safety shut down system help

[Phayilboy]

I am trying to create a safety shut down system for a project that I am working on. part of the system powers a motor which opens and closes a valve and I need a secondary circuit which monitors the main systems power level and then, sounds a buzzer and closes the valve when the main systems power supply fails. I have no idea how to do this so any help would be much appreciated.

 

[crutschow]

What is the power to the motor: AC, DC, voltage, current?

Do you need the secondary circuit to be battery operated (independent of any mains power)?

 

[Phayilboy]

Okay the power to the motor is DC (powered by a 7.4v 610mAh lithium polymer battery) yes the second circuit does need to be battery powered

 

[JimB]

I am trying to create a safety shut down system for a project that I am working on. part of the system powers a motor which opens and closes a valve

I guess that this is not very big if it operates from a 7v battery.

I need a secondary circuit which monitors the main systems power level

Define what you mean by "power level"
Supply voltage present?
Supply voltage greater or less than some specified value?
Motor current greater or less than some specified value?

and then, sounds a buzzer and closes the valve when the main systems power supply fails.

What happens when the shutdown system power fails?

As far as closing the valve on power failure, why dont you select a valve which needs power to open it, power it from the pump supply, then when the pump power fails, the valve will close.

JimB

 

[Phayilboy]

Yes you are correct this is not very big. When I said "Power level" what I meant was whether or not the supply voltage is present. I did not think of doing it like that because we need valves where by we have a large amount of control (more than just open/close) and also there will no pump because the valve sits at the head of a pressurised gas canister.

Phayilboy

 

[JimB]

What sort of a half baked project is this, some junior school kiddie science project?

You tell us that you want to shut down when there is no power to the pump, but, now there is no pump!

There is a pressurised gas canister, what the hell is that! A CO2 cartridge for a soda syphon or a 30kg cylinder of propane?

In the real world where things can go with a big bang:
You dont use proportional control valves as a safety shutdown valve.
Valves fail to the safe position on power failure, so if the safe position of the valve is closed, it closes, if the safe position is open, it opens. All without external power electric, pneumatic or hydraulic.

If you want help, ask the correct questions and tell what is really there, not just half a story, most of which is wrong.

JimB

 

[Phayilboy]

What sort of a half baked project is this, some junior school kiddie science project?

You are right in thinking it is half baked but we are in college not junior school

well we are trying to fit a flame thrower to the back of a large (about half the size of a go kart) we have all of that done and we are fuelling it with small propane or butane canisters (the sort of thing you put in a blow torch) when we tested it last week the battery powering the servo motor used to open or close the valve ran out leaving the valve open and emptying the gas canister. this was when we realised we needed to have some kind of safety shut down system in case this happens again.

You dont use proportional control valves as a safety shutdown valve.

perhaps then like you suggested a valve that shuts down when there is no power could be added to the line. that aside how would I create the circuit to sound the buzzer when the main system power is no longer present?

I am trying to give as much information as possible but this is a group project and as it is i am having to keep phoning people to get information about how the current system works.

Phayilboy

 

[KeepItSimpleStupid]

Generally the safety system should be separate. Example: an air actuator might be used on the cylinder ( I did this with 3600 PSI cylinders). If there was a fire in the gas cabinet the polyetelyne hose would burn and the valve would shut.

Gas monitors and possibly temperature sensors should enable the main gas valve. The SI (safety instumented) system should probably be separate at this point. The control valve can be separate. If you can install a flow limiting orifice in the line it's possibly better than an excess flow valve. At least that's what we found after accident investigation. The excess flow valve failed and the operator though the HYDROGEN TANK WAS EMPTY, it wasn't. An operator made a decision based on an empty tank and boom! We had a room to clean up and an investigation to do.