This is meant as a guide. The site takes no responsibility for the info contained, you use it at your own risk. Some basic safety before working on the rifle. 1) Make sure there is no pellet in the breech 2) Engage the test (T) mode 3) Remove the cylinder Removing the regulator and knock open valve. When removing the cylinder, as well as a small release of air from the cylinder itself it's not uncommon to hear some air escape the reg itself, either slowly or fast or not at all. Some regs shut off with a little click, some don't and some don't make any noise. If you're not comfortable with removing the action from the stock, then this is probably not for you. But assuming you have then you should have something like this. This shows a Mk2 reg (shorter, more silver in colour, with rings, as opposed to the older Mk1 regs which are more golden and lack the rings and are longer). Before undoing the 2 bolts marked with the arrow, understand that the reg will still be under some pressure with any residual air contained in it, and also that the knock open valve spring also creates some pressure, so undo the bolts slowly with a 4mm allen key equally keeping in mind that the reg will want to leave the action. It's not going to fly across the room, but all the same it won't just sit there. Also, if you haven't left the rifle on test mode, and have cocked it, then releasing the trigger will impart the hammer into the knock open valve with some considerable force, and it will send both the valve stem and spring out (once the reg is removed), possibly sending them under the nearest sofa, but possibly into an eye. Take care not to ensure this will happen. You should now see something like this. The spring you see may have stayed inside the reg, not unusual. If it hasn't simply pull it off. And you'll have something like this. The valve stem can be simply pulled out. It shouldn't need more than fingers. I avoid using metal tools on parts unless I have too. Although the stem is hard steel, it just saves burrs etc. You should now have this. This shows a black valve seat in place. The arrow marks where to put a pin or pick to remove it. If you use the inner or outer edge then you risk marking the alloy block itself. Not a major deal, but all the same, there's no need. There are 4 types of seal I've come across. 3 of them are here below. The bottom green one is the problematic soft seal originally fitted by Walther to early Dominators, typically those with a Mk1 reg. It's too soft and deforms with time and temperature leading to velocity fluctuations. Junk it. The black one is the one I found in this Walther. I'm not sure if it's aftermarket or an original item. It feels like Delrin or something similar. The top one is one of Nick (Zenith Rifles) Murphy's. I've been using these for some time and they are temp stable and don't seem to deform over time. So i'll be replacing the black one (which i've damaged as I removed it) with Nick's. Walther also do a white (PTFE I think) seal, which was deemed by tuners to be still too soft. So perhaps the black one is aftermarket or it's a new mk3 seal from Walther. Who knows? Because removing the seal tends to damage them, I don't do this unless it's not a type of my liking or it's deformed/damaged. So the action will now look like this with the seat/seal removed. As you have the reg off, you can always satisfy any concerns by getting someone with a reg checker to check it over. Each tuner has their ideas on how to do this and what they should be set at. Mk1's regs are deemed to be the unreliable ones, and harder to work on. Mk2's seem ok even straight from the crate, but tuner's opinions may vary. Reassembly is pretty much a reverse of the above. You should take care to tighten the reg bolts down equally. They don't need to be tight to the point of snapping, but they do need to seal the reg to the body and take 85 bar. Tuners have suggested that there might sometimes be a gap between the reg and body due to a thicker seal being used. Also that sometimes the reg can be moved downwards so there is a gap between the the reg's upper surface and the part of the action the barrel sits in, which may aid in reducing POI shift due to it being tightened down in an i'll fitting stock. Some people polish bits, some don't. What I would say is that you want to make sure all is oil free and clean when reassembled. Below is a pic of the different types of valve stem I've come across The conical V shaped stem seems to accompany the green seal and mk1 regs. There's debate as to if keeping this but just changing the seal cures the seal's issue, or if it needs replacing with the later flat type stem (right). The two also allegedly use a different spring. I can't tell the difference, the earlier springs seem to be of a different colour, but I don't have the tools to measure the spring rate. I play safe and just fit a flat valve, new spring and one of Nick's seals, and that seems to cure the problems that i've found with other seals. The parts are cheap so you may want to order a few spares should you want to change them. If anyone has any comments/feedback or spots an error, point it out below and we'll move on. I'll do the hammer next.