Flowserve Seal Support Reservoir - Manual (Page 5)

5
Buffer/Barrier Fluid Selection
The following should be considered when selecting a barrier/buffer fluid:
• Compatibility of the fluid with the process pumpage being sealed so as not to
react with or to form gels or sludge when the fluids are intermixed.
• Compatibility of the fluid with the metallurgy, elastomers and other
materials of the seal/flush system construction.
For an API Plan 53A/ANSI Plan 7353A pressurized barrier fluid system where
the method of pressurization is a gas blanket, special attention must be given to
the application conditions and barrier fluid selection. Gas solubility in the barrier
fluid increases with the rising temperature and pressure. As pressure is relieved
or temperatures cool, the gas is released from the solution and may result in
foaming and loss of circulation of the barrier fluid. This problem is normally seen
where higher viscosity barrier fluids, such as lube oils, are used at pressures
above 150 psig (10.3 bar). Synthetic barrier fluids offer greater compatibility and
wider operating ranges where traditional fluids have problems.
The viscosity of the barrier/buffer fluid should be checked over the entire
operating temperature range with special attention being given to start-up
conditions. The viscosity should be less than 500 cst at the minimum
operating temperature.
1. For services above 50°F (10°C), hydrocarbon barrier/buffer fluids having a
viscosity below 100 cst at 100°F (37.8°C) and between 1 and 10 cst at
212°F have demonstrated proper operating climate.
2. For services below 50°F (10°C), hydrocarbon barrier/buffer fluids having a
viscosity between 5 and 40 cst at 100°F (37.8°C) and between 1 and 10 cst
have demonstrated proper operating characteristics.
3. For aqueous streams, mixtures of water and ethylene glycol or propylene
glycol are usually adequate. Commercially available automotive antifreeze
should never be used. The additives in antifreeze tend to plate out (leave a
residue) on seal parts and cause failure as a result of gel formation.
Note: Ethylene glycol may be considered a hazardous material and/or
hazardous waste when used as a barrier fluid.
4. The fluid should not freeze at the minimum site ambient temperature.