Break-seal valves

For preparatory work, the rather expensive Bodenstein valves may frequently be replaced by a combination of fusing of connections (closure) and break-seal valves (opening), if it is sufficient to open or close a connection only once. 

Fig. 33. Break-seal valves magnetically operated hammer bar.

Fig. 34. Briscoe break-seal valve. The capillary point S is still open during sealing to side 1, but several scratches have been made at a. Then h is fused by means of a very small flame introduced through o, with air entering at d. Next the valve is sealed to the other side, the Hg-filled hammer bar is carefully introduced and d is sealed. A sharp movement applied from the outside will shatter the valve.

Fig. 99. Preparation of DI. A) 5-liter flask with catalyst B) break-seal valve ...

Fig. 100. Preparation of DgS. F-, ampoules containing SO3 Ai, containers for SO3 ampoules K, K ) seal breakers MMg, Mg) electromagnets H) break-seal valve 0, D, F) receivers (can be cooled) G, L) sealing points.

In the same way, but using break-seal valves, Goodeve and Richardson prepared ClgOg of an especially high degree of purity. 

Fig. 298. Preparation of titanium (IV) iodide according to Fast d, e and f are break-seal valves g is a steel ball.

In this section only those taps and valves will be considered which are suitable for repeated use. Break-seals and seal-off points which can be considered as once-only valves are discussed in Section 3.2. Before discussing the different types of taps and valves there is a safety rule which applies to all taps which are operated by turning a key Always use two hands one hand to hold the tap barrel and the other to turn the key. 

The long-term storage of liquids and gases is best accomplished in an ampule or bulb fitted with a break-seal. Once the sample is sealed off in such a container, leakage is no problem as it would be if a stopcock or valve were used. Furthermore, this practice is economically sound, since a break-seal is much less expensive than a stopcock or valve. 

The difficulties created by stopcocks and valves can usually be minimized. However, it is occasionally necessary to completely eliminate these sources of leakage and contamination by the use of break-seals and vacuum seal-offs. Typical situations in which sealed tube techniques are widely used are quantitative hydrolysis and oxidation reactions which require elevated pressures and temperatures, precise physical measurements on highly reactive organometallic compounds, long-term storage of reactive samples, and nonaqueous reactions under high pressure (for example, SO2 or NH3 at room temperature). Each piece of apparatus must be constructed to meet a specific need, so it is not possible to outline an apparatus which is of general use. Nevertheless, several examples will be presented here which serve to indicate the approach. 

Break-seals (Fig. 9.31) are commonly used on sealed reaction and storage tubes because this type of seal allows recovery of volatile materials. The type illustrated in Fig. 9.31a may be opened in an apparatus which contains an off-center arm which may be rotated to break the small tube (Fig. 9.32a). Among the many variants of this design of tube opener, one by Mahler and Velmey is constructed from a /4-in. stainless-steel needle valve which is drilled out to receive the break-seal so that the valve stem may be screwed down on the small tube (Fig. 9.32b).59 The break-seal and vacuum system are connected to this... 

Wliile all the flame arrester types disenssed above have a solid arresting element (matrix), the hydranlic (liqnid seal) flame arrester contains a liqnid, nsnally water, to provide a flame barrier. It operates by breaking np the gas flow into discrete bnbbles by means of an internal device to qnench the flame. A mechanical nonretnrn valve (check valve) is sometimes incorporated to prevent the displacement of liqnid dnring or after a flame event (deflagration or detonation). 

Packing glands or seals on pumps and compressors Pipe flanges, fittings and valve stems Threaded fittings that are not seal-welded Sample stations with an air break Manways and piping connections to vessels Piping to equipment connections... 

The principle of all aerosols is that a liquefied gas in a pressurised container will provide a constant pressure while the container is being emptied. The essential components of an aerosol beside the container itself are the product, propellant, and valve assembly. The valve is designed to dispense the product in the required manner while maintaining both the product and propellant hermetically sealed until the product is expended. The fact that the product is sealed in the container and protected from air and other outside contaminants has obvious advantages in the field of pharmaceuticals. The intimate mixture of propellant and product in a true aerosol results in a rapid expansion of the propellant as it leaves the valve orifice. This breaks up the product into small particles giving a fine mist, coarse spray, foam, or dust according to the nature and relative quantity of the product and the propellant and the type of valve. 

This valve (Figure 8-6, p. 88) attaches to the main condenser. It permits attachment of a sample to the condenser without breaking the vacuum seal on the other sample holders. Samples also can be removed in the same way. The white valve stem on the front is turned to control the operation. The valve usually is made of a rather hard rubber with a plastic inner stem. It also includes an internal baffle to prevent cross contamination from one sample to another. It can be taken apart for cleaning. 

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