hello the three different types of machine torch - info req

Problems and questions
1

so I gather there are three differnt types of machine torch.

pt31 lg-40
http://www.ebay.co.uk/itm/New-20073-PT-31-LG-40-Air-Plasma-Cutting-Straight-Machine-Torch-Head-Torch-Body-/251467483245?pt=LH_DefaultDomain_3&hash=item3a8ca1486d

non pilot- arc = no good for cnc as require the arc to jump onto the work surface to start, so need clean metal and correct torch height = no good
???

whats an sh-4 then
http://www.ebay.co.uk/itm/SH-4-Plasma-Cutter-torch-head-SH-4-Machine-torch-body-plasma-consumable-/130603773495?pt=LH_DefaultDomain_3&hash=item1e68976e37
???

so I take it a sg-55 is a pilot arc? arc starts in the torch head ? contstant
does this mean no good for cnc either due to the constant arc or high frequency starting pilot?
http://www.ebay.co.uk/itm/SG-55-AG-60-Plasma-Cutter-plasma-cut-machine-cutting-torch-60A-12Feet-JW514-/130617608658?pt=LH_DefaultDomain_3&hash=item1e696a89d2

???

P-80, these look similar to the sg-55, so can I simply assume they are pilot-arc
but for thicker steel or are they moving electrode - blowback torches - i.e. that is the difference, ideal on cnc?
http://www.ebay.co.uk/itm/P-80-Plasma-Cutter-plasma-cutting-Machine-Torch-Head-0-machine-torch-torch-body-/130618439130?pt=LH_DefaultDomain_3&hash=item1e697735da

basically I want a cheapo torch to fix a rack and pinion system to like this
http://www.ebay.co.uk/itm/Plasma-cutting-machine-torch-cutter-robot-robotic-cnc-/271468789891?pt=LH_DefaultDomain_0&hash=item3f34cd0083

[ a moving, spring loaded electrode in the torch) - blowback


do I simply opt for the expensing blow-back system, can I get away with the p-80 pilot arc?
thanks


ahh I get it now
-Blowback style (non high frequency start) torches will transfer an arc to the plate from a fair distance (my Hypertherm Powermax45 will transfer from 1/4" away from the plate). This long transfer distance allows for best plate piercing capability in a mechanized application…by allowing the torch to stay back at a good pierce height which allows the pierce spatter from hitting the torch nozzle orifice…which cause nozzle wear and poor cut quality. The pilot arc also allows for rapid starts on rusty, scaly, or painted materials. Firing the pilot arc in the air will cause nozzle orifice erosion…and should not be done often.

so i need a blow-back machine torch. - great
does anyone make one with a rack and pinion housing

2

I’m no expert but as far as I know you need the correct type of torch to suit your plasma power source. A blow-back torch won’t work on an HF start system and vice-versa.

I have only used one blowback style system ( a small Miller unit) and it was quite unreliable, often not starting.

3

A universal torch like the Thermal one torch will work on high freq, and blow-back systems . It would be considered a blow back torch style with the start cartridge setup. Sometimes it will need a spacer to lock down the cartridge in high freq setups… Works well in High freq applications.