Pressure Valve Dispensing

Hello fellow printers,

I am currently working on a silicone-based printer and am rather new to the whole subject of RepRap and printing, especially the programming side of it.
I was wondering if anybody here would be able to help me.

There is a problem I have, I want to actuate a dispensing-valve with air pressure and for that I am thinking to use a 3/2-valve that gets its signal from the RAMPS-board. Since I don't use any fans I thought about using the fan-signal (12V instead of 5) to trigger the valve. As I mentioned before, I have little experience in programming the board, is there anybody that could help me set that up?
I know about the different M-codes, but where exactly would I put one of these to turn the fan (and therefore the valve) "ON" every time I use the extruder? (So basically using the extruder-info to power the dispensing-valve)

I hope you guys understand what I mean, since this is a rather new topic for me I might have a little problem articulating myself in it.

I'd be happy for any help you can give me.

Thanks

Nordish

From what I understood, you want to control silicon flow while moving the print head.
A pressure valve is not fast enough to be used in pulse_width_modulation (PWM ). So I think, this aproach is a dead end street.
Except you only want to place dots of silicone on predefined places.
Most people control their "syringe"-style extruders by a leadscrew and ( geared ) stepper motor. That way the syringe would really work as an extruder.

The gcode to control the printer is stored on a local SD-card or sent by a PC through USB connection. With terminal programs like "pronterface" you can also send single ( M- ) commands.

Thanks for the reply.

So how would I go about getting a 5V PWM-signal into an 12V ON-OFF signal? So that i can "grab" the info for on/off from the RAMPS-board and actually turn on the dispensing valve using that info?