Page 538 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Dry Gas Seal Best Practices Be st Practice 9.1

Fig 9.1.11 Tandem seal (Courtesy of Flowserve Corp.)

Fig 9.1.12 Tandem seal and barrier seal typical housing arrangement

dry gas system, does not enter the seal chamber, velocities across additional barrier seal is used and provided with pressurized
the labyrinth should be maintained between 6e15 m/sec (20e50 nitrogen at approximately 35 kPa (5 psi).
ft/sec). It is the writer’s experience that considering labyrinth A typical seal system for this arrangement is shown in
wear, the design should be closer to 15 m/sec (50 ft/sec). Figure 9.1.13. As previously mentioned, dry gas seal reliability
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Approximately 1.7e3.4 Nm /hr (1e2 scfm) flow (standard depends on the condition of the gas entering the seal faces. The
cubic feet per minute) leak across the first tandem seal faces function of the seal gas supply system for any dry gas seal option
(primary seal) and exit through the primary vent. Based on the is to continuously supply clean, dry gas to the seal faces. During
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backpressure of the primary vent system, 1.7 Nm /hr (1 scfm) start-up, when the compressor is not operating with sufficient
or less will pass through the second tandem seal faces (sec- pressure to supply the seals, an alternate source of gas or a gas
ondary seal) and exit through the secondary vent. To ensure that pressure booster system should be provided. These items are
oil mist from the bearing housing does not enter the dry gas seal shown in Figure 9.1.13 and are typical for any type of dry gas
chamber and that seal gas does not escape to atmosphere, an seal application. Note that the following options exist regarding

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