833

Source: Flowserve Corporation

Source: Flowserve Corporation falls off as the rings wear. Table 3 shows some of the effects of increasing the clearance of rings similar to Figure 12a.

The labyrinth construction shown in Figure 12b has been used to increase the leakage path without increasing the axial length of the rings. If the pressure differential across these rings is high enough, the pump shaft may take on lateral vibrations with relatively large amplitude and long period, which can cause serious damage. One remedy for these vibrations is to increase clearance 2 in Figure 12b relative to clearance 1, at the expense of an increased leakage flow. High-pressure breakdown through plain rings may cause vibra-tion,10 but this is not usually a serious problem. It is considered good practice to replace or repair wearing rings when the nominal clearance has doubled. The presence of abrasive solids in the liquid pumped may be expected to increase wearing-ring clearances rapidly.

vane-tip clearance Many impellers are made without an outer shroud and rely on close running clearances between the vane tips and the casing to hold leakage across the vane tips to a minimum. Although this construction usually is not used with pumps having specific speeds less than about 6000 (2.20), Wood et al.11 have reported good results with semi-open impellers at 1800 (0.66) £ ns £ 4100 (1.50). It appears that both head and efficiency increase with decreasing tip clearance and are quite sensitive to rather small changes in clearance. Reducing the tip clearance from about 0.060 in (1.5 mm) to about 0.010 in (0.25 mm) may increase the efficiency by as much as 10%. Abrasive solids in the liquid pumped probably will increase tip clearances rapidly.

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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