One of the least favorite parts about repairing an ANSI pump is removing the impeller. Impellers in this style of pump screw onto the shaft, and over years of service the impellers can get screwed on awfully tightly. Unfortunately, there is no easy way to grab the impeller to remove it. All sorts of tools are used, usually a big vice grip wrench is clamped on to the edge of the impeller and either another vice grip or a channel lock is used to grip the coupling end of the shaft and the two are turned against each other. The coupling end often ends up with scrapes and the impeller can wind up bent.
Even worse, some folks get the great idea to heat up the impeller eye with a rose bud to loosen up the impeller. However, there is a gap between the end of the shaft and the impeller where fluids or vapors are present. The additional heat from a rose bud will greatly increase the pressure in this tiny cavity to the point where the middle of the impeller can get blown off. And blown off like a bullet, going right through walls (hopefully, if it misses the pump technician).
The answer to these is a specifically designed impeller wrench. Just slip it over the shaft WITH THE KEY on the coupling end (positive grip with no damage to the shaft) and slam it down on your workbench. The inertia of the impeller will keep it spinning when the shaft stops abruptly, spinning the impeller right off the shaft. In extreme cases, it may take 3-4 whacks, but I have never seen an impeller wrench defeated.
A must have for people who rebuild ANSI pumps.