Mr. Bond of the DVLR:71104 wrote:Please could you explain the function of an exhaust bypass?
It's a modification I initially made to drain excess condensate out of the motor when running, but it had other unexpected uses. When the loco is stationary if I open the forward running drain cock, put the reverser into reverse, and then open the regulator, steam is sent though the port block, and out of the drain. This heats the whole motor up. With sufficient heating the loco can be driven off without any pushing or shoving (which used to be the case). Nowadays, when the loco is standing I leave it in reverse with the drain cock open, passing a little steam to keep the motor nice and hot.
In forward gear, with the drain cock open, some of the exhaust steam is directed out of the drain. The idea of the drain cock was to relieve some of the torturous route that the exhaust has to go through to get from the lower ports up to the reversing valve and beyond.
Here is a diagram of the port block showing the drillings. The brass tubes that connect to the exhaust bypass valves are connected to the long vertical drillings that feed steam/exhaust to or from the front ports in the port block.
Here is the port block attached to mounting bracket showing piping and valves:
This loco has the exhaust directed underneath the boiler and up the flue to draw the fire. If a bypass valve is open too much not enough steam will be made, and if closed too far too much steam is made. It differs with the weather, and fine tuning can get the steam production just right.
Best wishes,
Dave.
