Electric diaphragm pumps

Various oil-free electric diaphragm pumps can be used to provide vacuum levels down to about lOmmHg. Some models are Teflon lined (e.g. KNF, Vacuubrand, Divac) and designed to withstand solvent vapours, and these 

For some tasks very cheap and simple fish tank-type diaphragm pumps are useful. These will produce a vacuum of about SOOmmHg and can also be used to provide compressed air for pressurizing chromatography columns (see Chapter 11). 

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Most often, the sludge is pumped to a collection tank before going on to final disposal. Advancing-cavity pumps and diaphragm pumps operated by air or electricity are in common use, and in larger units, centrifugal slurry pumps are the norm. 

We have to make a distinction here between electric controllers (e.g. PID controllers) with a proportional valve as actuator and mechanical diaphragm controllers. In a regulation system w/ith electric controllers the coordination between controller and actuator (piezoelectric gas inlet valve, inlet valve A/ith motor drive, butterfly control valve, throttle valve) is difficult because of the very different boundary conditions (volume of the vessel, effective pumping speed at the vessel, pressure control range). Such control circuits tend to vibrate easily when process malfunctions occur. It is virtually impossible to specify generally valid standard values. 

These pumps can be designed with or without a diaphragm. Their operation involves the same mechanism as a cam-drive piston pump, but the movements of the piston are achieved by passing (or not) an electric current through a coiled resistor around the piston [29]. As the solenoid-driven displacement is very abrupt, the pump delivers a pulsed flow [30]. 

The excellent electrical insulation properties and chemical inertness over a wide temperature range account for the two main fields of use of polytetrafluoroethylene, namely electrical and chemical applications. Electrical applications include wire coatings, holders and spacers for use in aggressive conditions whilst chemical applications include gaskets, pump parts and laboratory equipment. Other uses include non-stick coverings for kitchen utensils, low-friction linings for hoppers, and diaphragms for low temperature equipment. 

Piston displacement driven by electric motor Figure 5.4 Principle of modern diaphragm vacuum pump. 

Examples of actuators are rheostats to set and control electrical current, valves, flaps, and metering pumps for liquids. The actuator, which is most frequently encountered in chemical process engineering, is the diaphragm valve (Figure 12.29). 

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