SummaryThe milking characteristics of 4 transparent and 8 conventional rubber teatcup liners in new condition were compared for peak flow rate, machine time and strip yield, using 30 cows in two 15×15 Latin squares. The milking characteristics of transparent liners were similar to those of normal liners at the same cluster weight. The 4 transparent liners were then compared with 4 of the conventional liners using 16 cows in two 8×8 Latin squares, to observe the movement of teats within the liners throughout milking. The various analyses indicated significant differences between liners but the ranked liner mean values showed the transparent liners widely distributed in the range. It was concluded that findings from studies of teatcup action using transparent liners could be expected to apply also to conventional liners.The conventional liners were selected to form groups differing mainly in one physical characteristic only (stiffness of the mouthpiece, wall thickness, bore and rubber hardness). Within groups, there were no significant differences in milking properties of practical importance, but between groups there were small differences in machine time and strip yield. Two properties of the liners which appeared important in controlling movement of the teat into the liner were bore of the barrel and friction, bore having the greater influence at the beginning and friction being the dominant influence at the end of milking. With the transparent liners it could be seen that the end of the teat was frequently bathed in milk. Both with transparent and with conventional liners it was surprising how often the teat penetrated so deeply that complete collapse of the liner in each pulsation cycle was prevented.

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STJMMABY. The milk flowing during a single pulsation cycle was collected in a circle of contiguous cups which rotated in a chamber at 1 rev/pulsation cycle just below the end of the teatcup liner. The mean flow rate during the time taken for each collecting cup to pass under the milk stream was calculated and the flow-rate curve for the milkflow period of the pulsation cycle plotted. Flow rates were measured at 130, 97, 65, 32 and 16 c/min, and also after the pulsator had been stopped with the liner open for 0-5 min (0 pulsation).It was concluded from the series of flow-rate curves at the different pulsation rates that flow rate from the teat increased in about 0-05 sec to a steady value which continued for 0-5 sec or so, and then declined over a period of about 1-5 sec to a new constant value approximately equal to that shown after milk had flowed continuously from the teat for 0-5 min.These results suggest that once the pressure difference across the streak canal during milking forces the teat sphincter open a considerable time elapses before the muscle control system responds, and that a further much longer period elapses before the full closing force of the sphincter is exerted. Thus, it would appear that at pulsation rates of about 50 c/min and above, the streak canal is closed by pressure exerted on the teat by the closing liner, the sphincter muscle playing no active part because its response rate is slow compared with the pulsation rate. At lower pulsation rates the flow rate declines during each cycle because the sphincter muscle has time to exert a closing force to a greater or lesser extent depending on the duration of the milkflow period. Clough & Dodd (1956) and Clough (1963) showed that maximum flow during milking increased with increasing pulsation rate, and suggested as a likely explanation that flow rate within each pulsation cycle rises rapidly to a peak value and thereafter declines. Thus, with a constant pulsation ratio, the quantity of milk flowing in a period of time consisting of short pulsation cycles would be greater than the quantity flowing in the same time with fewer but correspondingly longer cycles. In the present work a simple mechanical device has been used to investigate further the pattern of flow rate from the teat within a single pulsation cycle at a variety of pulsation rates during maximum flow of milking, and a constant pulsation ratio of 50 % (teatcup liner

A method is described of measuring pressures in a teatcup assembly using strain gauge transducers and simultaneously following movement of the liner wall by means of a cine camera. In preliminary experiments with a narrow bore type liner it was found that pressures below the teat could vary during a single pulsation cycle from a few inches of mercury below atmospheric pressure (inHg vacuum) to as high as 25 inHg vacuum in the absence of an airbleed. Bleeding air into the barrel of the liner or into the clawpiece considerably reduced fluctuation in pressure, and the vacuum barely rose above the nominal milking vacuum of 15 inHg. Reducing the rate of change of pressure in the pulsation chamber did not greatly affect the maximum vacuum obtained. Opening and closing of the liner by pressure change in the pulsation chamber was under some conditions considerably delayed by the pressure conditions existing inside the liner.It is suggested that inertia effects of milk in the cluster and the natural frequency of the system are largely responsible for the observed pressure changes under the teat.C. C. THIEL, P. A. CLOTJGH AND D. N. AKAM METHODS Pressure measurementApparatus. Bell & Howell unbonded strain gauge pressure transducers (Type 4-326, range 0-25 lb/in 2 absolute) were used in conjunction with their Type 5-124 ultraviolet light oscillograph equipped with Type 7-342 galvanometers having a flat (within 5 %) frequency response range of 0-135 c/sec to a sine wave input (Bell & Howell Ltd., Consolidated Electrodynamics, 14 Commercial Road, Woking, Surrey). With this combination of transducers and galvanometers no amplifiers were required. Each transducer was connected to a galvanometer through a resistance network so that the output of the bridge circuit could be adjusted to zero when the transducer was subject to prevailing atmospheric pressure. Also a variable resistance was fitted in the input circuit of each transducer so that the deflexion of the galvanometer for a known pressure change could be matched to the grid lines on the chart. A convenient chart speed was 3-25 in/sec with timing lines at intervals of 0-1 sec.The transducers, being somewhat bulky and weighing 4 oz, could not be conveniently mounted direct on the teatcup assembly. They were therefore mounted 1-5-2 ft away from the clawpiece along the line of the long milk tube. Short pieces of 0-125-in. bore thin-walled stainless steel tubing, ending inside the liner at the positions selected for pressure measurement were sealed through the base of the liner and shell so as not to interfere with the milk outlet. These pressure probes were connected to the transducers by high density polythene tubes 0-110 in. internal diam.x 0-161 in. external diam. (Portland Plastics Ltd., Bassett House, Hythe, Kent). The inlet pressure cavity of each transducer and its connecting tube and pressure probe were filled with liquid. This was to maintain the frequency response of the system and to reduce inertia effects that would inevitably have occurred when a nominally air-fil...

Milk is obtained from the teat during machine milking by the creation of a partial vacuum; the rate of flow is influenced by many factors including changes in the vacuum, the pulsation rate or ratio, alterations in the design or construction of the teat cup liner. Recent research relating to these problems has been reviewed by Dodd & Clough(i).The rate of milk flow or machine milking rate is usually expressed as the mean rate of flow from one or more teats over a specified period of milking. In this way it is possible to show whether a change in the milking machine affects milk flow but not how the change is brought about; for example, it is possible to demonstrate that an increase in pulsation rate and teat liner tension causes much faster milking but the reason remains obscure. In order to discover why such changes in milking rate occur it is necessary to measure the proportion of time during which milk flows in each pulsation cycle and the rate of flow of milk during the flow period. In this investigation we have studied some aspects of this problem with the aid of a portable X-ray cine-camera (2). METHODThree cows accustomed to machine milking were milked in a two-level stall designed so that the movement of the cow could be restricted. The left front teat of each cow was turned up against the udder and held in that position with adhesive tape to allow an unrestricted view of the right front teat. The right front quarter was then milked until most of the milk was removed. The teat cup assembly was then removed from the teat and a warm (100° F.) sterile suspension of barium sulphate (Micropaque: Messrs Damancy) was infused into the udder through the teat orifice with an enema syringe. The aim was to achieve a 25 % suspension of barium sulphate in the udder contents so that there was sufficient opacity for the cineradiography.The teat cup assembly consisted of a normal extruded teat cup liner (Alfa Laval 20003 B) fitted into a glass teat cup of standard size. When a liner is caused to pulsate the collapse is always in the same plane: in this experiment the liner was applied to the teat so that the plane of the collapse was parallel to the X-ray beam. The milking machine vacuum under different conditions was measured with a mercury manometer, the pulsation ratios had been previously determined by a cine-camera technique (3), and changes in liner tensions were measured with a spring balance (4). The X-ray camera was operated at 50 frames/sec.: the exposure time for each frame was T^5 sec.