2. Allow the vacuum pump to warm up prior to process start, with the vacuum flange closed, for ap-
prox. 30 minutes.
Procedure when operating the roots pump in a roots pumping station
The roots pump compresses against one or more backing pumps (e.g. liquid ring pumps).
1. Switch the backing pump on at the mains switch, or on-site, via a protective circuit.
2. Switch the roots pump on at a pressure where the backing pump can withstand the amount of gas
required.
6.3 Adjusting the sealing gas amount
WARNING
Risk of injury from reactive, explosive or other hazardous gas/air mixtures
Uncontrolled gas inlet of air or gases containing oxygen promotes formation of unexpected explosive
gas/air mixtures in the vacuum system. This results in severe injuries.
► Use only inert gases for supplying the sealing gas supply in order to avoid a potential ignition.
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.
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]
Procedure
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. The set quantity of sealing gas influences effective pumping speed and achievable ulti-
mate pressure.
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 inferential meter.
Example for Okta 8000 G with e.g. 50 hPa intake pressure and 8 % sealing gas content
Q
S
= (8000 × 50 × 0.08)/1013 =
Q
S
= 31.6 Nm
3
/h
At discharge pressures > 100 mbar:
Q
S
= (S
th
× (p
V
– ∆p) × A
S
)/p
0
Operation
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