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Old 04-10-2016, 14:26   #1
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LPG bottle drainage

Hi!

Have a small LPG bottle residing in a laminated bucket. In the bottom of the bucket there is a hole that drains via a hose through the hull, above the waterline. The hole of the bucket is higher than the through-hull.

We had a leak near the LPG bottle and it all leaked out this way, as the gas alarm never sounded (it works, verified).

Leak is fixed, but we want to replace the LPG bottle with a larger version. As storage space is limited, this means the drainage hole in the containing bucket will end up at the same level or slightly lower than the through-hull.

I am thinking that, in case of a leak, if the gas fills up a few centimeters in the bucket, it will pour out through the hole, into the hose, out through the through-hull, due to pressure? I should probably keep the hose as short as possible in this scenario.

If yes, I can begin laminating a new larger bucket for the large LPG bottle.

What's your experience of this, please?
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Old 04-10-2016, 15:03   #2
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Re: LPG bottle drainage

I'm not sure I follow you, but think of it like water, if water would drain, well the the gas would too.


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Old 04-10-2016, 17:58   #3
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Re: LPG bottle drainage

Quote:
Originally Posted by a64pilot View Post
I'm not sure I follow you, but think of it like water, if water would drain, well the the gas would too.


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Propane is heavy than air, if a leak should occur, the pressure of the tank will force it out.
Always check your fittings regularly with soapy water, inside the container, and wherever fittings that are attached to the appliances that you use.


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Old 04-10-2016, 21:33   #4
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Re: LPG bottle drainage

What kind of boat do you have? If you have a sailboat and heel over in the direction away from your throughhull could the propane escape over the top of the bucket?
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Old 05-10-2016, 06:36   #5
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Re: LPG bottle drainage

Quote:
Originally Posted by a64pilot View Post
I'm not sure I follow you, but think of it like water, if water would drain, well the the gas would too.
Exactly. Think of how water would drain.

And if all of the water would not drain, then all of the gas will not drain either. Most importantly of all, it takes only a small amount of propane to create an explosion big enough that you don't want to be around it! If every last bit of the propane cannot drain out, then you have a problem!
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Old 05-10-2016, 06:52   #6
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Re: LPG bottle drainage

Quote:
Originally Posted by denverd0n View Post
Exactly. Think of how water would drain.

And if all of the water would not drain, then all of the gas will not drain either. Most importantly of all, it takes only a small amount of propane to create an explosion big enough that you don't want to be around it! If every last bit of the propane cannot drain out, then you have a problem!
The minimum concentration of a particular combustible gas or vapour necessary to support its combustion in air is defined as the Lower Explosive Limit (LEL) for that gas. Below this level, the mixture is too “lean” to burn. The maximum concentration of a gas or vapour that will burn in air is defined as the Upper Explosive Limit (UEL). Above this level, the mixture is too “rich” to burn.
The range between the LEL and UEL is known as the flammable range for that gas or vapour.
For propane the range is:
LEL 2.1% volume in air
UEL 9.5–10.1% volume in air
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Old 05-10-2016, 07:00   #7
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Re: LPG bottle drainage

Quote:
Originally Posted by GordMay View Post
The minimum concentration of a particular combustible gas or vapour necessary to support its combustion in air is defined as the Lower Explosive Limit (LEL) for that gas. Below this level, the mixture is too “lean” to burn. The maximum concentration of a gas or vapour that will burn in air is defined as the Upper Explosive Limit (UEL). Above this level, the mixture is too “rich” to burn.
The range between the LEL and UEL is known as the flammable range for that gas or vapour.
For propane the range is:
LEL 2.1% volume in air
UEL 9.5–10.1% volume in air
In other words, if enough propane has leaked into the locker but cannot drain, and the air/fuel ratio is adequate, you basically have a bomb on board.

A critical fact is missing from the OP's description, which is exactly how much lower the bottom of the locker will be than the outlet. As to how much lower is too low, that question is above my pay grade.
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Old 05-10-2016, 07:07   #8
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Re: LPG bottle drainage

Quote:
Originally Posted by Suijin View Post
In other words, if enough propane has leaked into the locker but cannot drain, and the air/fuel ratio is adequate, you basically have a bomb on board...
Yes.
A "little" bit of propane is explosive, whereas a "lot" of propane isn't.
Anything between 2.1% and 10.1% is explosive.

LEL 2.1% volume in air
UEL 9.5–10.1% volume in air
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Old 05-10-2016, 07:23   #9
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Re: LPG bottle drainage

Quote:
Originally Posted by GordMay View Post
Yes.
A "little" bit of propane is explosive, whereas a "lot" of propane isn't.
Anything between 2.1% and 10.1% is explosive.

LEL 2.1% volume in air
UEL 9.5–10.1% volume in air
Dang Ford you are really taking me back to a former life with this one. ( was gas free engineer in navy ) haven't even thought about lel/uel in about 25 years.
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Old 05-10-2016, 08:15   #10
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Re: LPG bottle drainage

And what if it leaks out faster than it can drain?

A bucket is no good as a gas locker. There should be no communication between the gas locker and the boat's interior.

This is not something to screw around with. Accidents are fairly rare, but spectacularly destructive when they occur. Read up on "fuel air bombs".

ABYC standards are here:

https://law.resource.org/pub/us/cfr/....A-01.1993.pdf


LPG cylinders, cylinder valves, safety devices and regulating equipment shall be secured for sea conditions and readily accessible, and shall be located:

1.12.1 on the exterior of the boat where escaping gases
will flow directly overboard, the cylinder valve, regulators,
and safety devices shall be in a ventilated location
protected from the weather and against mechanical
damage, or

1.12.2 in a dedicated locker which shall be:

1.12.2.1 vapor tight to the hull interior,

1,12.22 located above the waterline,

1.12,2.3 constructed of or lined with corrosion resistant
materials,

L12.2A equipped with gasketed cover which:

1 12.2.4.1 opens directly to the atmosphere outside the
boat,

L12.2.4.2 opens only from the top,

1.12.2.4.3 latches tightly,

L12.2.4.4 is capable of being quickly and conveniently
opened without tools for operating the cylinder valves,
testing the system for leakage and viewing the pressure
gauge.

1.12.2 .. S vented at the bottom by a dedicated vent,
Ll2.2S 1 led outboard without pockets through the huH
sides to a point lower than the locker bottom but above the
waterline,

1.12.2.S.2 located at least two feet distant from any huH
opening to the boat interior, and

L12.2.S.3 located at least two feet distant from an
engine exhaust terminus which is below the level of a vent
outlet.

1.12.2S4 with a minimum diameter of any component
in the vent system not less than 12.5mm (1/2 inch) inside
diameter.

1.123 When means of access to the locker or housing is
open, the cylinder valves shall be capable of being
conveniently and quickly operated and the system pressure
gauge dials shall be fully visible.

1.12A Storage provisions for unconnected reserve
cylinders, filled or empty, shall be the same as for the
cylinder in use.

1.12.S Lockers shall not be used for storage of any other
equipment.
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Old 05-10-2016, 08:16   #11
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Re: LPG bottle drainage

Quote:
Originally Posted by denverd0n View Post
Exactly. Think of how water would drain.

And if all of the water would not drain, then all of the gas will not drain either. Most importantly of all, it takes only a small amount of propane to create an explosion big enough that you don't want to be around it! If every last bit of the propane cannot drain out, then you have a problem!
Like water, propane can overflow.
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Old 05-10-2016, 09:25   #12
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Re: LPG bottle drainage

I suggest buying (or possibly building) an ABYC compliant propane locker. Your current system is far from compliant but if you're going to do something, I suggest doing it right.


So, it appears your plan is no good.
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Old 05-10-2016, 09:47   #13
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Re: LPG bottle drainage

OP posted -
"drainage hole in the containing bucket will end up at the same level or slightly lower than the through-hull"

Dockhead posted ABYC - "outboard without pockets"

If you have a low spot in the drain, water will get in it. Once propane is out of the pressurized bottle it is gas, not liquid. Not gonna drain.
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Old 05-10-2016, 10:48   #14
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Re: LPG bottle drainage

Quote:
Originally Posted by cal40john View Post
OP posted -
"drainage hole in the containing bucket will end up at the same level or slightly lower than the through-hull"

Dockhead posted ABYC - "outboard without pockets"

If you have a low spot in the drain, water will get in it. Once propane is out of the pressurized bottle it is gas, not liquid. Not gonna drain.
Oops, I missed that one.

Yikes, that's even worse -- MUCH worse.

As Cal40John said -- a little water in there, and no more gas draining at all.

This is a disaster waiting to happen.

Don't mess around with propane, which is a violent explosive when mixed with air over a quite range of mixture strengths. It has more explosive power per unit of weight than TNT.

Do it right, which means following ABYC, or convert to electric.

If an ABYC compliant locker is too expensive or too much trouble -- the only reasonable "poor man's" solution to this problem is to hang the bottle on the outside of the pushpit where leaks will not find their way into the interior of the boat. Which I think can be made ABYC compliant, too.

Here's some good reading on the subject:

http://www.practical-sailor.com/issu...s_11344-1.html

With lots of helpful tips. Note also the "Surveyor's Report", with details on a propane explosion on a boat with a home-made non-compliant gas locker, which killed the owner in a grisly manner.
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Old 05-10-2016, 12:28   #15
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Re: LPG bottle drainage

Just want to "ditto" what Dockhead said. This is NOT something that you want to do wrong! You absolutely CAN blow up your boat with propane, if you don't do it right.

A lot of people think that propane is just too dangerous to have on a boat. It is not. It can be a very safe, efficient, and cost effective fuel. But you MUST be aware of proper installation and use standards, and FOLLOW THEM!
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