Garden Railway Forum

Sorry if this is a simple one, but my Mamod feet have only just landed - so I bought a modifed Mamod , and I've been overhauling and learning what makes it tick. One bit that has me confused is the on the smokebox , the clockhands has been replaced with what appears to be a 'valve' of some description. The 'steam out ' pipe from the reverser is routed through the chassis to this valve which appears to 'choke off' the steam through it before exhausting it to the chimney. Its a rotary type where a hole in a rod is rotated to give a shut off of not.. It seems to make no difference , exept the output noise is more of a shhhhh....shhhhh... Its that its only purpose in life.
Sorry if its obvious but I'm only just learning Mamods!

The valve is an exhaust regulator. It works in a similar way to the regulator in the cab but has one major advantage. It controls the speed in a similar way to a govenor. As the loco speeds up more steam passes through the cylinders. When the valve is partialy closed this creates back pressure in the cylinders slowing the loco. When the speed decreases, in a curve or climbing hills, the back pressure decreases alowing the loco to pick up speed again. For this to work the cab regulator is normally left fully open and the speed controlled with the exhaust regulator. It has been used on many locos but is an unusual addition to a Mamod

DLRdan:102680 wrote:The valve is an exhaust regulator. It works in a similar way to the regulator in the cab but has one major advantage. It controls the speed in a similar way to a govenor. As the loco speeds up more steam passes through the cylinders. When the valve is partialy closed this creates back pressure in the cylinders slowing the loco. When the speed decreases, in a curve or climbing hills, the back pressure decreases alowing the loco to pick up speed again. For this to work the cab regulator is normally left fully open and the speed controlled with the exhaust regulator. It has been used on many locos but is an unusual addition to a Mamod

Thanks. That also helped me get my head around it. A precise and neatly argued description of a technical Innovation.

Thanks for that explanation - thats a good and easy to understand explanation- very interesting as I have never come across one before... Brilliant and thanks again..

The exhaust regulator performs the valuable service of keeping a Mamod on the rails and below Mach 1!

Peter in AZ