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Lubrication / Anti-noise / Anti-suckback
Lubrication
The pump is equipped with a lubrication system which regulates the oil flow rate
required in the vacuum pump. In addition this system also ensures the gasing of the
lubrication oil and therefore the low noise level of the pump at ultimate pressure
(without gas introduction).
When the pump begins to operate, the cooled oil (from the bottom of the oil
casing) is pulled in by the oil pump (2) and drawn in through the oil inlet tube (3).
It is then agitated by a venturi tube (4) and forced into the chamber (6) which is
adjusted by the diaphragm spring system (7).
The discharge pressure of the oil pump (2) lifts the diaphragm off its seats (8)
allowing oil to reach the functional block via the oil injection line (through seats)
(8). An orifice (9) equipped with a jet located in the oil lubrication system allows
trapped gases to be expelled out of the chamber (6).
Cl series pumps are equipped with an
automobile type oil filter, which traps
particles from the oil pumps exhaust.
Due to its construction, its life time is
reduced when pumping on corrosive
products in large quantities. In this case,
an auxiliary oil filtering system is
recommended
(see page
73)
and the
filter is replaced by a stainless steel
short-circuit stopper.
Anti-noise
Parallel to the oil flow, there is a small orifice in the venturi tube (5), which reduces
the noise level at ultimate pressure. Because of the negative pressure created at the
end of the venturi tube (5), gases are entrained into the moving layers of oil
dampening pump noise, allowing the fluid to become more compressible.
The added gases will affect the ultimate pressure, therefore, a compromise between
sound level and ultimate pressure has to be reached as follows:
- Tightening down air intake tube (5) decreases the oil flowrate at the intake of the
oil pump (2) and increases the amount of gas mixture in the oil. The sound level
decreases but the ultimate pressure increases.
- Unscrewing tube (5) increases the oil flowrate at the intake of the oil pump (2)
and decreases the amount of air mixture with the oil. The sound level increases but
the ultimate pressure decreases.
This adjustment can be performed via the oil fill port while the pump is in operation
at ultimate pressure.(a plug is designed for this purpose on the oil case single stage
pump).
Anti-suckback
When the pump is stopped or the power is turned off, the anti-suckback device (6),
(7) and (8) isolates the functional block of the pump against air or oil returning to
the chamber being evacuated..
When the pump stops, the discharge pressure of the oil pump (2) drops rapidly
through the jet (9). Diaphragm (7) under pressure from spring and the difference of
pressure is forced againts its seat (8) thus closing off the injection line through the
seat (8).
The seal is also ensured by flush-mounted o-rings between the faces of the functional
parts (stators, flanges, housing...) and by spring loaded check valves in the
discharge ports.
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