Dry Gas Seals

Chapter from the Pumps & Hydraulics Design Guide.

DRY GAS SEAL FUNDAMENTALS

Seal Configuration Types

Configuration	Arrangement	Application	Gas Supply	Vent/Flare	Monitoring	Advantages	Limitations
Single	One seal, process side	Non-toxic, non-flammable	Filtered process gas or N2	Primary vent to safe location	Leakage flow	Simple, low cost	Requires safe vent location
Tandem	Two seals in series	Most refinery applications	Primary: process gas Secondary: N2 buffer	Primary vent: flare Secondary: atmosphere	Primary + secondary leakage	Redundancy, zero emission at secondary	Higher cost, more gas supply
Double Opposed	Two seals face-to-face	Toxic / sour gas service	Inert barrier gas (N2) between seals	Both seal leakages to flare	Barrier pressure, both leakage flows	Complete isolation of process gas	Highest cost, continuous N2 supply

Gas Supply Requirements

Parameter	Requirement	Typical Value	Consequence of Failure
Gas Quality	Clean, dry, no liquids	<3 micron filtration	Face damage, seal failure
Supply Pressure	Above seal chamber P	15-25 psig above reference	Loss of gas film, contact
Flow Rate	Per manufacturer	5-50 SCFM typical	Insufficient film, overheating
Temperature	Below max for O-rings	<250°F typically	Elastomer degradation
Dew Point	Below minimum operating T	-40°F or lower	Condensation damages faces
Separation	Coalescer + filter	Dual coalescer filters	Liquid carryover destroys seal

Monitoring & Alarm Parameters

Primary Seal Leakage: normal <5 SCFM, alarm at 10 SCFM, trip at 20 SCFM (typical)
Secondary Seal Leakage: normal <1 SCFM, alarm at 3 SCFM, trip at 5 SCFM
Barrier Gas Pressure: alarm on low ΔP (loss of barrier)
Seal Gas ΔP: alarm on high ΔP (filter plugging)
Seal Cavity Temperature: alarm on high temperature

Trending: plot primary leakage rate daily — gradual increase indicates face wear
Sudden increase: possible face damage, contamination event, or O-ring failure

Source: Pumps_Hydraulics_Design_Guide_v1.xlsx · sheet “Dry Gas Seals”

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