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THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
the valve stem in place. Four 8/1&. holes are cut in the side through which the gas escapes into the outer shell. The electromagnet (7), which is attached to the upper plug as indicated, is made from a piece of soft iron and is 33/4 in. in length and l s / 4 in. in diameter, and has a wall thickness of in. A brass washer screwed into the bottom of this soft iron shell is drilled and tapped with a 3/4-in. hole into which is fitted a soft iron spindle (7). This spindle is wound with No. 24 copper wire, one end of the wire being attached to the spindle while the other end passes out through the stem (6). Rod (6) is drilled with a 6/32-in. hole, through which the insulated lead from the electromagnet passes. The upper end of this wire is passed through a soapstone cone, squeezed into the upper end of rod (6) by means of a compression nut and washer (11 and 13). Rod (6) is fastened securely to the electromagnet, and, by means of a handle attached to its upper portion, the electromagnet can be screwed up or down. The rod is made gastight by means of a stuffing box (12). Since the valve is expected to deliver gas at 1495 lbs., and since the maximum pressure of the gas storage may reach 3000 lbs., it is evident that the valve spring must be adjusted so that there is practically no leakage on a 1500-lb. differential. The spring is therefore adjusted before the valve is assembled by applying 1500 lbs. pressure and screwing the adjustable guide (4) down until the valve stem holds. The valve and electromagnet are screwed into the supporting shell as indicated, the assembly being made gastight by means of annealed-copper FIQ.6 ring washers (5). For this particular vaGe it was found that the magnet could be screwed down so close to its armature that satisfactory operation was obtained with 0.5 amp. at 15 volts. The conventional relay connections to the regulating gage are now made and the valve is ready for operation. In Fig. 4 are reproduced recorder charts showing the operation of the valve for four successive days. A third point requiring close regulation lies between the low-pressure flowmeters and the ammonia decomposers or scrubbers. In order to make the flowmeter readings comparable, it is necessary to maintain a constant back pressure, 50 cm. of mercury being selected as best meeting the needs at this particular point. This low pressure makes possible the use of a mercury manometer for opening and closing the relay circuit which operates the control valve. In the case of the high-pressure valve described above, it was desirable that the valve remain closed in the event of a failure on the part of the electrical system. For regulating the back pressure on the flowmeters, however, the valve ought to remain open, so that if the control fails to operate no excessive back pressure will develop. Instead of arranging the magnet so that it lifts the valve stem, as in the case of the high-pressure valve just described, a valve was constructed in which the valve stem was pulled down onto its seat by the magnet. Fig. 5 makes the constructionhl details of this valve sufficiently obvious so that no further description seems necessary. Although these valves have been designed to meet the special requirements of an ammonia-catalyst testing plant, it is believed that the principle involved can be readily applied in the solution of other problems where close regulation of gas or liquid flow is essential.
Vol. 14, No. 11
The Plastometer as an Instrument for Process Control By Eugene C. Bingham, Herbert D. Bruce, and Martin 0. Wolbach, Jr. LAFAYBTTE COLLEGE, EASTON, PA.
N THE control of processes involving the use of amorphous materials, we often desire something more than a chemical analysis. For example, the analysis of rubber, nitrocellulose, or clay leaves much to be desired, and so physical methods are resorted to. But these methods have proved difficult to handle, owing to the lack of definitive character with this class of substances. Amorphous materials lack a true melting temperature, but, nevertheless, in our need of something definite we try to measure the softening temperature of a bitumen. Colloids do not form true saturated solutions, and therefore the attempt to measure the solubility of, say, nitrocellulose in acetone does not appear promising. It was thought that the viscosity might be definite, but that too appears to be indefinite and to depend entirely on the conditions of the experiment. At first this difficulty only seemed to occur at the higher concentrations of the disperse phase, where the material was said to be plastic. Now we find that all colloidal solutions appear to share this difficulty. A paint supposed to be viscous showed a change of 10 per cent in the viscosity when the shearing stress was scarcely trebled.
I
I30
2.4
120
2.2
110
2.0
too
Weight Percentage Lithopone FIG.I
The variable-pressure viscometer and plastometer promise to do much in removing these difficulties. With a given material a definite shearing stress, known as the yield value or friction, is required to start the flow. The amount of shearing stress required in excess of this to produce a given flow is a measure of the mobility. Since all matter will flow under appropriate conditions, these properties (together with fluidity) are of wide applicability. Moreover, in many cases the flow properties are of direct interest and importance -as in paint, glue, clay, rubber, plastics, etc.
