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Old 17-11-2015, 17:37   #1
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CNG Supply Line - Tank to Stove 20'

Hi from a new member here!

I recently purchased a 1984 Catalina 38 with a CNG stove and tank. During the pre-purchase survey it was discovered that the supply line to the tank had a major leak. While tracing the line back to the cng stove, I discovered that a screw had punctured the line mid way during a previous installation of a water heater. Long story short - the cng supply line has to be replaced since it is inadvisable to cut it and use a coupling below deck.

After many, many calls and emails I have been unable to locate a distributor or source of supply here in CT who can provide me with 20' of approved CNG hose with appropriate end connections. Defender and West Marine do not even reply when asked. I even got involved with Parflex and two of their distributors. What is the great mystery to finding a supplier who can make up a connection hose for my tank and stove? What would seem to be straight forward and reasonably simple to resolve is turning out to be nearly impossible. Thx! bill
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Old 17-11-2015, 17:51   #2
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Re: CNG Supply Line - Tank to Stove 20'

Sounds like you're looking too hard for a "marine" solution. I had my hose made by a local outdoor grilling store.
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Old 17-11-2015, 18:09   #3
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Re: CNG Supply Line - Tank to Stove 20'

You don't tell us where you are. Have you investigated how easy it is to get CNG tanks refilled where you will be sailing?
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Old 17-11-2015, 18:22   #4
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Re: CNG Supply Line - Tank to Stove 20'

First CNG is lots safer then propane as NG is lighter then air and is far less a problem on boats. Generally any hose listed for propane will meet CNG specs too. Though you might need a 1/2" hose instead of 3/8" hose. Ebay will be your friend for that Propane Natural Gas Heavy Duty Flex Hose 25 ft with 1 2 Pipe Fittings | eBay
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Old 17-11-2015, 18:28   #5
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Re: CNG Supply Line - Tank to Stove 20'

Convert it over. CNG too hard to find and tanks to hard to carry as I remember. Maybe you have some kind of small tank?
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Old 17-11-2015, 18:39   #6
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Re: CNG Supply Line - Tank to Stove 20'

http://www.homedepot.com/p/Unbranded...0725/203073943
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Old 17-11-2015, 19:26   #7
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Re: CNG Supply Line - Tank to Stove 20'

Like he said, but in 1/2". The line and fittings are "CSST" or Corrugated Stainless Steel Tubing system. Very common in natural gas installations in residential construction.

Look this over:http://static1.1.sqspcdn.com/static/...Cu3yJRF8aug%3D
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Old 17-11-2015, 19:43   #8
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Re: CNG Supply Line - Tank to Stove 20'

Is it very different from propane lines? Westmarine carries a number of lengths, forget the brand, comes with standard fittings.


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Old 17-11-2015, 22:43   #9
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Re: CNG Supply Line - Tank to Stove 20'

Quote:
Originally Posted by Dennis.G View Post
Like he said, but in 1/2". The line and fittings are "CSST" or Corrugated Stainless Steel Tubing system. Very common in natural gas installations in residential construction.

Look this over:http://static1.1.sqspcdn.com/static/...Cu3yJRF8aug%3D
While CSST tubing meets all US plumbing codes, I have some concerns of its suitability on boats. The tubing is very thinwall tubing with a maximum working pressure of only 5 psig. The fittings are brass.

The issues with it are several.

First you have cheap brass fittings with a high zinc content in contact with the stainless steel tubing. There are galvanic issues between the tubing, fittings and sealing ring in a salt air environment. The manufacture recommends sealing the ends with silicone tape if exposed to weather. Myself I don't think that would be adequate in a salt air environment.

Second the pressure rating is only 5 psig and the material is designed to be installed in buildings that generally do not heel over much. I am concerned that with the boat working in a seaway that over time, the thin tubing may wear as it passes through bulkheads, etc.

That, and with a really low working pressure, to me makes it less then desirable to use on boats. Most hose for propane or CNG will have a 200 to 325 psig working pressure. Mainly as propane pressures can exceed 150 psig in a hot tank.

CNG is stored at 3000-3600 psig. If the gas pressure regulator failed open (which can happen though rare) the hose needs to be able to contain the pressure of the propane or the CNG second stage regulator. CSST tubing will not do that.

For those reasons, I don't think CSST tubing would be safe on a boat. But that's just me. The hose in my link on the other hand was tested to 750 psig without bursting.
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Old 18-11-2015, 03:46   #10
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Re: CNG Supply Line - Tank to Stove 20'

Greetings and welcome aboard the CF, Bill.
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Old 18-11-2015, 05:53   #11
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Re: CNG Supply Line - Tank to Stove 20'

Wow! You guys are tremendous - nine answers in less than 12 hours! Thank you all. In my original post, I think I used "CT" rather than spelling out Connecticut.

More to confuse you all . . . I neglected to mention that the old gas line was a co-extrusion, that is, two dissimilar materials one extruded over the other. I investigated into this a little and found out that the inner tubing is a carbon-filled, electrically conductive polymer designed to provide continuity between the tank and the stove ( . . . I think!).

Even though my end fittings were brass, Parflex, the largest mfr of specialty hose, said they would not sell me hose specific for CNG without their proprietary SS fittings and then, only through one of their distributors. One distributor quoted me over $350.00 for 20' with SS connections. The other just dropped the ball completely.

Even Force 10, the maker of the stove who approves their product for CNG conversion from propane, has not responded via their retail outlet, Defender right here in CT.

So, this is what got me started in writing to you all on this particular matter. I am very interested in your responses and especially so in sailorchic34's insights. Appreciated, though I don't think CSST in this particular environment would be the best answer. The Parflex hose has abrasion resistant braided Kevlar between the co-extruded components. I would really like to keep the CNG system because of the obvious safety parameters over propane. So, it may be that I will have to buy 20' of hose with two fittings for the ungodly sum of $350+ to resolve this issue.

Thanks again, everyone!
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Old 18-11-2015, 06:12   #12
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Re: CNG Supply Line - Tank to Stove 20'

These guys have every hose and fitting know to man in stock and will get it to you tomorrow if you want:McMaster-Carr

You will just have to decide what you consider "acceptable". Personally I would have no problem with (high quality) brass fittings in this application (your stove almost certainly has brass fittings in it), and also have no problem with hoses with pressure ratings that are code approved.

This is what they specifically list for cng and lpg http://www.mcmaster.com/#natural-gas...e-hose/=zv30c3

But they have all sorts of higher spec hose like -
www.mcmaster.com/#braided-vacuum-hose/=zv33t3

or go depending on the bends in the run - see the LPG and CNG versions of: http://www.mcmaster.com/#standard-copper-tubing/=zv392j
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Old 18-11-2015, 06:29   #13
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Re: CNG Supply Line - Tank to Stove 20'

Would copper tubing not work?
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Old 18-11-2015, 06:52   #14
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Re: CNG Supply Line - Tank to Stove 20'

estarzinger and motion30, thank you for your input. I checked out your McMaster-Carr link and noted that it specifically states "do not use hose with . . . or movable appliances."

The issue here is that the hose is attached to a movable, ie. "gimballed" appliance. My understanding was that metal (any metal) under continuous flexing will work-harden and eventually fatigue (fail). So, I am inclined to stay away from metal hose for that specific reason. If I could find a reinforced, electrically conductive inner lined, co-extruded hose at a fair price, I would buy it! I have also followed sailorchic34's link to ebay which is interesting and, hopefully a suitable choice at a fair price but, so far I have been unable to make contact with the seller to verify that the hose is internally conductive or reinforced. Thx again!
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Old 18-11-2015, 07:08   #15
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Re: CNG Supply Line - Tank to Stove 20'

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Would copper tubing not work?
Until recently, Copper Tubing has not been permitted for use with Natural Gas.

Now, all of the codes currently allowing for the use of copper (type K or L) in natural gas distribution systems contain the restriction that bare copper tube not be used if the gas stream contains an average of more than 0.3 grains of hydrogen sulfide per 100 standard cubic feet of gas (sour gas). Should the gas stream exceed this amount, the codes permit the use of copper tubing if the tube is tin-lined. These requirements are in place to minimize the possibility of sulphation (scaling/flaking) inside the copper tube.
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