Stopcocks oblique

Fig. 1. All dimensions in centimeters, (a) 2-cm-thick glass wool plugs (b) IrCl3 on silica gel (c) Pyrex jacket for thermocouple (d) 24/40 J joint (e) Kontes 24/25 Teflon adapter with O-ring seals (f) thermocouple leads to indicating controller (g) outlet to H2S04 bubbler by way of trap (h) 2-mrri double oblique Teflon stopcock (i) N2 inlet (/ ) CO or Cl2 inlet.

Fig. 8.7. Hollow-plug vacuum stopcocks. The hollow plug is firmly seated in types (a), (6), and (c) as long as the lower section is at reduced pressure. Stopcock (d) has a hollow plug with an oblique tube in the center when the plug is turned by 180°, the lower section may be evacuated. Subsequently, only occasional evacuation of the vacuum cup is necessary. Type (e) does not have provision for evacuation of the plug and is therefore more liable to leak. Prolonged exposure of any of these stopcocks to solvent vapors erodes the grease and introduces teaks. (Adapted from Catalog C-64, Eck and Krebs Co., Long Island City, NY 11101.)...

Fig. 4. (V), to vacuum, ( Si—4)9 2- to 4-mm. oblique-bore high-vacuum stopcocks (N), inlet for nitrogen gas (T), removable trap (R), reflux condenser (L), liquid-addition tube (F), reaction flask (M), open-end manometer (U), U-tube trap.

A double oblique-bore stopcock is now joined to the jacket side tube by one of the adjacent side-arms, the second arm being cut off 2 cm from the stopcock barrel, the third side-ami is cut at about 3 cm from the barrel. The tube attached to the bottom of the jacket is bent round till it is in the same plane as the jacket, side tube and stopcock. It is then cut off at a suitable length and gently adjusted so that the open end is close to the stopcock side-arm and exactly in line with it. These two ends are now joined together, using a thin rod to fill up the gap. 

Vacuum stopcocks are more expensive than those intended for use at ordinary pressures. The ground surfaces are more precise and the makers test their products for vacuum tightness before offering them for sale. One type of vacuum stopcock, shown in Fig. 11.11, has an oblique bore, which reduces the possibility of leakage through channels in the grease layer. The T-type and L-type, also shown in Fig. 11.11, are excellent for vacuum work. The keys of these types are held in place by atmospheric pressure when the apparatus is evacuated, and are therefore unlikely to be disturbed from their seatings when rotated. 

FIG. 11.11. Four common types of stopcock, (a) A stiaight stopcock witli a hollow key. (b) An oblique bore stopcock with a hollow key. (c) An L-type stopcock. Tlie key is a simple hollow cone with a hole drilled through it in hue with tlie side arm. (d) A T-type stopcock. The key is similar to that of (c) but tlie barrel has two side arms. This stopcock provides alternative paths for gas flow. 

NOTE THE 2 AND A MM OBLIQUE BORE VACUUM STOPCOCKS MAY BE REPLACED WITH TEFLON STOPCOCKS TO GOOD ADVANTAGE... 

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