Engine Testing

I discovered a simple answer to a question that won't occur to many Sentinel owners: On a double-engined loco such as 7109, how to you test one of the pair of engines without the other one loading it?

I was surprised but relieved to find that I wasn't the only one to have thought about this and that a vital feature had been already included by Sentinel in 7109's design.

In order to use one engine only, the steam to the other needs to be isolated. However this is not sufficient as air has to be allowed in instead to prevent the isolated engine from drawing a vacuum when the valve timing dictates that steam should be entering its cylinders.

This is how it works.

White insulated main steam feed pipe

The main steam feed pipe, from the boiler at the rear to the engines at the front, runs underneath the central water tank. It then splits into two smaller pipes, one to each engine, using a 'Y' splitter. The 'Y' splitter component makes it easier to insert a blanking plate in one or other engine's steam supply.

'Y' splitter highlighted bottom right
(Click the picture to enlarge it)

The vital feature I mentioned above is a bolt head which can be removed to open an air vent.

Vital feature highlighted to the left

Thus, by putting a blanking plate in the steam feed at the 'Y' splitter and removing the respective vent bolt, one engine can be disabled without loading with the other.