There are many methods to pressurize the barrier fluid for a dual pressurized mechanical seal. Each method, or piping plan, uses a different mechanism to apply the pressure to the barrier fluid and, as a result, each has its own set of advantages.
One of these methods is American Petroleum Institute (API) Plan 53C. Although not as widely installed as a traditional API Plan 53A system, it does differentiate itself from other methods. API Plan 53C has the ability to change the barrier pressure as the pressure inside the pump changes.