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Plan 02

Plan 02 is a non-circulating flush plan. In Plan 02 the process is not directed into or out of the seal chamber. Seal generated heat is removed by convection and conduction to the process fluid, pump components, and the surrounding environment. Also, some seal chamber designs promote cooling, by mixing of process fluid between the pump cavity and seal chamber. Often, this plan is used in conjunction with API Plan 62 and/or the optional use of a cooling jacket, which will provide some additional cooling. This plan should only be used for services where adequate vapor suppression can be assured, so that vaporization of the process in the seal chamber or at the seal interface does not occur. Plan 02 is often used with a self venting, open seal chamber, i.e. no throat bushing.

Seal Flush Plan 02

Advantages

• No external hardware required.
• Solids are not continually introduced to the seal environment.
• Pump efficiency is not affected, as there is no recirculation of pumped or externally supplied fluid.
• Natural venting occurs with an open chamber throat.   

Disadvantages

• Success of this plan can be difficult to predict, reliance on previous experience with a specific process or pump design is often required.
• If the fluid in the seal chamber vaporizes, the life of the seal will be drastically reduced.
• Fouling of the cooling jacket, if so equipped, over time will reduce its effectiveness, resulting in higher seal chamber temperatures.
• Careful design of impeller/chamber interaction is necessary on low head pumps to prevent air ingression.

General

Low duty, chemical service pumps are often a prime candidate for Plan 02. In these services, it is also advantageous to apply Plan 02 in conjunction with a large (open bore) or taper bore seal chamber. Often, in these services, suspended solids may be included in the process stream. In these cases, devices which encourage seal chamber circulation, while excluding solids from the seal chamber, are available and offered by many OEM and after market suppliers. Applications where these devices have been applied often work well with Plan 02.

Hot, refinery and petrochemical heavy oil services can be successfully sealed with Plan 02. Often, these services congeal or become highly viscous at ambient conditions. This can result in fouling and plugging of the recirculation plans, such as Plan 11, 13, 23 and their derivatives, unless effective temperature control schemes are employed. In these services, Plan 02 offers a relatively simple, cost effective way to obtain reasonable seal life. Only Plans 32 or 54 may be found to provide superior seal life. Use of Plan 02 in hot oil applications normally requires the use of Plan 62, using steam or nitrogen. In most cases, use of a seal chamber cooling jacket is helpful.

Successful use of Plan 02, as with other plans, is dependent on maintaining a lubricating film between the seal faces. This can be accomplished only if vapor formation in the seal chamber can be adequately suppressed. Plan 02, with no forced circulation through the seal chamber, requires thorough venting. This can be accomplished before startup (after pump inventory) or on a continuous basis by means of a self venting seal chamber design. Further, this Plan should be used with caution if the process has entrained gas or other components, which may vaporize easily. This plan is not recommended for vertical pumps.