Our working boiler is a 1910 Galloway boiler installed at the same time as the Pollit and Wigzell engine. This is a prime example with plain furnace tubes. We also have a secondary boiler in preservation.
In each of the two furnace tubes is a grate that extends six feet back to a brick wall with a gap at the top to allow the hot gasses to be drawn along the tube to the back of the boiler. At the far end of the boiler there is a brickwork chamber which directs the gasses down to a flue which brings them under the middle of the boiler to the front behind the brown glazed brick wall. At this point the gasses are split and sent down a flue at either side of the boiler shell to the dampers and the outside flue down to the chimney. This “three pass” system of flues ensures that the majority of the boiler surface area is exposed to the heat generated by the fires thus increasing efficiency.
The large weights suspended on wire ropes at the front of the boiler counterbalance the large plate dampers at the far ends of the side flues. These are raised and lowered to control the rate of combustion of the two fires. The most important factor in boiler management is knowing and controlling the water level within the vessel. In the two vertical brass gauge frames on the front plate there are thick glass tubes which show the operator the current water level. The pressure gauge at the top of the front plate indicates the steam pressure within the boiler.
Behind the pressure gauge on the top of the vessel is the deadweight safety valve which releases excess steam to prevent damage to the boiler and the resulting danger.
The crown valve isolates the boiler from the steam pipework supplying the engines and pumps on the site. Further along the boiler is the water level alarm which is a float operated device that automatically gives warning of too high or too low water level and also acts as a second pressure safety valve. The large round manhole provides access to the inside of the boiler from the top. You will notice a smaller oval access manhole at the bottom of the front plate of the boiler as well.