Mechanical pump, roughing

After shutting off the roughing and fore pumps, open Stopcocks 5 and 6 to vent the pumps (this action prevents the mechanical pump oil from accidentally being sucked into the vacuum line). 

Low pressures can be achieved in a mechanical or "roughing" pump, by using a fluid (water, mercury, oil) in a rotating-vane technique to adsorb molecules within the fluid when exposed to the container to be evacuated, then expelling these molecules to the laboratory when the vane has brought the fluid into contact with laboratory air. 

Roughing pump n. In high-vacuum work, e.g., vacuum metallizing, a mechanical pump that removes most of the air from the chamber, leaving the remainder to a secondary pump, usually a diffusion pump, capable of reducing the pressure to about 0.13 Pa absolute. 

Mechanical pump (vacuum technology) A compression-type vacuum pump with moving parts. The term is generally applied to pumps used for roughing or backing (Example oil-sealed mechanical pump, piston pump, diaphragm pump, etc.) and not high vacuum pumps (Example turbomolecular pumps). See also Vacuum pump. 

The most common mechanical pump is the oil-sealed rotary pump. They are commonly used to obtain the rough vacuum (10 to 10 torr or 10 to 100 pm) required to support other pumps. They are simple, reliable, and common, and can obtain pressures as low as 1 x 10 " torr in exceptional circumstances. 

Modem UHV chambers are constmcted from stainless steel. The principal seals are metal-on-metal, thus the use of greases is avoided. A combination of pumps is nomially used, including ion pumps, turbomolecular pumps, cryopumps and mechanical (roughing) pumps. The entire system is generally heatable to 500 K. This bakeout for a period of... 

Because of the low efficiency of steam-ejector vacuum systems, there is a range of vacuum above 13 kPa (100 mm Hg) where mechanical vacuum pumps are usually more economical. The capital cost of the vacuum pump goes up roughly as (suction volume) or (l/P). This means that as pressure falls, the capital cost of the vacuum pump rises more swiftly than the energy cost of the steam ejector, which iacreases as (1 /P). Usually below 1.3 kPa (10 mm Hg), the steam ejector is more cost-effective. 

Most induction ac motors are fixed-speed. However, a large number of motor applications would benefit if the motor speed could be adjusted to match process requirements. Motor speed controls are the devices which, when properly applied, can tap most of the potential energy savings in motor systems. Motor speed controls are particularly attractive in applications where there is variable fluid flow. In many centrifugal pump, fan, and compressor applications mechanical power grows roughly with the cube of the fluid flow. To move 80 percent of the nominal flow only half of the power is required. Centrifugal loads are therefore excellent candidates for motor speed control. Other loads that may benefit from the use of motor speed controls include conveyers, traction drives, winders, machine tools and robotics. 

In all protein-protein complexes studied to date in which cytochrome c has been a partner, it has been shown that the ET rates depend strongly on the reaction driving force. It follows that variations in the reorganization energy could control ET rates in these cases [12]. In redox enzymes with two or more active centers, ET between two centers could be turned on by lowering X at roughly constant — AG [1]. Indeed, a proposal has been advanced that this type of mechanism would be an efficient way to gate the electron flow in a redox-linked proton pump such as cytochrome oxidase [75]. 

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