More of the Cover-Up

Question: What are these four for?

Portly Swans Greeting? Not really.

Although I didn't draw attention to them in my previous article, there are four access holes in Sentinel 7109's boiler top cover. The holes need to be covered when not being used and that is what the above four items are for. The cut-away allows each access hole to be opened without removing the fastening nuts.

Top Cover access holes (the other half is similar to this)

The four holes in the twin top covers are situated above four corresponding plugged holes in the boiler top plate.

Plugged holes in the Boiler Top Plate

Some more detail is shown in this drawing below.

Plan view of boiler top plate with plugs shown in red

The plugs are able to be removed for access to the superheater and boiler tubes below it.

Access plug removed

By opening an access hole in the top cover, a box or socket spanner can reach into the corresponding top plate plug. A steam lance, pressure washer wand or compressed air nozzle can then be inserted to blast away soot and 'detritus' from the superheater and boiler tubes.

Later Sentinel locos such as 9622, changed the plugs for nozzles with a steam supply connected to them directly. In this way, the superheater and tubes could be cleaned simply by turning on a steam supply valve. Currently there is no plan to put this on to 7109 although it's very tempting!