Views: 0 Author: Site Editor Publish Time: 2026-10-22 Origin: Site
Four plans cover most single-seal pump services. The number on the datasheet decides whether the seal runs for years or fails in months.
A mechanical seal lives or dies by what happens inside the seal chamber, not by how the seal is built. The flush plan is the plumbing that sets that environment. Most single-seal services in refineries and chemical plants land on four plans, Plan 11, Plan 13, Plan 21 and Plan 32. They get specified every day. They are not interchangeable.
The trap is treating the plan number like a menu option. Each one only holds up under certain conditions, and the wrong pick quietly cuts seal life from years to months. A pump running dirty slurry on Plan 11 plugs the orifice and cooks the faces. A hot pump on Plan 11 with no cooler does the same thing, just slower.
Here is the fast version before the detail.
Plan | How it works | The condition it fits | Where it fails |
|---|---|---|---|
11 | Recirculation from pump discharge through an orifice into the seal chamber. No cooler, no external hardware. | Clean, cool, non-flashing fluid below about 80 degrees C. Water, light oil, ordinary chemical streams. | Dirty, abrasive, polymerizing or hot fluid. The tiny orifice plugs, then the faces run dry. |
13 | Recirculation from the seal chamber back to pump suction through an orifice. Chamber pressure drops. | Vertical pumps, high suction pressure services, anywhere discharge flush is unwanted. Suppresses vaporization at the faces. | Still needs clean fluid. Dirty product plugs the orifice just as fast as Plan 11. |
21 | Plan 11 with a cooler in the line. Discharge fluid passes a heat exchanger before the faces. | Hot clean service above roughly 80 degrees C. Boiler feed, hot light oil, anything that would overheat the faces. | Fluid still has to be clean. A cooler on dirty fluid just moves the plugging problem upstream. |
32 | External clean fluid, utility water, clean product or condensate, floods the seal chamber from outside. | Abrasive, corrosive, polymerizing or slurry media. The seal never touches the bad fluid. | Dilutes the product and needs a dependable engineered external source. A wall water line is not a design. |
Plan 11 pulls fluid from the pump discharge, sends it through a small orifice and pushes it into the seal chamber. No external hardware, no cooler, just a drilled hole with a restriction. This is the default for clean, cool, non-flashing service. Water, light oil and ordinary chemical streams below about 80 degrees C belong here. The fluid lubricates the faces and holds chamber pressure above the vapor pressure so the fluid does not flash.
It fails the moment the fluid turns dirty, abrasive, polymerizing or too hot. The orifice is tiny. One grain of solids or a film of coke and it plugs. Then the faces run dry and the failure is loud. A high-temperature amine pump kept cooking its seal faces on Plan 11 for months before anyone traced it, the plan never removed heat, it only moved fluid around.
Plan 13 runs the opposite way. Fluid leaves the seal chamber and returns to suction through an orifice. Chamber pressure drops, which holds vaporization down at the faces. This is the answer for vertical pumps, where Plan 11 would trap vapor at the top of the chamber and gas-bind the seal. High suction pressure services use it as well, anywhere the discharge flush is unavailable or unwanted. The fluid still has to be clean. Dirty product through a Plan 13 orifice plugs just as fast.
Plan 21 is Plan 11 with a cooler in the line. Same discharge-to-seal recirculation, except the fluid passes a heat exchanger before it reaches the faces. Hot clean services above 80 degrees C need this. Boiler feed, hot light oil, anything that would overheat the faces and coke the film. The cooler does the work. Without it, Plan 21 is Plan 11 wearing a different tag, and the faces still burn.
Plan 32 throws the process fluid out completely. A clean external source, utility water, clean product or condensate, floods the seal chamber and keeps the bad stuff off the faces. This is the only one of the four that handles abrasive, corrosive, polymerizing or slurry media, the seal never touches the dirty fluid. The cost is real. The clean flush dilutes the product, and the plant has to supply, meter and keep that external source dependable. A water line on the wall is not a Plan 32 design. The source needs engineered flow and pressure or the seal sees contamination anyway.
One thing gets missed often. These four are single-seal plans. Foul, toxic or flammable media that must not reach atmosphere call for a dual seal with a barrier system, Plan 52 or the 53 family. Forcing Plan 32 onto a hazardous service to dodge a dual seal is how sites collect emissions records they never budgeted for.
The orifice size, the flush rate and the cooler duty all have to match the seal manufacturer's minimum. A plan written on the datasheet means nothing if the orifice is wrong or the external source cannot deliver. Specifying the right seal with the wrong plan stays the costliest mistake in pump sealing.
FBU builds pre-set, pressure-tested cartridge mechanical seals for these exact duties. The EDMA, GSMH, GDMH, EDMH and ESMH series fit ANSI B73 centrifugal pumps, Sulzer APP compatible pumps, pulp and paper equipment and general chemical process pumps. Seal selection follows the actual medium and the operating condition, not just the catalogue price, and the flush plan is part of that selection rather than an afterthought.
Is Plan 11 enough for most pumps?
For clean, cool, non-flashing fluid below about 80 degrees C, yes, it is the default and it works. Run it on dirty, hot or polymerizing fluid and the orifice plugs or the faces overheat, which is where Plan 21 or Plan 32 takes over.
When is Plan 21 needed instead of Plan 11?
When the process fluid runs above roughly 80 degrees C and still has to reach the faces cool. Plan 21 is Plan 11 plus a cooler, and the heat exchanger removes what Plan 11 cannot.
Why would anyone use Plan 32 if it dilutes the product?
Because the process fluid is dirty, abrasive, corrosive or prone to polymerization, and the seal would fail fast if it met that fluid. Plan 32 keeps a clean flush between the seal and the bad media. The dilution cost beats the alternative of constant seal failure.
Can Plan 13 run on its own?
Often yes, on vertical pumps and high suction pressure services where the chamber needs to drain back to suction and stay under vapor pressure. It still needs clean fluid. Many vertical pumps run Plan 13 alone, and some add Plan 11 as Plan 14 when both venting and positive flow are required.
