Gas Locker non return valve

[Graham_Wright]

Here's a small problem which has emerged during the present Jester Atlantic Challenge and which others, including myself, may well have.

It seems that the gas locker in a stern quarter of one of the boats has a normal but simple drain hole through the hull, and that sailing for days in boisterous conditions has meant that hole has been submerged much of the time, and seawater gurgles in. Consequently, the inside of the gas locker has had several inches of seawater swilling about in there for much of the time. This has led to accelerated corrosion of the bases of the gas bottles, with consequent concern for their safety and integrity.

I'd like to find an economic solution, and perhaps one already exists, which would permit the draining overboard of any leaked gas and also any water that finds its way in there, but which would prevent the ingress of seawater.

Thinking caps on, please....!

I was advised that N/R valves are acceptable.

 

[pvb]

I was advised that N/R valves are acceptable.

I can't see how they can be, as they generally require some small pressure before they open, and leaking gas won't exert any pressure.

 

[Pye_End]

The locker is supposed to be gas tight apart from the drain at the bottom.

Has this changed? - minimum requirement 5 years ago was LPG tight up to the top of the regulator - an open box being sufficient.

 

[prv]

I can't see how they can be, as they generally require some small pressure before they open, and leaking gas won't exert any pressure.

I was thinking the same. Although, an arrangement with a buoyant ball below an orifice slightly smaller than the ball's diameter might work. Most of the time the passage would be clear, but if a wave came rushing up the pipe it would slam the ball across the hole ahead of it. I'm suggesting this in-line in the pipe, not in the locker or outside the hull. I don't know of a specific valve that meets this description but I guess they exist. This only works for a drain that's high enough to basically operate by gravity, but occasionally has a wave shoot up it.

Pete

 

[prv]

Has this changed? - minimum requirement 5 years ago was LPG tight up to the top of the regulator - an open box being sufficient.

Whose minimum requirement? There's no actual law on the matter for private seagoing boats.

Pete

 

[Pye_End]

Whose minimum requirement? There's no actual law on the matter for private seagoing boats.

Pete

BSS. Presumably new builds have to conform (perhaps also all inland vessels). My insurance surveyor also wanted changes in gas to conform, and so also did the insurance company. Didn't have to, but to not do may have left me uninsured for claims caused by be not altering the arrangements. This may not be the same position as all the other older boats out there, but Tranona brought the regs up not me!

 

[Avocet]

Avocet's arrangement might be of interest to the OP. It's a box in the lazarette with a drain tube through the transom and it does, indeed, get the occasional bit of water in it. As the box has no opening sides (only the lid) it's messy to screw the regulator on to the bottle, so I made a simple turntable in the bottom of the locker (just a circle of fibreglass with a bolt through the middle to spin round). The bolt goes into a hole in a nylon block, which is glued to the bottom of the locker. Round the perimeter of the fibreglass circle are three bolts to locate the bottle, with bits of plastic tube over them to prevent electrolytic contact between the bolts and the gas bottle. The attach the regulator, the regulator stays still and the bottle is rotated. It has the added advantage of raising the bottom of the bottle an inch or so above the bottom of the locker (which is nearly always wet).

 

[RAI]

A rubber flap valve over the transom exit might block most of the water and still let gas pass.

 

[prv]

BSS. Presumably new builds have to conform (perhaps also all inland vessels).

The Boat Safety Scheme is an inland-waterways thing - so yes, most inland boats need to conform as a condition of their license to use the waterway. It doesn't apply to seagoing boats, though it's often (and quite reasonably) used as a model for good practice.

There may be something in the RCD for new-build seagoing boats. Plus, of course, there's always the general principle of liability for selling something of unnecessarily dangerous design.

Pete

 

[Graham_Wright]

I can't see how they can be, as they generally require some small pressure before they open, and leaking gas won't exert any pressure.

The suggestion was a flap valve (easier to imagine on the outside of the hull but not exactly practical!). I would think a gravity operated swinging flap would probably be sufficient. Small leakage is unimportant. If the (eventual) outlet is blocked by water, gas will not escape anyway. On a long fetch, leaking gas would accumulate back up the discharge pipe and defeat the object. Perhaps two hull connections would work. One high up would be lower on the problem tack and the heel would create a downwards path. The other low down would sort out the other tack.