Seal Selection

Chapter from the Pumps & Hydraulics Design Guide.

MECHANICAL SEAL SELECTION — API 682

Seal Type Classification

Seal Type	Arrangement	API 682 Code	Description	Temperature Limit	Pressure Limit	Typical Applications	Flush Plan
Type A	1 (single)	1CW-FX	Single cartridge, fixed	500°F	400 psig	Clean hydrocarbon	Plan 11 or 32
Type A	1 (single)	1CW-FL	Single cartridge, floating	500°F	400 psig	Moderate duty	Plan 11
Type B	2 (dual unpressurized)	2CW-CW	Dual, containment	500°F	400 psig	Toxic / hazardous	Plan 52 or 72
Type B	2 (dual unpressurized)	2CW-CS	Dual, contacting	500°F	400 psig	Moderate hazard	Plan 52 or 76
Type C	3 (dual pressurized)	3CW-FB	Dual, pressurized barrier	500°F	400 psig	Lethal / zero emission	Plan 53A, 53B, or 53C
Type C	3 (dual pressurized)	3CW-BB	Dual, pressurized barrier	500°F	400 psig	High hazard, high T	Plan 54

Seal Plan Selection Guide

Plan	Description	Application	Advantages	Limitations	Flow/Pressure	Typical Service
Plan 11	Internal flush from discharge	Clean, cool service	Simple, no external utilities	Limited cooling	Recirculation from pump	Clean hydrocarbon, water
Plan 13	Reverse flush from seal to suction	Clean, low ΔP	No throat bushing needed	Low flush flow	Seal chamber to suction	Low pressure, clean service
Plan 21	External flush from discharge + cooler	Hot service	Temperature control	Requires cooler	Pump discharge through cooler	Hot oil, heavy HC
Plan 23	Internal + cooler recirculation	Hot clean service	Good cooling, no throat bushing	Requires cooler, pumping ring	Internal circ through cooler	Hot clean hydrocarbon
Plan 32	External flush from clean source	Dirty service	Clean flush to seal faces	Requires external source	External clean fluid supply	Slurry, dirty HC, catalyst
Plan 52	Unpressurized buffer fluid	Dual unpressurized	Leak detection, buffer	Not zero emission	Buffer pot, thermosiphon	Toxic HC, H2S service
Plan 53A	Pressurized barrier, accumulator	Dual pressurized	Zero process emission	Bladder accumulator maint	N2 pressurized accumulator	Lethal service
Plan 53B	Pressurized barrier, piston	Dual pressurized	Follows seal chamber P	More complex	Piston-tracked pressure	Variable pressure service
Plan 53C	Pressurized barrier, ext pump	Dual pressurized, high flow	High barrier flow	External pump required	Forced circulation	High heat generation seals
Plan 54	Pressurized barrier, external	Dual pressurized	Continuous barrier supply	Requires external system	External pressurized supply	Critical lethal service

Seal Selection Decision Framework

Step 1: Classify fluid hazard level (non-hazardous / hazardous / toxic / lethal)
Step 2: Determine seal arrangement:
• Non-hazardous → Arrangement 1 (single seal)
• Hazardous → Arrangement 2 (dual unpressurized) minimum
• Toxic/Lethal → Arrangement 3 (dual pressurized) required
Step 3: Select seal type (A/B/C) based on arrangement and service
Step 4: Select flush plan based on process conditions:
• Clean & cool → Plan 11
• Clean & hot → Plan 21 or 23
• Dirty → Plan 32
• Dual unpressurized → Plan 52 or 72
• Dual pressurized → Plan 53A/B/C or 54
Step 5: Select barrier/buffer fluid (compatible, non-contaminating)
Step 6: Specify face materials (carbon vs SiC vs TC) and elastomers (Viton, Kalrez, EPDM)

Source: Pumps_Hydraulics_Design_Guide_v1.xlsx · sheet “Seal Selection”

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