For beating some papermaking fibres, a Hollander beater is essential. One of the brands preferred by hand papermakers is the Valley Beater, originally made by Valley Iron Works, but still available new from Voith-Sulzer (last time I checked). They are generally available used for 2 or 3 thousand dollars, but new ones are over $10,000. They were originally designed for use in the laboratories of commercial paper mills for testing pulp and determining how the main batch should be processed in the large production equipment. Because they were intended as a lab instrument they can essentially be kept running forever, although parts are becoming more expensive as well.
Most of these beaters have a painted cast iron tub, but ours has a bronze tub and the naked metal to show it off. We have it on casters so we can roll it out of the way when not needed.
Because the water supply lines go up to the tabletop, the area around the diaphragm cannot easily be emptied. I eventually plan to run the water line down into the box that already contains the motor switch and have the hose connection there. In this way one can disconnect the hose and drain the beater a little more fully. I will also add a short hose with a sprayer to help with rinsing out the beater tank when the time comes to clean up.