06/10/2026
Before anybody asks let me qualify a few things about balancing multiple impellers or indeed any impellers. Firstly the tape round the outside is to reduce the load. I hope everyone knows you should never run an organ blower with a free/ open exhaust. Doing this is effectively making it do it’s absolute maximum work and with radially bladed impellers will definitely overload the motor. Most multistage blowers are four horsepower and upwards but this power is only up to a given flow rate and pressure. The flow needs to be restrained to a certain level. Now my balancing machine is a soft bearing machine which means the shaft supports are free to move in a single plain horizontally. This movement corresponds to the eccentricity of the centre of gravity of the impeller being balanced and hence the vibration caused by the centre of gravity not coinciding with the axis of rotation. Hope you’re with me so far!! 😀 Soft bearing machines have to balance impellers or indeed any rotating item at full running speed soooooo if the impellers were open to air flow they would draw much more than the rated power of the drive. The tape stops air flow through the impeller(s) so the load is greatly reduced and it’s possible to balance five impellers on a single shaft with just 4 HP! Hope that clears that up!
Ideally with a shaft, possibly close coupled to a motor with multiple impellers along its length, every item on that shaft rotating with it should be in balance at the running speed of the motor. With multistages this might mean five fifteen kilo impellers plus the ten kilo shaft plus an extra couple of kilos of coupling hub all in balance at 1440 rpm. If the shaft is long it is possible to put everything on all at once and balance out any vibrations at the bearing planes just by putting corrections on the outside two impellers. The problem with this is that the central impeller might be alarmingly out of balance on its own and this can cause problems because the force it generates can be enough to cause the shaft to flex or go into resonance at a slower speed. That familiar rumble that can take place as a blower is starting or stopping can be caused by just such a resonant frequency being reached. This is why I do build up balancing where components are added sequentially and at each stage a rebalance is performed. Time consuming but I think worth it!
