NOTICE
Property damage from impermissibly high sealing gas pressure
Excessive sealing gas pressure leads to damage to the seals after switching on the vacuum pump.
► Observe the max. permissible sealing gas pressure.
► Reduce the sealing gas pressure to < 1200 hPa.
► Stop the sealing gas supply immediately after switching off the vacuum pump.
Procedure
The set quantity of sealing gas influences effective pumping speed and achievable ultimate pressure.
Depending on the operating pressure, the empirical value for the supplied sealing gas amount is be-
tween 1 % (for a high operating pressure) and 8 % (for a lower operating pressure) of the effective suc-
tion capacity.
Inert gases, mostly nitrogen (N
2
), are used as sealing gas.
1. Open the sealing gas supply on the gas cylinder.
2. Set a max. pressure of 2500 hPa on the pressure reducer.
3. Set the desired quantity of sealing gas on the dosing valve of the flow meter.
Equation for calculating the sealing gas flow:
Q
S
= (S
th
× p × A
S
)/p
0
● 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
= Sealing gas content at the operating gas flow (0.01 ≤ A
S
≤ 0.08)
● S
th
= Rated volume flow rate of the roots pump [m
3
/h]
Example for Okta 500 ATEX with e.g. 50 hPa intake pressure and 8 % sealing gas content
Q
S
= (490 × 50 × 0.08)/1013
Q
S
= 1.93 Nm
3
/h
At discharge pressures > 100 mbar:
Q
S
= (S
th
× (p
V
– ∆p) × A
S
)/p
0
6.5 Checking the power input
DANGER
Risk of injury due to the bearing bursting after overheating
During longer operation with defective bearings, there is a risk of explosion due to hot surfaces if
there is a potentially explosive atmosphere.
► Monitor the motor current of the roots pump so that in the event of a process-independent in-
crease of the motor current > 10 %, the roots pump is switched off.
► As an alternative, perform a vibration measurement at the defined measuring points with the pre-
scribed time intervals.
There are two possible procedures for monitoring the pumping operation:
● Checking the power input
● Vibration monitoring:
(see chapter “Vibration monitoring”, page 36)
pump and the bearing are monitored.
Operation
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