SL 40 Parts FAQs
Answers on the start cartridge, shield cup, tips, electrodes and guide used on a light-duty hand plasma torch, and how to look after and choose them.
What does the start cartridge in a hand plasma torch do?
Many hand plasma torches use a contact (blowback) start. A spring-loaded part inside the torch holds the electrode against the nozzle. When gas flows, its pressure pushes the electrode back, the parts separate and a small arc forms between them, which becomes the pilot arc used to start the cut.
The start cartridge is the spring-loaded part that carries this movement, so it has to move freely. It sits between the electrode and the tip. How it is built differs between torches, so follow your manual.
How can I tell that the start cartridge needs replacing?
Because the cartridge has to move freely for the arc to start, signs of trouble are a torch that is slow or sticky to fire, an arc that sputters, or a part that feels stiff or gritty when you press it. Heat damage or debris inside it can also stop it moving.
These signs are only guidance, and other faults such as loose or wrongly fitted parts, damp air or a worn electrode can cause the same symptoms, so check those first. Fit a replacement when the cartridge is damaged or will not move freely, and follow your manual.
What does the shield cup do, and when should it be replaced?
The shield cup fits over the front of the torch and protects the other consumables from the molten metal and sparks thrown up during cutting. Slag on it can also upset the gas flow.
Check it each time you change parts. Remove any loose slag, and replace it if it is cracked, eroded, burned, has stripped threads or has gas holes you cannot clear. Check that it seats properly when refitted, because a poorly seated cup is a common reason for a torch not firing or cutting badly. Always let it cool first.
How do I check how worn an electrode is?
Switch off, let the torch cool, then remove the shield cup, tip and electrode. Look at the small insert in the electrode's end: it wears into a pit. Replace the electrode and tip if the pit is wide, uneven or rough, or has reached the depth limit your manual gives for that torch.
Makers set that limit by current rating and cut-quality needs, so do not rely on a figure from another torch. A pit gauge or a straight edge and a bright light help you judge depth. Drop in cut quality is another sign it is time to change.