DYNAMOMETERS. Alden's Absorption Dynamometer.—Mr. George I. Alden (Trans. A. S. 31. E., vol. xi) describes a new automatic absorption dynamometer, shown in Fig. 1, as follows: "This dynamometer is essentially a friction-brake, in which the pressure causing the fric tion is distributed over a comparatively large area, thus giving a low intensity of pressure between the rubbing surfaces. The pressure is produced by the ac tion of water from the city pipes. Enough water is allowed to pass through the machine to carry off the heat due to the energy absorbed.
The rubbing surfaces are finished smooth and ran in a bath of oil. A valve operated by the slight angular motion of the dynamometer va ries the supply of water, and consequently the pressure between the frictional surfaces, thus securing automatic reg ulation.
" Referring to Fig.
1, A is an iron disk keyed to the crank-shaft, The sides of this disk are finished smooth, and each side has one or more shallow radial grooves, as shown at X. The outer shell consists of two pieces of cast iron CC bolted together, but held at a fixed distance apart by an iron ring and by the edges of the copper plates EE. Each of these plates at its inner edge makes with the cast-iron shell a water-tight joint, so that between each copper plate and its cast iron shell there is a water-tight compartment, into which water from the city pipes is ad mitted at G, passes to the opposite compartment and is discharged through a small outlet. The inner chamber is filled with oil, which finds its way along the grooves in the disk A. The shaft is free to revolve in the bearings of the cast-iron shell C C. The shell has an arm carry ing weights, which has its angular motion limited by stops at P and Q. An automatic valve regulates the supply of water to the machine and is so adjusted that a slight angular motion of the brake varies the free water passage through it. The outlet aperture being small and constant, the pressure of the water in the compartments is thus automatically varied.
"The dynamometer is operated as follows: The inner chamber being filled with oil, weights are suspended from the arm to give the desired load. The engine is started, and when up to speed a valve is suitably opened in the water-pipe leading to the automatic valve, which latter, being open, allows water to pass to the outer compartments. The pressure of
this water forces the copper plates against the sides of the revolving disk A—with which they were already in contact—cansing sufficient friction to balance the weights upon the arm, which then rises. This motion operates the automatic valve, checking the flow of water to the brake and regulating the moment of the friction on the disk to the moment of the weights applied to the arm of the brake." The Richards Absorption Dynamometer, designed by Mr. C. B. Richards, consists of a tank A II (Fig. 2) within which two paddle-wheels revolve in oil, thus producing a resistance and a tendency to rotate the whole tank, which is mounted on friction-rollers. This tendency to rotate is measured by the lever-arm act ing on a platform scale. By means of a valve the oil in the tank can be allowed to circulate with greater or less free dom: by closing the valve a pressure is brought to bear on the oil in the tank, so that the resistance to the rotation of the inner wheels thus be comes a drag on the driving power ; when the maximum resist ance is obtained with out decreasing the number of revolutions per min. of the shaft, the force of resistance. meas ured on the scale-beam, will enable us to calculate the horse-power consumed. In order to prevent any change of temperature in the oil, a constant stream of water is discharged on to the tank through a perforated pipe P above it. Beneath the tank proper a metal receiver catches the water, which is then carried off by the waste-pipe IV, shown at the bottom of the receiver.
Tatham's Belt Dynamometer is shown in Fig. 3. In this ap paratus the difference in tension of the slack and driving sides of the belt is exerted to vibrate a system of lever-arms and scale beam. The belt from the shaft drives the dynamometer in the direction indicated by the arrows, a and a' being respectively the tight and loose belts, or rather sides of the belt, driving the pulleys E and F.7 on the vibrating frame B. The vibrating frame B is bal anced upon knife-edges at C. and is provided with similar knife-edges at if, which engage the links of the scale-beam. The dis tance from C to is equal to the effective diameter of the pulleys E and E' upon the vibrating frame; a pulley .5/ keyed to lower shaft communicates motion to the ma chine to be tested, the direction of belt being as shown.