.jpg)
In Piping Plan 53A there is a pressurized external barrier fluid reservoir supplying clean fluid to the barrier fluid seal chamber. The barrier liquid is maintained at a pressure greater than seal chamber pressure.
Barrier liquid is circulated to and from the reservoir by means of an internal circulating device. To maximize barrier liquid circulation, the piping losses should be minimized through the proper selection of pipe size, elimination of fittings, use of large radius bends, and reduction in the length of piping runs.
Piping Plan 53A is used with an Arrangement 3 seal and used in services where no leakage to atmosphere can be tolerated. It may also be selected for applications where the pump may be operated dry or the pump process fluid may be damaging to the seal faces.
A Piping Plan 53A system consists of dual mechanical seals with a barrier liquid between them. The barrier liquid is contained in a reservoir that is pressurized above the seal chamber pressure. Inner seal leakage will be barrier liquid leakage into the product. There will always be some leakage. If seal chamber gauge pressures vary significantly, the inner and outer seal stresses can be reduced by the application of a controlled differential pressure regulator. For specific recommendations on barrier liquid pressurization.
A 3 mm (0.125 in.) orifice is provided in the pressurization gas supply line to limit gas flow into the process in the event of an inner seal failure.
The following comments compare the differences and considerations between all dual pressurized piping plans (Piping Plan 53A, 53B and 53C) and dual unpressurized piping plans (Piping Plan 52). Piping Plan 53 is usually chosen over Piping Plan 52 for dirty, abrasive, or polymerizing products that would either damage the sea} faces or cause problems with the buffer liquid system if Piping Plan 52 were used.
There are two operational features of a Piping Plan 53 that are noteworthy, as follows.
a) The clean barrier liquid provides lubrication to the seal faces, but the barrier liquid that passes across the inner seal faces will enter the pumped process stream. Therefore, the process liquid shall be compatible with the barrier liquid and be able to tolerate a small amount of contamination from the barrier liquid.
b) The reservoir pressure should always exceed the maximum seal chamber pressure by a minimum of 0.14 MPa (1.4 bar) (20 psi). If the reservoir pressure is less than the seal chamber pressure than the normal Ieakage flow direction across the inner seal will be reversed and the seal system will begin to operate like a piping Plan 52. The barrier liquid may become contaminated with the pumped process liquid possibly creating a hazardous barrier liquid and increase the possibility of seal failure.