A mechanical seal is only as good as its support system. The seal faces run on a thin fluid film — 1 micron thick. If that film is too hot, too cold, too dirty, or at the wrong pressure, the seal fails. API 682 defines standard auxiliary plans (Plan 01 through Plan 74) that control seal environment. Selecting the right plan for your OH2 pump determines whether the seal lasts 3 years or 3 months.
This guide covers the most common API 682 auxiliary plans for API 610 OH2 pumps, including heat tracing, reservoirs, and flush systems.
Why Seal Support Systems Matter
The mechanical seal faces generate heat from friction. For a typical 100 mm seal at 3,000 rpm, heat generation is 2–5 kW. Without cooling, the seal faces reach 200°C+ in minutes. The faces warp. The elastomer hardens. The seal leaks.
The seal support system does three things:
- Cools the seal: Removes friction heat, keeps faces below 80°C
- Cleans the flush fluid: Filters solids, prevents abrasion of seal faces
- Controls pressure: Maintains correct pressure at seal faces, prevents vaporization
Without a support system, even the best mechanical seal fails in weeks. With the right system, the same seal lasts 3–5 years.
API 682 Auxiliary Plans: The Common Ones
API 682 defines over 30 auxiliary plans. For OH2 pumps, these are the most common:
Plan 11: Internal Recirculation (Single Seal)
How it works: Process fluid is tapped from the pump discharge, flows through an orifice, and enters the seal chamber. The fluid flushes the seal faces, then returns to the pump process. No external equipment needed.
When to use: Clean, non-abrasive fluids at moderate temperature (below 80°C). The most common plan for general OH2 service.
Limitations: Does not cool the seal (fluid is at process temperature). Does not filter solids. Not suitable for dirty or hot fluids.
Plan 21: Recirculation with Cooler (Single Seal)
How it works: Same as Plan 11, but the flush fluid passes through a heat exchanger before entering the seal chamber. The cooler reduces flush temperature by 20–40°C.
When to use: Hot fluids (80–200°C). The cooler keeps seal faces below 80°C.
Limitations: Requires cooling water supply. The cooler must be maintained (fouling reduces cooling efficiency).
Plan 23: Recirculation with Cooler (Closed Loop)
How it works: A closed loop of clean fluid circulates through the seal chamber and a cooler. A pumping ring (on the seal) drives circulation. No process fluid enters the seal chamber — the seal runs on clean, cool fluid.
When to use: Hot, dirty, or polymerizing fluids. The closed loop keeps the seal clean and cool. Standard for refinery hot oil pumps.
Advantages over Plan 21: Seal never sees process fluid (cleaner environment). Lower flush flow rate (more efficient).
Plan 32: External Flush (Single Seal)
How it works: Clean fluid from an external source (a separate tank or another pump) flushes the seal chamber. The external fluid is compatible with the process fluid.
When to use: Dirty or abrasive process fluids (slurry, polymers). The clean flush keeps solids away from seal faces.
Limitations: Requires a reliable external flush source. The flush fluid mixes with process fluid — must be compatible.
Plan 53A/B/C: Pressurized Barrier (Double Seal)
How it works: A barrier fluid (clean, compatible) fills the space between two seal faces. The barrier fluid is pressurized above process pressure. If the inner seal fails, barrier fluid leaks into the pump (not process fluid out). A reservoir maintains barrier fluid pressure and level.
When to use: Hazardous, toxic, or valuable fluids where zero leakage is required. Standard for refinery and chemical plant critical service.
Plan 53A: Gas-pressurized reservoir (nitrogen or air). Simple, reliable.
Plan 53B: Piston accumulator or bladder accumulator. More compact, better pressure control.
Plan 53C: Piston accumulator with pump charging. For high-pressure service.
Heat Tracing for Seal Systems
For fluids that solidify or become highly viscous at low temperature (heavy oil, wax, polymers), the seal system must be heat-traced. If the fluid cools, it solidifies in the seal chamber. The seal seizes.
Heat tracing methods:
1. Steam tracing: Steam lines wrapped around the seal chamber and flush piping. Maintains temperature above the fluid's pour point. Common in refineries (steam is readily available).
2. Electrical tracing: Electric heat tape wrapped around piping. Self-regulating (adjusts heat output based on temperature). More precise than steam. Common where steam is not available.
3. Jacketed seal chamber: The seal chamber has a double wall with hot fluid (steam or hot oil) circulating in the jacket. Most effective for very viscous fluids.
Design considerations:
- Tracing must cover the entire seal system: seal chamber, flush piping, cooler, reservoir
- Temperature must be maintained above the fluid's pour point + 10°C margin
- Insulation is required — without it, heat loss exceeds tracing capacity
- Temperature sensors with alarms prevent overheating or underheating
Reservoirs for Double Seal Systems
For Plan 53A/B/C double seals, a barrier fluid reservoir is required. The reservoir:
- Stores barrier fluid (5–20 liters typical)
- Maintains pressure above process pressure (typically 1–2 bar above)
- Provides cooling (reservoir has a cooling coil)
- Monitors level (low level alarm indicates seal failure)
- Monitors pressure (pressure loss indicates system leak)
Reservoir design:
- Vertical cylindrical tank (150–300 mm diameter, 500–800 mm height)
- Level gauge (sight glass or electronic)
- Pressure gauge (with alarm switch)
- Cooling coil (water-cooled, maintains barrier fluid below 50°C)
- Fill port and drain port
- Gas connection (for Plan 53A pressurization)
Barrier fluid selection: Must be compatible with both the process fluid and the seal elastomer. Common barrier fluids: clean water (for water-compatible processes), synthetic oil (for hydrocarbon processes), propylene glycol (for low-temperature service).
Selecting the Right Plan for Your OH2 Pump
| Fluid Condition | Recommended Plan | Seal Type |
|---|---|---|
| Clean, cool (<80°C), non-hazardous | Plan 11 | Single mechanical seal |
| Clean, hot (80–200°C), non-hazardous | Plan 21 or 23 | Single mechanical seal |
| Dirty or abrasive, cool | Plan 32 (external flush) | Single mechanical seal |
| Dirty or abrasive, hot | Plan 23 + Plan 32 | Single mechanical seal |
| Hazardous or toxic, any temperature | Plan 53A/B/C | Double mechanical seal |
| Very hazardous (zero emission required) | Plan 53B + containment seal | Double + containment (triple) |
| Polymerizing or solidifying | Plan 23 + heat tracing | Single or double |
Common Seal Support System Mistakes
Mistake 1: Plan 11 for hot fluid. The flush fluid is at process temperature (150°C). The seal faces run at 170°C. Elastomer hardens. Seal fails in 3 months. Right answer: Plan 21 or 23 with cooler.
Mistake 2: No heat tracing for heavy oil. The fluid cools and solidifies in the seal chamber. The seal seizes. Right answer: steam or electric tracing on all seal piping.
Mistake 3: Plan 53A with wrong barrier fluid. The barrier fluid is incompatible with the process. If the inner seal fails, barrier fluid contaminates the process. Right answer: verify barrier fluid compatibility before filling.
Mistake 4: No level alarm on reservoir. The inner seal fails. Barrier fluid leaks into the pump. Reservoir level drops. Nobody notices. The outer seal then runs dry and fails. Process fluid leaks to atmosphere. Right answer: low-level alarm on reservoir.
Mistake 5: Cooler not maintained. The cooler fouls. Cooling capacity drops. Seal temperature rises. Seal fails. Right answer: inspect and clean cooler annually.
For API 610 OH2 pump seal support system selection and design, our API 610 OH2 pump range can be configured with any API 682 auxiliary plan. For seal plan recommendation, talk to our engineers with your fluid properties and operating conditions.