Flowserve Seal Support Reservoir - Manual (Page 4)

API Plan 52/ANSI Plan 7252 for dual unpressurized seals
An API Plan 52/ANSI Plan 7352 is an unpressurized dual seal system which
is used in services where no leakage to atmosphere is tolerated. The system
consists of dual mechanical seals with a buffer fluid between the seals. The
buffer fluid is contained in the seal pot which is vented to a flare, thus maintaining
the buffer fluid pressure close to atmosphere. Primary (inboard) seal leakage will
be product leakage into the buffer fluid. There will always be some leakage.
An API Plan 52/ANSI Plan 7352, Figure 2, works best with clean, non-polymeriz-
ing products which have a vapor pressure higher than the buffer fluid pressure.
These products will flash in the supply tank and the vapor can escape to the vent
system. If the product has a vapor pressure lower than the buffer fluid or supply
tank pressure, the leakage will remain a liquid and will cause the barrier fluid level
to rise.
Should excessive primary (inboard) seal leakage not be detected early, the
heavier process fluid will displace the buffer fluid and can result in increased
seal wear.
4
Dual Unpressurized Seal with Induced Circulation
Through Supply Tank with Cooling Coils Figure 2
API Plan 52/ANSI Plan 7352
4 feet (1.2 m)
maximum
1.5 - 2 feet
(0.45 -0.6 m)
minimum
Orifice
option
Bypass line
from pump
discharge
Supply
tank
assembly
Level switch (high)
Level switch (low)
Pressure
switch
(high)
Pressure
indicator
Cooling
coils
Drain
normally
closed
To flare
or vapor
recovery