Cooking gas bottle valve controlled electronically

[Flyback]

Hi

We are designing and building cooking gas bottles with valves. These are for kids camping chalets. Its purely a safety feature because its kids. As you can tell, there is no big market for this product, its just to get these kids out camping.

System description:
So we have a bottle of cooking gas with a valve which is opened/closed by a small motor. The valve assembly sits on top of the gas bottle. The kid inserts a token (like coin) into a box, and then they get the gas valve opened for 10 mins, then closed again, until another token is inserted. The token box is near to the valve box and is electronically connected to it via a small cable. Which passes though the enclosure walls.

A STM32 micro in the valve assembly contols the valve motor. The micro will be sent to sleep whenever possible. The power to drive the motor comes from a small lithium cell with cell voltage of ~3.6V. There are no SMPS’s in the product. (because we need standby power to be very low). The motor is simply driven directly from the battery. (FET switch, switched by micro). The battery is non-rechargeable, as these have lower leakage current and last longer. The battery voltage is flat at 3.6V for most of its cycle..therefore we cant use battery voltage to sense when the battery is flat. So we intend to do some kind of coulomb counting.

Because its gas, the valve assembly product needs ATEX approval.

When the motor has fully closed (or fully opened) the valve, we don’t want the motor drawing any power, so I guess we need some mechanical latch in there. We can’t use a latching solenoid valve as they draw too much power in operation and in standby. They draw a high current when first actuated, and the ATEX approval means all our currents need to be well limited.

We need to sense when the motor has got to the end position where the valve is fully closed (or fully open)…We are thinking of doing this by sensing the motor current..because when the motor hits the end stop, then its rotor will cease rotation, and thus give no back EMF…so the rotor current will suddenly increase….we will detect this so as to tell us when the motor has reached the end stop.

..However, we were also thinking of adding a double check to this, by way of a Hall Sensor stuck to the rotor…so we can check the motor really has got to the end stop…after all, the user may somehow yank it so the motor stops in the wrong place (valve not fully open/closed). We are also worried that the user may try and somehow force the valve to be always open (so they can get more gas)

Questions:
1..What type of motor do you think can be used for this? (we aren’t finding such low voltage motors for this). Presumably DC motor is a no-no due to brush sparks and the gas (ATEX approval needed)?
2..Do you know of any kind of existing product on the market anything like this?…even if its not for cooking gas….…we cant find any.
3..Do you have any ideas for low-bias-current current limiters that we will need due to the ATEX approval?
4..Why dont normal gas cookers need ATEX approval?..they must have electronics in them.

 

[Inquisitive]

Question: In the event of an emergency or circumstances uncommon or beyond control can this be overridden and closed in an emergency. (eg, leak is discovered, fire from incorrect orifice) Remember when making things idiot proof the idiots can get very creative.

 

[shortbus=]

4..Why dont normal gas cookers need ATEX approval?..they must have electronics in them.

But not in the valve. I can't imagine any electric motor controlled valve getting approved. Why concentrate on the bottle valve? Most bottle valves are turned on and left on until they are empty and need changing.

I've never run across a gas bottle/tank valve that could be turn with such a small powered motor. A valve that easy to turn would leak around the valve stem.

 

[Flyback]

Why concentrate on the bottle valve? Most bottle valves are turned on and left on until they are empty and need changing.

Thanks, its because when the token has "run out", the gas bottle valve can be shut off.......and when necessary, the entire gas bottle and valve can be sent back to the depot to be re-filled...and given any maintenance. The gas bottle may have to be returned to depot when its still got gas in it...so valve needed. The customer pays for the gas, and when their token runs out...they are not allowed to use any more gas from that bottle....unless they insert another token.

I've never run across a gas bottle/tank valve that could be turn with such a small powered motor. A valve that easy to turn would leak around the valve stem.

Thanks, we coudl use a gear system...and do it liek that...then the low power would be ok.....it woudl just take time to shut off the valve.

I can't imagine any electric motor controlled valve getting approved.

Thanks, but if solenoid valve can get approved, then why not electric motor valve?

But not in the valve.

Thanks, though the motor would be kind of separate to the valve.....and i dont believe motors cause sparks anyway.

Also, i cant see why our system would need ATEX (Atmosphere explosive) approval?...most gas cookers have a sparker to light the gas anyway?

 

[For The Popcorn]

You might look at Orbit valves for garden hoses. I don't remember exactly what the mechanism looks like but they use some kind of solenoid to control the flow of water. Pulse it briefly with one polarity and the valve opens. The other polarity, and it closes. No power is required to maintain its state.

But the idea seems very complex compared to a standard (usually disposable) propane cylinder. Those cylinders have a valve that is closed when the cylinder is unscrewed. There's little danger the cylinder will leak when it's unscrewed. No need to attach some kludgey mechanism that may fail when the cylinder is refilled or an expensive valve/coin assembly lost or stolen in the prrocess.

 

[rjenkinsgb]

Consumer gas cylinders in the UK have a kind of tool-less quick release fitting - effectively something like an an overgrown tyre valve style but groove lock rather than thread, where the valve operating mechanism is on the regulator that attaches to the cylinder.

They are different dimensions for butane and propane cylinders but the same principle.
(Industrial propane cylinders have a screw in fitting, similar style to acetylene & oxygen welding cylinders).


These tool-less fittings would be an ideal candidate for a powered valve operator - it only has to operate the pin plunger in the regulator or attachment, that presses the valve stem in the cylinder neck. A small motor operating a cam, with limit switches to control the end travel, would be simple.

The normal manual ones have a rotary lever to operate the plunger; fully anticlockwise releases the latch that attaches it to the cylinder, centre is off and fully clockwise is gas on.

Gas bottle regulators guide | Flogas

Not sure which propane regular you need? Want to learn how to use a gas bottle regulator? Read expert advice on gas bottle regulators here at Flogas.

www.flogas.co.uk

Nothing changes on the cylinder so it does not matter what suppliers cylinder you use, as long at it's the appropriate gas type so the attachment diameter is correct.

See page 8 on in this for the bare valves:

Category: LPG Valves and Tank Equipment | Cavagna Group UK

Cavagna UK can offer the full range of LPG valve and tank equipment.

cavagna.co.uk

I cannot see any supplier accepting modified cylinders; the safety devices for excess flow, overpressure and overtemperature etc. (internal plus sideways the stub on the valves in the pictures below) are built in to the cylinder section of the overall valve so that's presumably related to the testing and approval requirements, and the valve must also open simply for refilling and be idiot-proof.

("Patio gas" is a name for consumer propane, to distinguish it from industrial screw-fitting cylinders).

 

[rjenkinsgb]

Also, i cant see why our system would need ATEX (Atmosphere explosive) approval?...most gas cookers have a sparker to light the gas anyway?

If something goes wrong with an LPG cylinder valve, eg. if the cylinder gets knocked over and the valve cracks, it can release kilos of liquified gas in seconds.

A slow leak in a confined space can have the same effect, eventually, as LPG is significantly denser than air. Natural gas is methane and does not accumulate so easily as it's less dense than air.

In other words, LPG cylinders are fuel-air explosive devices, waiting for something to trigger them.

Thermobaric weapon - Wikipedia

en.wikipedia.org

Appliances are fed by pressure regulators and at far lower pressures than in gas cylinders, approx. 0.25 PSI.
No liquified gas.
Leaks in domestic (non-LPG) gas appliances are a rather lower grade hazard by comparison to LPG.

ps. I hope you realise that you would have to make your system so it can only be used with appliances that have flame failure and tilt cutoff?

If some idiot kid inserted another token just after the previous one had expired, thinking the burner was still alight because it was hot - but it had actually gone out - your gadget could be responsible for gassing the users, or blowing it up when the gas reached another ignition source.

Make sure you have good liability insurance!

 

[Flyback]

Thanks,
Also, a gas cooker needs (and permits) a spark to be used to light it.
As such, how can it possibly ever pass ATEX approval?
Do you agree, ATEX approval and gas fires can never happen?

 

[For The Popcorn]

Does it really matter if anybody on a random forum agrees or not?

 

[rjenkinsgb]

ATEX is certification for things that are safe to use in an explosive atmosphere.

Among other things it covers such as tools, which must be non-sparking alloys and electrical equipment that cannot generate a spark where the external atmosphere can penetrate or come in contact with a spark.

Gas cylinders can inherently leak small amounts of gas as fittings are connected or removed and I can easily see that filling equipment / filling sites could have large amounts of free gas in the atmosphere.

Cylinders & valves etc. needing approval makes sense, as explosive atmospheres are possible.

Gas cooking and heating appliances also require safety approvals, but whatever that is it cannot be ATEX.

 

[Flyback]

Cylinders & valves etc. needing approval makes sense, as explosive atmospheres are possible.

Thanks, yes indeed they are possible...if flame goes out and the gas keeps going...but there is nothing stopping someone trying to light the gas out of the cooker.......so in the customer house, when the cylinder will be next to the cooker, ATEX approval seems not right somehow?

 

[danadak]

One thinks, like in medical injection pumps, of using a dual core processor to
manage a system like this, as well as multiple gas sensors to insure safety.
One processor checking on the other. To reduce control system induced
errors.

But mechanical valves with solenoids, ones especially where they "sit" for long
periods of time unused in general environment, very sketchy I would think. Question
to industrial designers, are servo driven ball valves considered more safe than
solenoid driven gate valves ?


Regards, Dana.