Diffusion pumps draining

After the cleaning has been completed, it may be necessary to remove the end of the drainage tube to remove any burnt deposit. Then, add an extension of the draining tube and close it off at about 1 to 1 V2 in. (see Fig. 7.26). Now the pump can be refilled. The reason for cutting the drain tube in half (as mentioned) is to provide distance from the diffusion pump onto which you can fuse an extension. If an extension were to be sealed directly onto the pump, extensive and formal annealing of the pump would be required. 

The cleaning of a mercury diffusion pump is somewhat simpler because mercury does not break down as most pump oils do. However, mercury gets dirty, and a dirty mercury pump still needs to be cleaned. After you have drained the mercury out of a glass diffusion pump, refill the pump with approximately a 6 molar nitric acid solution and let it sit until the mercury has been removed. Do not pour this liquid down the sink Check with local waste management and/or your health and safety officer. The pump should be flushed with distilled water and then rinsed with methanol for drying. 

The drain tube must be cut in half to permit the draining of the diffusion pump oils. 

Finally, add an extension onto the draining tube before refilling the diffusion pump. 

Fig. 7.26 The procedure for closing the drain tube on a glass diffusion pump.

A drawing of the cross section of a Dewar vessel is shown in Figure 2 [1]. It shows the basic elements of a high performance cryogenic storage vessel. A fill and drain line is provided at the bottom of the vessel to transfer fluid in and out of the tank. Liquid can be removed either by pressurization of the inner vessel with a pressurization gas or by a liquid pump. A vapor vent line is located near the top of the vessel to allow vapor formed from heat leak to escape. This line can also be used to introduce a pressurization gas. If pressurization is used to force liquid from the tank, a diffuser is provided to distribute the pressurization gas in the vapor space away from the surface of the cold liquid. This prevents the unwanted condensation of the warm pressurization gas by the cold liquid surface. 

Brining This step involves the injection of brine into the resin bed. A brine maker or day tank is used to dissolve salt into a 25% solution. This solution is then diluted in line with service water to 10% and either pumped or educted into the resin bed. Flow rates range from 0.5 to 1.0 gpm/ftl The low flow rate is necessary to give ions time to diffuse into and out of the resin beads. Duration of backwash is typically 20 to 30 minutes. Effluent is sent to drain. 

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