Saturday, 19 November 2011

Chuffing Nozzles - Now there's a thing or four!

To turbo-charge Sentinel 7109's fire, exhaust steam is blasted up the chimneys to pull a draft of air through the coals in the firegrate. When stationary, steam is also directed up the chimneys using the blower for the same purpose. So how is this done?

Exhaust steam from the cylinders is pushed through a narrow aperture via a set of four nozzles, two in the base of each of the two chimneys.

The Four Nozzles
The nozzles sit in the base of each chimney
where the end of each of the curved exhaust pipes enters
When the nozzles were originally extracted, they were not in an operable state. There was a good amount of hardened coal-tar in the nozzle pathway and the blower rings were clogged-up so badly that only one or perhaps two holes could actually do any blowing.
Two nozzles as found after dismantling
Sentinel 7109 has its blower fed from the main superheated steam supply which contains cylinder oil. As a result, the blower has cylinder oil blown through its tiny holes; I can understand why the pathway and holes get blocked. I wonder if later Sentinels used wet steam for the blower?
The clogged blower passageway
Let's see how a nozzle is constructed:
The exhaust steam connects to the main nozzle inlet (the big hole in the flange in the picture below).
Main Nozzle casting
It then has to go through the narrower nozzle exit aperture and up the chimney.
Nozzle Exit Aperture
The exit aperture holds down a blower ring with four holes in it over a pathway to allow blower steam to be blown through the four holes.
Blower ring
Blower steam pathway with inlet showing
A separate steam supply connects to a narrower blower inlet pipe to the pathway.
Blower Inlet Pipe
It looks like this when all is assembled.
A complete nozzle assembly
And there are four of them in a double-engined loco.
The Four Nozzles again

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