I was interested to see that Jason Kovac of The Train Department in New Jersey, USA, offers a precision made replacement gas valve for use in Accucraft locos. My Accucraft GVT tram loco runs reasonably well, but the gas control could be better, so I decided two order two replacement valves, one with a built in handle, for Dora, and another without handle for the GVT loco, which already has a nice handle on the gas control valve.
The replacement valves arrived from the USA in around a week from ordering. The original valve is in one piece, with a single 'O' ring providing a gas seal: the replacement unit is in two pieces, comprising an outer sleeve, which screws in, in place of the original, and a finer inner control valve with two sealing 'O' rings, which screws into the outer sleeve.
In order to provide a good seal, the thread on the outer sleeve needs to be sealed with either a small amount of thread sealant or some PTFE tape. Despite the fact that I have some PTFE tape somewhere, I ordered some thread sealant to arrive along with the valves.
Fitting the replacement valve to Dora was straightforward, once the loco body was removed to improve access. The loco now steams more easily and the gas is very controllable, the flame is still a bit erratic, so I may also try a replacement precision gas jet (from Chuffed 2 Bits) but the loco runs fairly well now.
I didn't have much success with the GVT loco, after fitting the replacement valve, the control became very stiff to operate, but the gas could not be shut off. I took the new valve out and tried the old one - same problem. I finally diagnosed that some thread sealant had attached itself to the valve seat and then hardened, making a tight seal impossible. I withdrew the valve again and used a 5mm drill bit, held in my hand to gently clean the valve seat. I re-fitted the original valve, and all seems to be well. I haven't put the replacement back yet, I think I will use PTFE tape as a sealant this time!