Hi everyone. What are the advantages to having piston valves on a steamer instead of slide valves? Since later locos were built with piston valves, and many older engines were retrofitted with them, there must be added performance, less maintenance, more efficiency, or something. Also, can someone explain the workings of the Franklin poppet valves introduced toward the end of steam? Were they better? Thanks. Seth

The Wilmington & Western RR
sethajackson@hotmail.com

> Hi everyone. What are the advantages to
> having piston valves on a steamer instead of
> slide valves? Since later locos were built
> with piston valves, and many older engines
> were retrofitted with them, there must be
> added performance, less maintenance, more
> efficiency, or something. Also, can someone
> explain the workings of the Franklin poppet
> valves introduced toward the end of steam?
> Were they better? Thanks. Seth

"Piston" as in "poppet" or "spool"? I've always heard that slide valves had a tendency to warp when used with superheated steam.

> Hi everyone. What are the advantages to
> having piston valves on a steamer instead of
> slide valves? Since later locos were built
> with piston valves, and many older engines
> were retrofitted with them, there must be
> added performance, less maintenance, more
> efficiency, or something. Also, can someone
> explain the workings of the Franklin poppet
> valves introduced toward the end of steam?
> Were they better? Thanks. Seth

Slide valves had a problem in that in spite of
efforts to "Balance" them, the higher the steam pressure, the more they pressed down on the seat.
This not only caused extra wear on the slide and
seat, it threw considerable strain on the valve mechanism. Sometimes with disastrous results.
In the search for more power steam pressures were increased. More pressure means higher temps which
made the lube oil less efective right at a time higher pressure was putting more load on the valve seats.
The piston valve, on the other hand is self balancing and is easier to make steam tight
since the valve rings work just like the rings on an automobile engines pistons.Also, as someone posted, the inside admission left the valve chamber heads subject to the lower steam pressure of the exhaust.
The Franklin and other "Poppet" valve systems had
valves similar to the valves in a gasoline engine.
I am not familiar with how successful they were but I do remember one New York Central engine with the Poppet valves that left the IC Chicago station every day while we were at work.
It had a very distinctive and very sharp exhaust.
Trains leaving that station had to climb a ramp to go over the suburban service tracks. A pretty
good pull if you had a very heavy train. The engineers liked to start with fairly low water so the engine would steam good without carryover. The
NYC engines had a low water alarm whistle and it
was usally sounding when they were ready to start up the grade. I have never figured out how they
could bring the water up quick enough to keep the crown sheet covered when they tipped over the other side of the grade.


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