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API Plan 74


Externally pressurised barrier gas supplied through a gas control system to a dual seal arrangement. An inert gas is used as a barrier gas.


1. Media leakage to atmosphere is eliminated.

2. Obtain very high reliability, as solids or other materials, which can lead to premature seal failure cannot enter the seal faces.


This plan is intended to be used for dual pressurised non-contacting gas seals.

1. Used in services which are not hot (within elastomer temperature limit) but which may contain toxic or hazardous material whose leakage to atmosphere can not be tolerated.

2. In case of solids or other material present in sealing media.

3. Where process contamination is allowed but process liquid leakage to atmosphere is not allowed.


1. Always ensure barrier gas pressure is higher than seal chamber pressure.

2. Causes media contamination due to high-pressure nitrogen entering the pump.

3. Pressure control valve should be set at least 1.7 bar greater than the seal chamber pressure.

4. Carefully consider the reliability of barrier pressure source, if central pressure issued.

5. Always check filter for any possible blockage.

6. Do not use for sticking or polymerizing media.