Check Valve - The most
common check valve in use on steam tractors are known as swing checks,
and the most common location is between the boiler and a feedwater
device. They have a hinged valve that is free to swing away from
the seat when the flow is from the seat side, but swings shut tight
against the seat when the flow reverses (this makes it the plumbing
equivalent of a diode, for those of you who are into electronics).
A misaligned or warped seat, foreign matter, and scoring can cause
the valve to leak, allowing hot water and steam to flow back into
the injectors and pumps, but on the whole they tend to be fairly
Most good check valves are built so that
they can be reground as needed, and some are built so that the valve
spins slightly with each cycle, preventing asymmetrical wear. Some
of the cheaper check valves are built with one-piece swings, and
are not able to be resurfaced - these should be avoided.