most of us are from a different generation when devising an adapter for any task was applauded but nowadays if it is not an approved product by the corresponding authorities it will surely be blamed for any little thing that happens and no court will deviate from the approved.

 

[Stu Jackson]

Benny, that may be true, but if the equipment is being used at a service station, one would think the station personnel would object to something not safe.

I sent Steve an email asking him to chime in. He's one gentleman I know who uses it, regularly, with success.

 

[Richard19068]

Benny, that may be true, but if the equipment is being used at a service station, one would think the station personnel would object to something not safe.

Stu, In anticipation of doing this I've checked out a couple of CNG stations in my area and there is no attendant around. All automated self service credit card pumps. Kind of unusual.

By the way, I see these adaptors are available on ebay:

http://www.ebay.com/itm/Boat-CNG-Tank-Refill-Adaptor/182161389847?_trksid=p2047675.c100012.m1985&_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=36861&meid=06bf9b7835894aa1a47306212479ae49&pid=100012&rk=1&rkt=10&sd=182080050433

"No Warranty"

 

[Benny17441]

An adapter is a foreign devise introduced into the filling station for the purpose of by-passing the control of the authorized equipment for the dispensing of CNG fuel. The authorized equipment including the tanks are tested, approved and regulated by the authorities. Don't think for one second that if the use of an adapter devise causes an accident with damages or injuries that the user will not be charged with a crime. My point in this issue is that the benefit of a tankful of CNG is not worth the risk or consequences which could arise.

 

[Stu Jackson]

by-passing the control of the authorized equipment for the dispensing of CNG fuel. The authorized equipment including the tanks are tested, approved and regulated by the authorities.

Benny, this is "Chicken Little" thinking. All of the tanks I use and get from our local chandlery are tested and approved. As I wrote recently on this very subject, the reason the tanks were hard to find for a while was that the refiller was in the process of having all of his tanks re-certified. Within a year the cost went up from $15 to $30+!!!

I agree with you that using a way old, non-currently-certified tank is not a good idea.

Using recently recertified tanks should be just fine.

Besides, the cost to refill is less than $3!!! Compare that to $30!!!

 

[Richard19068]

B

Besides, the cost to refill is less than $3!!! Compare that to $30!!!

Compare to $55 the last time I exchanged tanks in April, up from $35 the prior time about 6 months prior. I'm about ready to pull the trigger on one of the ebay adapters.

 

[All U Get]

There is a blow-off valve that could be set for 2200 and added near your guage. If the pressure exceeds 2200 it opens to vent off anything over that amount. A rapid fill heats the bottle and when it cools you probably have about 2000. I had a picture once of the system, I think Steve Dion sent it to me. I'll have to check. We can still exchange bottles for big bucks, but it's safe.

All U Get

 

[All U Get]

Well I can't send the picture because some extension says I can't. The safety valve wasn't teed into it anyway.

All U Get

 

[Bill Roosa]

You have to understand gas laws and the industry.
working pressure is the one stamped on the tank
filling pressure (accounts for the high temp the tank and gas get to when filling) is about 25% higher than working pressure
Rupture (max allowable) pressure is about 25% over filling pressure and is a NEVER EXCEED pressure.
for a 3200 psi tank the filling pressure is around 3500 psi, and never exceed pressure is around 3900 psi.
I took 2 minutes and found
http://www.afdc.energy.gov/vehicles/natural_gas_filling_tanks.html

 

[Rick D]

I have CNG. Not difficult in SoCal to find for a price. I don't have a motivation to change since two tanks will last me over a month. However, I am spending a few weeks in Catalina and was hooking up my replacement tank but found the valve is defective and will not open without venting large quantities of gas. Oh well, no CNG on the island, and the ferry won't allow it, so it's microwave and BBQ.