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Changeover valve safe?


Hudds Lad

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Despite having owned our boat for about 18months now, I've not yet had to swap a gas bottle on it.

To this end i had a closer look in the locker the other day (to see the valve its an acrobatic upside-down head through the hatch affair) and noticed it had some sort of changeover valve, not the single tail that I'm used to.

Stupidly i didn't take a pic, as the phone was indoors and i was evicting spiders from the cratch with a dustpan and brush at the time.

The valve had two tails, but only one is connected to the in-use bottle, the other tucked up near the valve out of the way.

Is this safe? It's not going to start sucking air through an unconnected hose when the magic bottle finally runs out is it, or worse?

 

Just to add, we've no intention of ever using it as intended, we like to know when a bottle is gone and have one in reserve. Would be much happier with a single valve, but that's a future thing to sort if this is ok as is.

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If it is a change over valve, then I would expect it to have a plastic knob with a window in it, through which you can see a red triangle pointing to the bottle that is empty. If there is no knob, it is just a T connection, so you can close the empty bottle and open the full one as required. I think there should be NRVs in the pigtails or the T block, but I would not trust them. It won't suck air, but might vent gas.

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Just now, rusty69 said:

Is it an automatic or manual changeover? I.E can you have 2 bottles connected at the same time, but need to manually turn a valve to connect the other bottle.

I have no idea, i've never come across one before, i'm like a caveman that's discovered fire here :)

 

We're back on Thursday to start the trip to Debdale so will take a pic and add to thread, can't find a pic online that looks close enough to what i remember.

Calor Gas Brand Propane 2 Cylinder Auto Changeover Kit With Opso 5 Year  Warranty - Huddersfield Gas

 

This is as close as i can get to what i recall it looking like, the bulbous bit in the middle and then a tap to the gas pipe underneath, but it was definitely red on top and not grey

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We had an 'owners rental' gas check done on one of our static hire caravans recently as the legislation re switch over valves has changed (they MUST  now be fitted with an over pressure device) and I actually asked the gas-man about only having one cylinder connected on an automatic switch-over valve and he said they do leak gas so you must always have 2 cylinders connected.

 

I always thought that one side was disconnected if the other side was in use - apparently not 100% disconnected.

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1 minute ago, Alan de Enfield said:

We had an 'owners rental' gas check done on one of our static hire caravans recently as the legislation re switch over valves has changed (they MUST  now be fitted with an over pressure device) and I actually asked the gas-man about only having one cylinder connected on an automatic switch-over valve and he said they do leak gas so you must always have 2 cylinders connected.

 

I always thought that one side was disconnected if the other side was in use - apparently not 100% disconnected.

I think ours is an OPSO valve, and I seem to recall they suggest you change them every 10 years. I always have two bottles connected to ours. One bottle is always turned on at the bottle, and the other turned off. Its a simple matter to flip the switch on the regulator and turn the full bottle on when one is empty.

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1 minute ago, rusty69 said:

I think ours is an OPSO valve, and I seem to recall they suggest you change them every 10 years. I always have two bottles connected to ours. One bottle is always turned on at the bottle, and the other turned off. Its a simple matter to flip the switch on the regulator and turn the full bottle on when one is empty.

One of the reasons i looked was to check the age of the tails, in the excitement of seeing a changeover valve i completely forgot to do so :banghead:

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19 minutes ago, Hudds Lad said:

This is as close as i can get to what i recall it looking like, the bulbous bit in the middle and then a tap to the gas pipe underneath, but it was definitely red on top and not grey

 

That sounds like the one we ha don the boat with a "standard2 propane regulator attached, a bit like this one, but larger and simpler.

 

TPA Automatic Propane Gas Changeover Kit- With OPSO

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4 minutes ago, Tony Brooks said:

 

That sounds like the one we ha don the boat with a "standard2 propane regulator attached, a bit like this one, but larger and simpler.

 

TPA Automatic Propane Gas Changeover Kit- With OPSO

 

That little 'button' on the top (with the clear plastic cover) is the overpressure valve, so when the sun shines and the cylinders get hot they vent off the gas rather than exploding

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17 hours ago, Alan de Enfield said:

 

That little 'button' on the top (with the clear plastic cover) is the overpressure valve, so when the sun shines and the cylinders get hot they vent off the gas rather than exploding

 

Cobblers!

 

 

 

(The bit about venting off gas I mean. They don't "vent off gas".)

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1 minute ago, Alan de Enfield said:

 

Can you please exoplain then what it does - my 'gas man' explained it as opening and venting if the gas pressure in the cylinder got too high.

 

It closes if the pressure rises above a certain value (dunno what it is), and isolates the appliances from the over-pressure. This is because appliances are designed to be gas tight at 37mb, but not at the 2 or 3 bar that gets passed through if the regulator fails. 

 

Nor is there any more than a negligible risk of bottles exploding in the sun. The pressure of the fixed volume of gas is proportional to its temperature (https://en.wikipedia.org/wiki/Ideal_gas_law), and gas bottles are designed to be plenty strong enough to withstand heating in the sun.

 

 

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If the valve on Alan's regulator was there to prevent gas bottles exploding in hot sunlight, what protection would there be for all those full unused bottles stored in mesh cages out in the open at suppliers premises or on construction sites or on the decks of fuel boats and similar locations?

Edited by David Mack
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3 minutes ago, David Mack said:

If the valve on Alan's regulator was there to prevent gas bottles exploding in hot sunlight, what protection would there be for all those full unused bottles stored in mesh cages out in the open at suppliers premises or on construction sites or on the decks of fuel boats and similar locations?

 

Actually, all (proper) gas bottles have an emergency over-temperature pressure relief valve. Its that little amber-coloured plastic bung in the back of the brass valve. If the bottle gets dangerously hot it pops out and releases all the gas in the bottle slowly. 

 

But this never happens in just sunlight. 

 

 

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24 minutes ago, MtB said:

 

It closes if the pressure rises above a certain value (dunno what it is), and isolates the appliances from the over-pressure. This is because appliances are designed to be gas tight at 37mb, but not at the 2 or 3 bar that gets passed through if the regulator fails. 

 

Nor is there any more than a negligible risk of bottles exploding in the sun. The pressure of the fixed volume of gas is proportional to its temperature (https://en.wikipedia.org/wiki/Ideal_gas_law), and gas bottles are designed to be plenty strong enough to withstand heating in the sun.

 

 

 

Thankyou.

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14 minutes ago, MtB said:

 

It closes if the pressure rises above a certain value (dunno what it is), and isolates the appliances from the over-pressure. This is because appliances are designed to be gas tight at 37mb, but not at the 2 or 3 bar that gets passed through if the regulator fails. 

 

Nor is there any more than a negligible risk of bottles exploding in the sun. The pressure of the fixed volume of gas is proportional to its temperature (https://en.wikipedia.org/wiki/Ideal_gas_law), and gas bottles are designed to be plenty strong enough to withstand heating in the sun.

 

 

In a lpg cylinder (i.e. part gas, part liquid) is not the pressure something to do with the pressure at which the gas boils, which varies a bit with temperature? For example, around 10 bar at 20 Celsius for propane according to this chart.  https://www.engineeringtoolbox.com/propane-vapor-pressure-d_1020.html

A happy equilibrium is maintained - it not being a Boyle's law thing

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We've one of the auto changeover valves as described by Tony. I often only have one bottle connected whilst the Mt bottle is taken away and I find a calor supplier with bottles and/or open when  I can visit, anyway all I know is there is no discernable issue. No leaking gas or sucking in of air (huh ? ).    I dont tend to use the auto change over function as its handy to know the bottle is empty and I'm too lazy to switch both bottles on /off everytime I arrive/leave the boat but if we are on an extended cruise its handy to switch both bottles on and not have to worry about gas running out at an inconvenient moment.

 

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On 02/06/2023 at 11:31, MtB said:

 

Actually, all (proper) gas bottles have an emergency over-temperature pressure relief valve. Its that little amber-coloured plastic bung in the back of the brass valve. If the bottle gets dangerously hot it pops out and releases all the gas in the bottle slowly. 

 

But this never happens in just sunlight. 

 

Always assuming somebody who doesn't know what they're doing hasn't done a DIY refill from a big cylinder and failed to leave the required gas expansion space above the LPG... 😉

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I have a manual change over valve which has an L-port valve in the middle so it should be safe to run it connected to a single bottle. Why anyone world want to do that I'm not sure, unless one person was cooking while the other was out getting a fresh bottle. Having said that I don't always remember to turn off the connected bottle while I'm changing an empty. The L-port valve prevents any connected bottle venting to the disconnected port. 

 

I suppose any valve can leak tiny amounts of gas if a port is left unconnected, but as it's all in a gas tight locker that vents at the bottom that shouldn't really be a safely issue. If the auto changeover valves really leak more significantly with one bottle connected as someone has suggested, then they're not fit for purpose. I somehow doubt that's the case unless they're well past their expiry date.

7 minutes ago, Paul C said:

Don't you mean "I'm sorry for posting false information on the forum" - or are you too much of an arse not to admit to this and own up, for the greater good?

 

Does every poster that gets something wrong really need to make a full apology now? This forum is getting like the media demanding mea culpas.

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13 minutes ago, blackrose said:

 

 

Does every poster that gets something wrong really need to make a full apology now? This forum is getting like the media demanding mea culpas.

 

Of course not. You can take the approach of just saying something vague like "thank you" or flat out denying you said something, or something happened, or plain old lying if you want.

 

But it doesn't do your reputation any good, if you simply become tarnished with an "untrustworthy" or "attention seeking" or "posts for the sake of posting" label, instead of just saying something like "woops - sorry" or whatever. Its not a complicated word to say. And it also makes everyone reading have to filter out the crap from the actual, useful stuff on a forum so it just dilutes its ultimate value more and more.

 

Of course, you may posture any posting style you like, I am not the arbiter of it. You yourself are responsible for your own words.

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35 minutes ago, Paul C said:

Don't you mean "I'm sorry for posting false information on the forum" - or are you too much of an arse not to admit to this and own up, for the greater good?

He posted information he was given in good faith, someone corrected him and he said thank you, sounds hunky dory to me

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