20
Operation
6
Operation
6.1
Before switching on the pump
Check lubricant levels at both sight glasses and at the oiler as well.
Operate shut-off units in the exhaust line in such a way that they open before or at the
same time as starting the pump.
Protect the pump sufficiently from taking in contaminants by means of suitable precau-
tions (e.g. protective strainer); if necessary, check lubricant regularly or replace at
shorter intervals.
Check pump for visible damage and only start up if it is in the correct condition.
Ensure that the suction chamber is free of foreign particles.
6.2
Switching on the pump
Switch on the Roots pump at the same time as the backing pump or after the backing
pump;
– switch off Roots pump in the event of failure of the backing pump.
The overflow valve is open at the beginning of evacuation in the high pressure range. It
protects the Roots pump from thermal overload. The overflow valve closes starting at a
differential pressure below 7 mbar between the suction side and the compression side.
Operation with
frequency converter (FU)
To protect the pump against overheating, the operation with frequency converter allows
torque-dependant control of the pump speed.
The permissible speed range (20 Hz < n < 75 Hz) must be observed to ensure reliable
bearing lubrication. To protect the pump from damage, an alarm must be triggered and
the pump stopped if it is operated at speeds below 20 Hz for more than 5 minutes.
Adjusting the amount
of sealing gas
Depending on the operating pressure, the empirical value for the supplied sealing gas
amount is between 1% (for a high operating pressure) and 8% (for a lower operating
pressure) of the effective suction capacity. The set quantity of sealing gas influences the
effective suction capacity and the achievable ultimate pressure.
Open gas cylinder 325.
Set a maximum pressure of 2.5 bar at pressure reducer 324.
At dosing valve 315, adjust the desired quantity of sealing gas on the flow meter.
Equation for calculating the sealing gas throughflow
Q
S
= Sealing gas flow under standard conditions [Nm
3
/h]
p = Intake pressure [hPa]
p
0
= Ambient pressure under standard conditions [hPa]
∆
p= Differential pressure max. [hPa]
p
V
= Fore-vacuum pressure [hPa]
A
S
= Proportion of sealing gas in the operating gas flow (0.01
A
S
0.08)
S
th
= Rated suction capacity of the Roots pump [m
3
/h]
CAUTION
Hot surface!
Danger of burns if hot parts are touched. Depending on the operating and ambient con-
ditions, the surface temperature of the pump may rise above 100 °C.
In this case, use suitable finger guards.
S
th
· p · A
S
p
0
Q
S
=
