The flowmeter, top left, manufactured by George Kent, measures and records the water output from the pump into the service main. As the water enters the service main, it passes through a restriction called a Venturi. The pressure differential developed across the Venturi is proportional to the flow rate.
The W.R. Combustion or CO2 Indicator, top right, manufactured by International Gas Detectors, Leeds was installed in the boiler house and was used to record the level of carbon dioxide (CO2) in the flue gas. The CO2 level was an indicator of combustion efficiency. Getting it right ensured the most economical use of the coal. A continuous sample of flue gas was brought to the instrument in copper tubes where it was filtered then passed through the large copper vessel in which it was exposed to Soda Lime where the CO2 content was absorbed creating a reduction in pressure compared to the incoming gas. The more CO2, the greater the difference.The differential pressure acted on the bellows and moved the pen across the chart which rotated once a week driven by clockwork leaving a permanent record of combustion efficiency.
The two lower photos are before and after photos of a pressure gauge panel. When the engine house was taken out of service in 1980, the basement flooded and these gauge were underwater for nearly 15 years. Surprisingly, the mechanism was still in very good condition so with the exception of dial plates and pointers which had to be remade, the gauges were restored to working condition.