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Water Mill Speed Indicator

Line shaft speed indicators were used to monitor the speed of grinding in grain mills as well as in other applications. A flyball mechanism inside the metal housing operates a rack working on a pinion gear on the indicator shaft. The two counterweights at the ends of the needle limit its movement. The mill operator manually opened or closed the gate, controlling the water flow to keep the needle at the specified reading. In this case, the midpoint of 300 rpm was desired. The 6” wooden pulley on top of the device would be belted to the lineshaft and directly drives a flyball apparatus. The front of the indicator is 15 1/2” wide by 14” high. The 15” long body, including a 13” long metal cylinder, can be wall mounted, the backboard having 6 holes for this purpose. A sliding door on the side of the metal cylinder reveals the flyball mechanism, identical to that in early steam engine governors.

A paper label on the sliding door reads:

DIRECTIONS - The indicator should be located so as to be conspicuous from the mill floor generally. If run in connection with water power, so as to be seen from the gate wheel.


If the shaft to which the indicator is connected is weak, it should be belted as near the bearing as possible. See that the bearing is tight so as to avoid all “trembling”.

When a driving pulley is necessary, it should be “trued off” after being secured to the shaft, as every vibration of the shaft or irregularity of the pulley will be communicated to the pointer. Use a soft smooth belt with a smooth splice 7/8 of an inch wide, (good harness leather of uniform thickness is best).

The arms of the alarm, which the balls strike, may be bent up or down so as to strike at any speed desired. If desireable, when shutting down, or at any time the motion cannot be kept up, the hammer may be hooked back.

Oil the inside bearings with good sperm oil once in twenty four hours. The top (bearing) never needs oiling. The alarm wires (should) be oiled occasionally.

The indicator is complete and working. Hoiwever, the innstructions mention an alarm device which the balls would strike as they moved outward sufficiently. There is a small iron fitting on the inside of the back board which probably retained this striker wire. Hearing such an alarm would likely be difficult, even in a water powered mill, which may account for its absence.

The metal has original red paint with gold striping, still in fairly good condition. The glass is missing from the face. It was held in with conventional triangular glazing points, still present.

front view

large wooden pulley

flyball mechanism

left side

Directions label

Price: sold
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