Electronics controlled valve for cooking gas bottle?

[Faringdon]

Hi,

We are designing and building  cooking gas bottles with electronics controlled 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.
{EDIT...word "kids" used....it wont actually be for use by  children whatsoever. END OF EDIT}

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, if i may:
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.

[jpanhalt]

Have you searched for brushless DC motors?  Quite common today.  One of my first search hits was for brushless fuel pumps.  There are also brushless servo motors.

[pcprogrammer]

Search for "automatic gas valve" or "automated gas valve". No need for a motor since a lot of these use a solenoid.

As an example: https://www.aliexpress.com/w/wholesale-automatic-gas-valve.html

[Berni]

The easiest way to get high torque motor out of the box is a RC servo motor.

They have plenty of torque to turn a valve and even have the control electronics inside. All you need is to give it a typical 1 to 2ms RC servo pulsetrain from a MCU pin and it will turn to the position you want. If you also want to sense the motor torque then place a shunt resistor in the ground wire to the servo to measure the motor current. The harder the servo is pushing towards the desired axle position the more current it will send trough the motor.

This of course works for things like ball valves that only turn 90 degrees. But if you are turning the valve that is directly on the tank (those typically need like 4 to 7 full turns to actually open and close), then you can modify a RC servo for continuous rotation (or buy a servo already built for it). Those can keep turning round and round, however they can no longer be moved to a precise angle anymore, so you would have to watch motor current going up when the valve gets to the end.

[pardo-bsso]

What's the maximum pressure? (I assume this goes before the regulator)

Look into any industrial depot, even GNC car onversion shops. That's a very common valve.

[capt bullshot]

I'd recommend to have a look at the design of gas safety valves, common with all kinds of gas stoves etc. Afaik, these work with a thermocouple and a solenoid, or just plain mechanically. Then try to think which way one can modify the electrical circuit of a thermocouple driven solenoid to add your desired function without breaking the required safety features.

IMO designing a completely new gas valve is the wrong way.

[Faringdon]

Afaik, these work with a thermocouple and a solenoid

Thanks, I wonder if that is why ATEX approval would be needed?...that is, if you dont have the thermocouple to detect no heat (therefore flame gone out and gas potentially spewing out and being an explosion hazard).....is that why ATEX approval would be needed?

[SmallCog]

I’d use a quarter turn ball valve (one that’s suitable for gas usage)

Drive it into the open position when a token goes in, just before time expires warn the user and if they insert another token leave the valve open, otherwise drive it closed.

I don’t know your gas regulations but hopefully using a mechanism like the below to actuate an approved valve satisfies them

https://www.ebay.com.au/itm/224601175506?mkcid=16&mkevt=1&mkrid=705-154756-20017-0&ssspo=uVJdG9zsT1y&sssrc=2349624&ssuid=fd5nzGNrSmq&var=&widget_ver=artemis&media=COPY] [url]https://www.ebay.com.au/itm/224601175506?mkcid=16&mkevt=1&mkrid=705-154756-20017-0&ssspo=uVJdG9zsT1y&sssrc=2349624&ssuid=fd5nzGNrSmq&var=&widget_ver=artemis&media=COPY[/url]

[capt bullshot]

Afaik, these work with a thermocouple and a solenoid

Thanks, I wonder if that is why ATEX approval would be needed?...that is, if you dont have the thermocouple to detect no heat (therefore flame gone out and gas potentially spewing out and being an explosion hazard).....is that why ATEX approval would be needed?

I can't answer that - I suggest asking an expert (I'm not an expert for ATEX and related stuff). Guessing and asking random people might be fine for marketing purposes, but isn't a recommended way to do safety / certification engineering stuff.

[jonpaul]

Compressed propane gas...electric valve..custom built....consultant...consumers use..

Recipe for a liability lawsuit

suggest

Obtain 1..10M £ liability and EO insurance

retain lawyer spécialiste in consultant liabilities défense

Rethinking the job benefits and cost

Jon

[Ground_Loop]

Normally, I avoid preaching safety as most of it is self evident and don't feel a need to stoke my own ego by saving others from themselves. But I digress. Anyway, I've done controls in flammable environments and there are two basic requirements for sensors and safety devices. All circuits must be intrinsically safe (24 VDC or less and 100 mA or less) and all safety devices must be hard wired (no programmable devices in the circuit path). There are exceptions such as certified safety controllers, but you don't have one of those.

[tggzzz]

We are designing and building  cooking gas bottles with electronics controlled 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.

Flammable gas + electricity + homebrew electronics + kids + the king of reliable SMPSs.

What could possibly go wrong?

[tggzzz]

Afaik, these work with a thermocouple and a solenoid

Thanks, I wonder if that is why ATEX approval would be needed?...that is, if you dont have the thermocouple to detect no heat (therefore flame gone out and gas potentially spewing out and being an explosion hazard).....is that why ATEX approval would be needed?

I can't answer that - I suggest asking an expert (I'm not an expert for ATEX and related stuff). Guessing and asking random people might be fine for marketing purposes, but isn't a recommended way to do safety / certification engineering stuff.

It is remarkable and noteworthy that needs to be said.

I would be amazed (and pleased) if the OP took any notice whatsoever

[tggzzz]

Compressed propane gas...electric valve..custom built....consultant...consumers use..

Recipe for a liability lawsuit

Agreed.

Normally I'm not someone that bothers unduly about safety (brought up a kid with a 6ft vertical hole in the kitchen, backpacked together around India in early teens, solo pilot making forced landings before able to start to learn to drive a car, etc). I certainly hate ambulance chasing lawsuits, especially where the victim wasn't paying attention or doing something silly such as walking into the road looking at their phone.

But in a case where there would have been planned negligence by someone with Dunning-Kruger syndrome, I would definitely use a good lawyer and the legal system to its fullest extent.

It wouldn't bother me if the perpetrator was "a man of straw" and not able to provide restitution; sometimes visible punishment is necessary pour encourager les autres.

(Other example: an idiot with a laser blinding an innocent person passing by)

[Terry Bites]

Sparks gas sparks gas sparks gas. mmmmm. Kids at camp whoa! 
Are you "gas safe" registered and do you infinite personal liabilty insurance and afford best lawer in the land? [no, not your cousin]
Don't even think about it.
Its illegal to fit one yourself even if you buy a ready made electric valve system off the shelf.
Permitting or encouraging a an unregistered person to work on gas is also a crime in the UK.

Grieving parents can be a real pain and you're too young to do years of jail time. You probaly won't get do do the time though, the parents will string you up first.
Believe!!

[pcprogrammer]

We are designing and building  cooking gas bottles with electronics controlled 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.

At least they (OP used "We") are aware about safety

And fortunately they are designing and building the complete thing, gas bottles and all, so it must be ok

In itself it is not to dangerous when an approved "automated valve" is used and the installation is done by a professional gas fitter. Risk on leaks should then be minimal and an approved "automated valve" should be guarded from making sparks. As long as the electronics is not in the same enclosure as the gas bottle and the wires are fed through a proper guide the risk will be minimal.

But still be very aware of any liability. And like tggzzz pointed out, to us, here on the forum, your (Faringdon) reputation is not one of being very capable.

[AndyBeez]

I'm not sure of the 'code' in your locale, but my 50 centrinos...

Your design MUST be failsafe off - if the power fails or the STM32 crashes, the valve shuts both automatically and mechanically. There must never be a latching action.

Your design must be tamper proof; say some 'bright spark' kid realises the gas can be left on by removing the battery, which would have been me at that age? Maybe all parts should be kept in a locked cage?

Your design should not be activated by interference from any other EM field - such as wifi, mobile phone or even CB radio. Metalic shielding of the uC is needed.

Your design should be safe in storage - there should be no egres of gas from the valve if the mechanism if unused for months. The battery should also have enough capacity to remain unattended for long periods.

Your design will need to be both certifiable and insurable.

+ Why bother with a token and the token's mechanism when you could use an app over Bluetooth? It's what 'kids' expect these days.

[geggi1]

I'm enough familiar with ATEC and IECex to probably give you some sensible advice.
First. of all it is going to be expensive.
Second. you would be able to build this with off the shelf components.
Third. get familiar with the IEC 60079 series of regulations.
Fourth. If you decide to build its probably best to use Exd components.

[NiHaoMike]

Unless the cooking process needs an open flame, how about use an induction cooker instead?

[tooki]

OP said it’s for a kids campground. Shouldn’t they be cooking on campfires?

[floobydust]

Who charges kids by the 10 minute interval for cooking while camping? The premise seems ridiculous, just buy your own bottle.

OP, you're in way over your head again and the cute story about it being for "kids" seems to be a larp.

A lot depends on how many BTU the burner is. There's a pressure regulator, usually redundant dual shutoff solenoids for safety according to gas standards. The electronics has a functional safety requirement for the hardware and firmware as well. You've said nothing about the ignition system and flame detect, where it's being used etc.
You need to meet the gas safety codes as well as hazloc, a professional engineer assesses the hazardous area and classifies accordingly. Not to your economical whim.

[Faringdon]

Thanks for all these, i will look into all this....BTW, it will need to be "generally safe"....the people who use this will get a demo of how to use it safely....they are trained people.......it will likely also have manual turn on/off valves aswell, and when these are used properly its perfectly safe...
There wont be any lawsuits. Thats all i can say. This just needs to be designed to be safe to  "people behaving sensibly with the kit"....and...."people who use it in accordance with the instructions".

[jonpaul]

thought experiments

Valve or control fail ON, uncontrolled gas
Gas on, flame out
Child is burned by stove

We consulted  on surgical lasers, illuminators MRI,

We insisted that our Customers signed a liability / hold harmless agreement before acceptce of order.

jon

[exmadscientist]

Screw this one up badly enough and you get a nice explosion.

cooking gas

electronics controlled valves

kids

purely a safety feature because its kids

valve which is opened/closed by a small motor

ATEX

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

"generally safe"

demo of how to use it safely

trained people

manual turn on/off valves aswell, and when these are used properly its perfectly safe

There wont be any lawsuits.

"people behaving sensibly with the kit"....and...."people who use it in accordance with the instructions"

Please stop. Please. Just. Stop. I'm aware of your reputation but I'm going to say this anyway, "pour encourager les autres".

Do you know what "foreseeable misuse" is? Because this has a "foreseeable misuse" disaster lawsuit written all over it. When your device fucks up and starts spewing fuel into the air randomly because of a foreseeable mistake, and somehow it ignites (or even doesn't, it doesn't really matter), no one is going to touch that manual shutoff. They are going to run away. I know because I've been around "small" propane tank fires. You have no idea what you are doing or how many people you could kill (though it's decent odds you do know how many people you can troll).

Just stop this insanity now.

[gbaddeley]

All token & coin & free timer based cooking facilities that I have seen are electric. Eg public hot plates / BBQs in parks and camp grounds, even if gas is in nearby buildings for hot water etc. The reason is SAFETY. Gas is very dangerous if anything goes wrong with the token system or valves, hoses, burners.