Motorised gas valve for cooking gas bottle?

[boilerboy22]

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.

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.

 

[PETE 123]

I would just go electric with a pre payment meter.
Or common cooking area. if possible.

 

[Ric2013]

Clockwork mechanism?

I can remember the days of a 50p coin in the meter, so a similar product must have been made at some stage (although that was natural gas, not LPG).

 

[ShaunCorbs]

Solenoid valve

 

[boilerboy22]

Thanks, i am being told that solenoid valve wont pass ATEX approval (atmospheres explosive). You see , we dont have the thermocouple (flame out) detector..so we therefore need ATEX approval. Solenoids draw too high current when compared to motor valves...and high currents arent allowed in ATEX circuits......so motorised valve must be used....since you can use gearing and make it low current for long time, type of thing.

 

[Ric2013]

Is ATEX relevant in this context? I thought that was for ATmospheres that are EXplosive (works much better in the French language), such as when working in rooms full of gas, oil rigs and the like, not for a gas valve in a camping chalet?

 

[boilerboy22]

Thanks, yes, though if the flame goes out.....and you dont have thermocouple flame out detection...then the room can get full of gas.

 

[Ric2013]

Thanks, yes, though if the flame goes out.....and you dont have thermocouple flame out detection...then the room can get full of gas.

Same goes for my kitchen stove. You can leave the gas taps on, and it has all sorts of electrical gismos incorporated that can and do spark. Only FFD is on the oven. Though in fairness I expect that it's running on grandfather rights and modern ones do have Flame Failure Devices and hence that would be the answer to Q4.

If the FFD is not required so long as there is no risk of an accidental spark, then I still think clockwork mechanisms are a great idea. Unless, of course, and I suspect you'll find this is the case, the FFD is required for any indoor gas appliance now? If yours fails shut after ten minutes and were clockwork, I don't really see how that is any less safe than the portable gas cookers with a single gas ring and a piezo-electric ignition as there is no electric motor to spark and the self-closing nature at least limits how much unburnt gas can escape in total. That said, I appreciate that the instructions for portable gas stoves invariably have some kind of anti-lawsuit clause that means they MUST be used outside and never in a chalet (which will often be ignored) and you want one that genuinely can legally be used indoors.

The problem I have, however, is the concept of a timed meter. It's an unfair measure of consumption. On my 1940s paraffin stove I only really have high flame as I need to run it fairly hot. The advantage of gas is that it burns cleanly with a low flame, but you'd charge me the same as for a high flame? Or what if I'm 30 seconds away from a boiled kettle - I have to pay for 9.5 minutes of unused gas?

What if you locate a coin or prepayment card gas meter outside of the ATEX zone? Top up by £5 and get a refund on unused credit when you leave kind of thing. Would that meet the rules? The gas stove doesn't need to be portable anyway, and I'm imagining the gas bottle will have to be stored externally anyway.

 

[Ben-gee]

The problem I have, however, is the concept of a timed meter. It's an unfair measure of consumption.

The OP is not using the meter as a charging method, it is simply a safeguard against a large build up of gas should the children accidentally leave the gas on or unattended.
Think of it like a pneumatic light switch.

 

[snowhead]

I can't see there being any market for this product.

Has this product design been commisioned by someone/ some group or is it just an idea someone within the company / design group thinks may be successful?

The cost of long term testing in many environments and independent certification will wipe out any potential recovery of costs let alone profit.

No adult in charge of any kids is going to be allowing them to use any gas appliance unsupervised unless they are confident in their abilities, in which case thay won't need this type of device.

10 minutes is more than enough time to to release enough gas in a chalet to either be explosive or to asphyxiate anyone within it.

 

[king of pipes]

There are plenty of gas interlocking systems on the market I used to fit them in school laboratories and kitchens , with technology in solar power and battery storage I would think one of these systems could be adapted to be used in even the most remote of locations ?

 

[boilerboy22]

Thanks, but we cannot use solar or external battery....we only have the internal battery in the "pay as you go" valve which is connected to the cylinder.

 

[Knappers]

I think your criteria are too restrictive.
A latching solenoid is what you need but don't know if you'd find one to work on 3.6v - it's just not enough power. Then you'd need to control it and anything electrical would likely want 5v.
The only thing I can conceive would be to use a control valve with flame supervision (thermocouple) and use the battery circuit to energise the coil.
Insert coin and manually set valve, when timer ends valve drops?...
Search -

Gas Control Valve Tap with Flame Supervision Device​

 

[boilerboy22]

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? (Atmospheres explosive regulations)
Do you agree, ATEX approval and gas fires can never happen?

 

[Knappers]

Will only apply to equipment in cylinder enclosure or confined enclosure. Cooker would be in a ventilated room?

 

[Knappers]

Forget the spark - you'd have an open flame.
Of course you can't have a fire in an explosive environment!

 

[boilerboy22]

Thanks, im baffled why the customer has said they need ATEX approval. I think its because the flame could go out, the room could then get filled with gas, then the flame or spark happens, and then boom....but does that situation call for ATEX approval?

 

[Knappers]

assume theyre looking at a solution to fit onto gas bottle in enclosure and so nothing to do with fire. I would give up on having a bottle mounted solution and rather offer an inline solution to be mounted outside enclosure.

 

[boilerboy22]

I would give up on having a bottle mounted solution and rather offer an inline solution to be mounted outside enclosure.

Thankyou very much, that sounds good, though our customers may rip the tube off the cylinder and then put their own tube on the cylinder and steel the gas without paying.
Though your idea does sound very good.....we still need the motorized valve or latching solonoid which draws no power once it has been actuated. And this must be battery operated.
In your opinion, would you say we are looking at a custom valve etc?.....it all seems very expensive?

This is like what we seek...

Cylinder Smart Meter Interactive

www.paygoenergy.co

....but we dont want mobile phone control...just tokens inserted for 10mins of gas....and we need it battery powered, and with the "no power drain once valve actuated").

 

[Ric2013]

Thankyou very much, that sounds good, though our customers may rip the tube off the cylinder and then put their own tube on the cylinder and steel the gas without paying.

Also, they could even supply their own tube and regulator and bypass any fitting you come up with. In which case, then find a device that uses the small cylinders that cost a couple of pounds each and if they go through a whole can in a short amount of time, questions can be asked. But, realistically, a customer that supplies their own tube to save money on gas is likely to be a rare event, and I don't see how you can really avoid that.

From a liability point of view, I expect it's a bit like expecting a landlord to have a plan for when a tenant removes the gas hose from the gas cooker and just uses the open hose to toast his sandwiches. I grant that you are dealing with minors here, but I think what it's going to come down to is either they are considered mature enough to be safe to use the appliance (and someone takes ultimate responsibilty for them) or I suspect they would need to be supervised at all times.