Floating Ring Design

A segmented throttle bushing made of many floating rings will enable conformity with the radial shaft movement and smaller running clearances to reduce seal leakage. The construction of a floating ring stuffing box (see Figure 2) varies from one pump manufacturer

FIGURE 2 Floating ring seal design with shaft sleeve. Pegs prevent rotation of spring-loaded rings but let them float radially. (From Power, August 1980, McGraw-Hill, New York, copyright 1980)

to another, but the unit basically consists of a stack of hardened, martensitic stainless steel rings (typically 17 percent chrome), instead of a stationary bushing. The rings run against a smooth, hardened, martensitic stainless steel (typically 12 to 17 percent chrome) rotating shaft sleeve surface.

The separate rings are all contained within a housing installed in the pump casing end cover. Each ring is loaded against an adjacent stainless steel ring spacer so that a stationary seal is produced in the axial direction, but the ring is still able to move radially with the shaft. An axial loading of the rings is provided by hydraulic pressure during operation and by springs during idle pump periods. The rings are locked against rotation usually by pegs and/or a slot arrangement.

A small radial clearance, usually 0.001 to 0.0015 in per inch (0.001 0.0015 mm per mm) of the shaft diameter, is provided between the rings and the shaft sleeve to provide an adequate throttling of seal leakage across the limited number of seal rings. The length of each ring varies with the diameter of the injection-type seal but is generally about 0.50 in (13 mm). The radial clearance enables a reduced injection flow but increases the sensitivity of the seal to foreign particles in the seal leakage.

The individual seal rings are permitted to move radially (float), finding an equilibrium running position relative to the shaft. The capability to float up to .016 in (.4 mm) radially increases the tolerance for shaft misalignment as the shaft passes through the seal area. The multiplicity of seal rings further reduces the effect of any angular displacement between the rotating and stationary components that might arise from errors in the original assembly or from distortions caused by temperature changes during pump load variations.

Some injection-type shaft seal designs use a combination of serrations and floating rings in the same stuffing box. For either type of seal, careful maintenance during the assembly or disassembly requires accurate alignment of the rotating and stationary components as well as careful handling to avoid scratching the components. Cleanliness is of utmost importance with shaft seals.

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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