Fan replacement and duct adaptation

01

The fan comes to site as one assembly — casing, impeller, motor and base frame together. What decides the job is not the fan itself but its connection dimensions: the inlet, the outlet and the bolt pattern under the frame. On a replacement they rarely match what is already there, and here they did not.

02

The fan is landed on its base and stays on the sling until it is fixed down. The old frame did not leave the seats where the new one needs them, so they are made to suit the new footprint before anything is bolted — a fan sitting on a base that is out carries that error straight into its bearings. Anything hot happens over a blanket, with an extinguisher at the work front.

03

The inlet side is where the old ducting has to give. We take the weight of the duct on a sling first, so nothing is hanging on the joint once it is open, then cut it back and set a stub into it to suit the fan inlet. The fan drawing gives the size; where the stub lands is measured on the duct itself.

04

The outlet goes up into the existing stack, and the two do not meet on their own. We make the transition, offer it up with the fan standing on its base, and mark it in position. Nothing is finish-welded until both ends have been proved against the openings they have to land on.

05

Both connections finish on something flexible — a sleeve at the inlet and a bolted expansion joint at the outlet. The frame itself stands on anti-vibration mounts, so the machine is free to move a little; these two joints are what keep that movement out of the ducting, and they let the flanges sit a fraction out of line without loading either side. With those in, the adapter welds are dressed back and the expansion joint is bolted up all round.