This is another heat exchanger which makes use of the hot boiler furnace exhaust gasses as they head up the flue. The economiser has a bank of tubes through which the feedwater is pumped under very high pressure by the boiler water feed water. The hot gasses pass on the outside of the tubes and a soot-blower may be fitted to blow the accumulation of soot from the tubes. A disadvantage is that condensation of the flue gasses can lead to acid eroding tubes and casing, the correct choice of materials for these components is imperative i.e. stainless steel used.
5. Main Feed Water Check Valve
This is a screw-down non return valve and is fitted to the feedwater inlet pipe to the boiler, normally being full open. A wee aside to this; I was a young lad sitting part A of my Second’s Tickets in the Board of Trade Office in Belfast in the late sixties. I had got about half way through the drawing paper which was- yes a boiler check valve, when I discovered to my horror that I had chosen a wrong scale and was about to run off the paper. Just then a loud alarm sounded, everybody was evacuated to a safe area outside as there was a bomb alert in the building.
Great I thought, we will have to start over again when we get back in and this time I will get the scale right! Alas; it was a false alarm and we were back inside in ten minutes, being instructed to carry on where we left off. Needless to say I had to resit the drawing part of my tickets!
Anyway the check valve acts as an isolating valve if working on the feedwater line with furnace shutdown. Non-return or no – always shut it tight!
6. Feedwater Control Valve
This is an automatic valve situated between the economiser and the main check valve. It controls the level of water in the boiler, opening and closing as required.