Throttle Valve

[318J]

Hi all.

I'm replacing the throttle valve on a locomotive, the valve lives inside the smokebox so it needs to be able to withstand high temperatures. (1/2" valve and also needs to be rated for at least 150psi of steam).

Does anyone here have an idea what sort of temperature the inside of a smokebox can reach, and thus what temp. rating I should aim for with the valve? Looking at preferably getting a stainless valve for the environment it's in.

And ideas of recommendations? Thanks.

[Fender]

I used this SS valve in my smokebox, and so far it has held up. It uses a graphite-composition seat.

[ChuckHackett-844]

I had a friend with a coal burner who melted the Teflon out of a brass ball valve throttle in the smokebox. All we had available to get him running again was another of the same valves. We wrapped that one with fiberglass insulating 'caulking' tape (used on wood stove vents) and he was fine. Mine (brass butterfly valve) is also wrapped with the same tape in the smokebox but I burn propane.

[Dick_Morris]

Do a search. Several years ago there was a thread with comparisons of temperatures of the outside surface of the smoke boxes of several locomotives.

There was also a recent post giving a source for a ball valve that gave a progressive opening.

[Fender]

There can be a huge difference in smokebox temperature depending on the location. If measured directly in front of the tubes/flues, the temp will be higher than it would be against the top of the front tube sheet. But this location is difficult to access for repairs or maintenance. I agree that insulating the valve is beneficial. Inside the smokebox, the steam flowing through the valve is probably “cooling” the valve. At 125psi, saturated steam is about 350F, which is likely less than the temp inside the smokebox.

[318J]

I went ahead and got a ball valve rated for 600°F at 900psi of steam pressure. Insulating the valve is standard practice for me, hopefully it will last long enough to get my monies' worth out of it.

As things always go, it's not a matter of *if* but *when* it will need replaced. Inevitably if the temperature doesn't get it the constant open, shut, and throttling will wear the valve out. I know a ball valve isn't perfect as a throttle, but it works and the ease of availability and price point gives it an edge.