rc servos are great, they come in many varieties. brushed motor or brushless, plastic, metal or titanium gear. different reaction speeds and torque ratings. might sound a little complicated but its not really, its all just a price thing - more expensive servos tend to be stronger and quicker and to make them stronger they put in metal or titanium gears.

i could only see one potential problem with using rc servos. i can tell you from experience that a servo pushing against an imovable force will burn out its internal driver board. for example, if you had one attached to a valve and your control circuit was calling for the servo to open the valve. if your program was not calibrated right and was getting the servo to try and turn the valve passed open(assuming the valve has a stop) the servo wont last long, you can count on that.

if you go down this route you will need some sort of spring loaded coupler. if the valves are nice and loose then this is no biggie.

this is a typical rc 'servo saver'
http://www.rc-area.co.uk/blog/wp-con...ervo-Saver.jpg
you will see in the pic two cams pressed together by a spring. the spring tension is adjustable. in your application i guess the servo would attach to the top,black, part(you can see a lever on the back of it) and then some linkage from the orange part to the handle on your valve.

there is a simpler design http://news.killerhurtz.co.uk/servo_saver.jpg but its hard to explain how it works. you have to see it in your hand.

if you got something like this in your design you would have no problems, except for programming the PIC. i might be able to help you out by getting some specs for controlling the servos. i can tell you now that they are three wire, most are max 6volts but work away quite happily at 5volts.
i cant remember if it is PCM or PWM they use. anyway, if you need info i might be able to help.

a decent rc servo will cost £80 -£100. really good ones even more. £40 - £80 will get something reasonable but stay away from anything cheaper unless you read good reviews about them.

btw, do you think there will be much lag between the valve opening and the flame shooting up in the air. if there will be some lag, like half a second or more then it might not look right. imagine a nice loud kick drum beat hitting you and half a second or more later the flame shoots up out of the stage. im just saying it might be something to consider.