90

TABLE 5 Temperature limits of secondary seal materials

TABLE 5 Temperature limits of secondary seal materials

removed from the unit. It is not necessary to use this procedure if a step in the sleeve or collar has been designed into the assembly to provide for proper seal setting. Assembling other parts of the seal will bring the unit to its correct working height.

All package or cartridge shaft seals can be assembled with relative ease because just the bolts at the gland plate and set screws on the drive collar need to be fastened to the seal chamber and shaft. After the seal spacer is removed, the unit is ready to operate.

To assemble a mechanical seal to a pump, a spacer coupling is required. If the pump is packed but may later be converted to mechanical seals, a spacer coupling should be included in the pump design.

Since a seal has precision-lapped faces and because secondary seal surfaces are critical in the assembly, installations to the equipment should be kept as clean as possible. All lead edges on sleeves and glands should have sufficient chamfers to facilitate installation.

When mechanical seals are properly applied, there should be no static leakage and, under normal conditions, the amount of dynamic leakage should range from none to just a few drops per minute. Under a full vacuum, a mechanical seal is used to prevent air from leaking into the pump. If excessive leakage occurs, the cause must be identified and corrected. Causes for seal leakage with possible corrections are listed in Table 7. In addition, Figure 48 illustrates the most common causes for mechanical seal leakage. Further information on seal leakage and the related condition of seal parts can be found in the works listed in the "Further Reading" section.

2.2.3 CENTRIFUGAL PUMP MECHANICAL SEALS TABLE 6 Frequently used seal face materials and their PV limitations

Sliding Materials Rotating Stationary

Carbon-graphite Ni-resist

Ceramic (85% Al2O3)

Ceramic (99% Al2O3)

Tungsten Carbide (6% Co) Tungsten Carbide (6% Ni)

Silicon Carbide

(converted

Carbon)

Silicon Carbide (solid)

Carbon-graphite Ceramic

Tungsten Carbide

Tungsten Carbide/ Silicon Carbide (solid)

Silicon Carbide

(converted carbon)

Silicon Carbide (solid)

100,000 Better thermal shock resistance (35.03) than ceramic

100,000 Poor thermal shock resistance and (35.03) much better corrosion resis tance than Ni-resist

100,000 Better corrosion resistance than

(35.03) 85% Al2O3 Ceramic

500,000 With bronze-filled carbon (175.15) graphite, PV is up to 100,000

lb/in2 ft/min (35.02 bar • m/s) 500,000 Ni binder for better corrosion (175.15) resistance

500,000 Good wear resistance; thin layer (175.15) of SiC makes relapping questionable

500,000 Better corrosion resistance than (175.15) Tungsten Carbide but poorer thermal shock resistance

500,000 Low PV, but very good against (17.51) face blistering

10,000 Good service on sealing paint

(3.50) pigments

120,000 PV is up to 185,000 lb/in2 ft/min

(42.04) (64.8 bar • m/s) with two grades that have different % of binder

300,000 Excellent abrasion resistance. (105.1) Commonly used on high temperature applications

500,000 Excellent abrasion resistance, (175.15) more economical than solid

Silicon Carbide 350,000 Excellent abrasion resistance, (122.6) good corrosion resistance and moderate thermal shock resistance

FIGURE 46 Common types of motion that influence seal performance
FIGURE 47 Typical installation reference dimensions

TABLE 7 Checklist for identifying causes of seal leakage

Symptom

Possible Causes

Corrective procedures

Seal spits and sputters ("face popping") in operation

Seal drips steadily

Seal fluid vaporizing at seal interfaces

Faces not flat Carbon graphite seal faces blistered Seal faces thermally distorted

Secondary seals nicked or scratched during installation O-rings overaged Secondary seals hard and brittle from compression set Secondary seals soft and sticky from chemical attack

Spring failure Hardware damaged by erosion Drive mechanisms corroded

Increase cooling of seal faces.

Check for proper seal balance with seal manufacturer

Add bypass flush line if not in use

Enlarge bypass flush line and/or orifices in gland plate

Check for seal interface cooling with seal manufacturer

Check for incorrect installation dimensions

Check for improper materials or seals for the application

Improve cooling flush lines

Check for gland plate distortion due to overtorquing of gland bolts

Check gland gasket for proper compression

Clean out foreign particles between seal faces; relap faces if necessary

Check for cracks and chips at seal faces; replace primary and mating rings

Replace secondary seals

Check for proper lead-in chamfers, burrs, and so on

Check for proper seals with seal manufacturer

Check with seal manufacturer for other material

Replace parts

Check with seal manufacturer for other material

(continues)

TABLE 7 Continued.

Symptom Possible Causes Corrective procedures

TABLE 7 Continued.

Symptom Possible Causes Corrective procedures

Seal squeals

Amount of liquid

Add bypass flush line if not in use

during operation

inadequate to

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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