EN – 9
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.
Anti-noise
Anti-suckback
and tightness at
stopping
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.
Gas ballast
When condensable vapors are being
pumped, gas is compressed beyond
its saturated vapor pressure in
the «compression» phase and
can condense, impairing pump
performance and life.
The gas ballast can be used to inject
a certain quantity of air (inert or dry
gas) into the last stage of the pump
during the «compression» phase so
that the partial pressure of the pumped gas is less than its saturated vapor pressure
at the temperature of the pump. Condensation is therefore impossible if this limit is
not reached.The maximum admissible vapor pressure is obtained at pump inlet for this
value.
At the end of «compression», the pressure in the exhaust chamber is greater than
atmospheric pressure. An anti-suckback device (valve + spring) prevents the gases and
oil from being draw back into the inlet.
The saturated vapor pressure of a body is higher when the system is hot than when
it is cold; therefore, the pump must reach operating temperature before pumping
condensable vapors.
In.
COMPRESSION
air
Exh.
EN
Intr
oduction
