- Pump systems (reserve/stand-by pumps)
In the shut-down mode – open suction valve, pressure line closed by shut-off
mechanism (non-return valve) – the mechanical seal is under system pressure from the
suction side. Thus for pumps with double mechanical seals,
the buffer fluid pressure must be greater than the
suction-side system pressure in the shut-down mode, too. For reasons specific to the
system or process it can be necessary to have the reserve pump's suction valve closed. In
this case – experience shows that non-return valves rarely close really tightly
– the mechanical seal is placed under the full discharge pressure of the working
pump. Under these circumstances the axial locking of the stationary seat (stationary seat forms) recommended for double seals (without integral stationary seat locking) is essential.
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If the pumped medium is not allowed to enter the buffer medium, the buffer fluid pressure for the reserve
pump's mechanical seal must be greater than the discharge pressure of the working pump.
A compressor's shut-down internal pressure must be higher than the operating pressure,
especially in the case of refrigerant compressors. Compressors which fulfill this
criterion are equipped with double mechanical seals for
alternating directions of pressure. For a description and illustration of the
mechanical seals see turbo compressors, radial.
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