Spring-mounted pump

The mechanical vacuum pump consists of an eccentrically mounted rotor driven inside a cylindrical housing. Two types of mechanical pumps are constructed (a) the rotary piston type, where the rotor comes in close contact with the housing and thus makes the seal between intake and exhaust compartments, and (b) the vane type pump where two vanes, spring-mounted in the rotor, make contact with the walls of the housing and thereby divide the space between the rotor and the housing. Typical construction is shown in Figs. 2 and 3. 

This type of seal has the rotary component and face mounted outside the seal chamber. The springs and drive elements are outside the pumped liquid. This reduces the problems associated with corrosion and the accumulation of pumped product clogging the springs. This seal is popular in the food processing industry. The pumped liquid arrives to the inside diameter of the faces and seals toward the outside diameter. The environment outside the pump approaches the OD of the face union. Pressures are limited to about 35 psig. Sometimes this. seal can be mounted either inside or outside the pump. This seal is easy to install, adjust, and maintain. It permits easy access and cleaning of the pump internal parts, often required in the food processing industry. 

This dial indicator is fixed to the volute mounting adapter collar of the pump and the needle is on the shaft (Figure 14-21). The shaft should be moved radially by hand (see the arrows) up and down. Note the movement in the indicator. This is a check of the radial tolerance in the bearing. Some people use the word run out . Radial dellection causes misalignment of the rotating and stationary faces of the mechanical seal. This shortens the seal life by eausing drive pins and springs to wear and rub in relative motion. 

To further minimize possible pressure pulsation, the pumps can be installed together with a pulsation dampener mounted at the discharge. Pulsation dampeners are air pressurized or spring loaded to ensure a smoother product flow in the process line. Slow rotational speed of the pump s crankshaft also helps to minimize pressure pulsation. 

Once mounted (samples are usually held down by clips or inserted into spring loaded sample holders), the samples can be introduced into an introduction chamber. These tend to be of a minimal size to allow for quick pump down, with pump-down times typically in the 10-15 min range for clean samples of low porosity. In the case of highly porous samples, it is advisable to pump these down in the introduction chamber for extended periods of time (overnight before analysis may be required). 

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