Internal clearance

AU processed material is screened to return the coarse fraction for a second pass through the system. Process feed rates are matched to operating variables such as rpm speed and internal clearances, thus minimizing the level of excess fines (—200 mesh (<0.075 mm mm)). At one installation (3) the foUowing product size gradation of total smaller than mesh size (cumulative minus) was obtained ... 

Presence of Solids When a pump is required to pump a hquid containing suspended solids, there are unique requirements which must be considered. Adequate clear-liquid hydraiilic performance and the use of carefully selected materials of construction may not be all that is required for satisfacdoiy pump selection. Dimensions of all internal passages are critical. Pockets and dead spots, areas where solids can accumulate, must be avoided. Close internal clearances are undesirable because of abrasion. Flushing connections for continuous or intermittent use should be provided. 

Rotary Pumps In rotary pumps the liquid is displaced by rotation of one or more members within a stationary housing. Because internal clearances, although minute, are a necessity in all but a few special types, capacity decreases somewhat with increasing pump differentia pressure. Therefore, these pumps are not truly positive-displacement pumps. However, for many other reasons they are considered as such. 

S" = Slip, quantity of fluid that leaks through internal clearances of rotary pump per unit time, GPM SpGr = Specific graHty of liquid at pumping temperature referred to water =1.0 s = Stroke, in. 

Internal slip is simply the amount of gas that can flow through internal clearances from the discharge back to the inlet. Obviously, internal wear will increase internal slip. 

Note Depending on pump design, the first or second wet lateral critical speed of multistage and high-speed pumps may coincide with the operating speed, particularly as internal clearances increase with wear. A lateral analysis can predict when this coincidence is likely and whether the resulting vibration will be acceptable. 

ISO 4200, Plain end steel tubes, welded and seamless—General tables of dimensions and masses per unit length. ISO 5753, Rolling bearings— Radial internal clearance. 

NOTE Cooling the outer ring can reduce bearing internal clearance and cause bearing failure. 

There are small internal clearances (< 1mm usually) between the rotors and the housing and between the rotors themselves. Relatively low pressures (in the medium vacuum range) can, however, be achieved. Importantly, there is no oil sealing in the gas-handling part of the pumps. The nominal (theoretical) pumping speed (iSth) of a Roots pump is ... 

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