ANALYTICAL CHEMISTRY
2004 in a furnace with carburizing compound a t 1900' F. for 15 to 30 minutes, quenched in oil, and tempered for 1 hour a t 400" F. All surfaces of the hardened valve stem except the threads were then ground to the final dimensions under conditions that produced a high polish. Before olishing, the stems had a hardness of 56 to 58 on the Rockwell scale.
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velopment, several other types were considered, including manual and automatic Toepler pumps, pumps in which a piston is moved by an external solenoid, diaphragm pumps, and fans rotated by external magnets. However, none of these offer all the advantages of the present pump. Operation is simple, automatic, and essentially trouble-free under conditions of either constant or varying pressure. There is no possibility of gas leakage into or out of the system through the pump. Power is transmitted by positive mechanical pressure of a cam external to the system, which makes it unnecessary to maintain moving gas seals with the sides of the closed system.
CHECK VALVE
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9 A
u
F I L L TUBE
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inches Figure 1. Valve Assembly 1. Brass nut 2. Brass wheel 3. Valve stem, 440-C stainless steel 4. Brass packing gland 5. Brass valve bonnet 6. Teflon packing rings 7. Packing bushing, 18-8 stainless steel 8. Shoulder for protective cover which slips over valve stem 9. Valve body, 18-8 stainless steel
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n /NYLON P l S T O N i
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STAINLESS STEEL
This valve is far superior to those of conventional construction in which both the valve stem and body are made from an 18-8 stainless steel. Valves made entirely of 18-8 have a tendency to score a t the needle cone, A (Figure 1) and are also more susceptible to leakage past the packing a t B. The heat-treated 440-C stainless steel valve stem, when hardened, ground, and highly polished, eliminates both of these disadvantages. The valve stem is not scored either by the valve seat or by the 18-8 stainless steel bushing (Figure 1, 7 ) used to compress the Teflon packing rings (Figure 1,6)since both of these parts are made of the much softer 18-8 stainless steel. The primary function of the bushing is to center the valve stem and permit pressure to be applied to the Teflon gasket seal. In opening and closing the valve, microgrooves in the Teflon gasket seal are avoided by the highly polished, hardened valve stem. ACKNOWLEDGMENT
The authors wish to acknowledge the assistance of F. M. Reinhardt, S. J. Rosenberg, and C. R. Johnson, of Metallurgy Division, National Bureau of Standards.
Gas Circulating Pump for Closed Systems
BOSTON GEAR RATIOMOT CAT NO MCBSWS 083H 3 4 5 RPM OUTPUT
The height of the mercury piston is maintained so that a t all times there is a positive pressure of mercury on the mercury pump. For this reason, the O-ring seal need only be mercurytight, and air cannot leak into the system through the pump, even when the system is evacuated. Pumping rates can be (-011tinuously varied from a few milliliters to approximately 0.5 liter per minute by adjusting the piston stroke. Larger pumping rates could be obtained by increasing the displacement of the mercury pump. The exhaust and intake valves were obtained from a n automobile fuel pump. Pumps of this type are now in use on a glass and a metal system. The operating pressure ranges of these systems are 3 to 20 and 15 to 115 pounds per square inch absolute, respectively.
W. H. Burke, Jr., and W. G. Meinschein, Field Research laboratories, Magnolia Petroleum Co., Dallas, Tex.
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PUMP has
been developed for circulating a mixture of reaction gases over a catalyst in a closed system in which the pressure decreases markedly as the reaction proceeds. Prior to its de-
ACKNOWLEDGMENT
The authors wish to express their appreciation to W. F. lfueller and Horace Early for their assistance in fabricating the mercury pump.
