When steam is exhausted from the low pressure cylinder, it is recycled as efficiently as possible. The steam passes through a surface condenser which condenses the steam into water producing a vacuum, which acts on the low pressure piston, supplementing the thrust from the high pressure exhaust steam acting on the other side of the piston.
The condenser is located in the impound chamber beneath the engine house floor and is submerged in water from the boreholes, which is used to cool the steam within the condenser tubes. To ensure that it remains covered at all times the borehole pumps were designed with a slightly greater pumping capacity than the ram pumps. The impound chamber was therefore always full with the small overflow being piped back to the bore hole.