Taps, greasing

No greased taps or connections were employed. Nupro bellows valves (Section VI,A) were employed ahead of the catalyst and Teflon needle valves following it. Access to the saturator was provided by a miniature Ipatieff closure of stainless steel in which a copper disk was compressed between two raised circular ridges. 

Pflug and Benson have described an accurate dilatometer based on the design of Geffcken, Kruis, and Solana. The volume of added component is determined from the mass of mercury displaced in a piston-type arran ment. Because the liquids pass through a greased tap its use is limited. Chareyron and Clechet have described a similar apparatus. 

Another modification by Bottomley and Scott,shown in Figure 19, eliminates all grease taps. On tilting the dilatometer mercury flows from the tip... 

In filling the tube R, one tap is inserted after being carefully greased with a high-vacuum or silicone grease. The taps are provided with scored grooves (that run completely around them near their outer end) which act as a trap to prevent... 

The ground runs are greased witli vaseline or a mixture of bees-wax and vaseline, and the ail is exhausted by attaching the tube of the watei-pump to the glass tap of the desiccator. 

Bromine trifluoride, though it reacts explosively with water and hydrocarbon tap greases, is somewhat less violent and vigorous a fluorinat-ing agent than is CIF3. The sequence of reactivity usually quoted for the halogen fluorides is ... 

Mercury cut-offs are used in vacuum apparatus instead of taps when tap grease is undesirable. A frequently used type is shown in Figure 63. A two-way tap is attached at the top of a reservoir for mercury. 

Measure 5 mL of tap water into the graduated cylinder. Pour the water into one of the test tubes. Use the grease pencil to mark the test tube at the 5-mL level. Discard the water. Repeat for the other two test tubes. 

Storage of monomers and solvents also requires special precautions. The vessels must be specially constructed and be closed with a self-sealing cap through which the distilled contents can be transferred with a pipette or hypodermic syringe under inert gas. The contents should also not come in contact with tap grease. 

In the schematic diagram of the vacuum line (Fig. 2.1) a U-bend is shown between the main tap T, and the manifold, which has two functions (a) It lends an extra element of mechanical flexibility to the system by absorbing small movements at the traps or along the main manifold (WL or WL ) which might otherwise lead to fracture and (b) it acts as a sink for non-volatile residues in the line and for grease which may be washed away from the taps 7, 7 and 7. ... 

Glass taps Glass taps should only be used at the pumping end of a vacuum system or where there is no likelihood of them coming into contact with liquids since, whatever grease is used, it will tend to be washed away... 

Fig. 2.5. How to grease a tap key. As shown, the grease (shaded areas) is applied in two small patches above and below each hole and in two streaks mid-way between the holes.

Within the working part of the vacuum system the use of all-metal valves is not common indeed, since the advent of PTFE taps there are few occasions when such taps are necessary. Nevertheless, it is worthwhile to note that suitable taps do exist for operations involving materials incompatible with both PTFE and grease, or if a good static vacuum (see Section 2.3.1) is required for a long time in circumstances where a glass tap would be inappropriate. 

---