Hi Bentyfield Diggers!
Had a look at my Bentyfield plans.
The Engine house plan as, I thought is more or less that.
It shows an existing engine house(presumably a chamber),more or less butting onto a new engine house, again presumably a chamber.
The two are linked by a line which is labelled high-pressure pipes! This would suggest it must be some type of water pressure engine -like Sir Francis.
The only level shown is Bentyfield Horse Level.
Now,also in my possession is a copy of a plan and section of this mine terminating at the Western boundary.
If my memory is correct I am sure that Bentyfield was worked by two different companies and this Westeren boundary would fit this.
Also on this plan is an engine sump, which clearly comes off the Bentyfield horse level.
My guess is, this the site of the engine chamber. This plan is in Cumbria record office.
Hope this helps.