BUSCH COBRA DS 0160 G Installation And Maintenance Instructions Manual Download Page 10

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Principle of DP vacuum pumps
The COBRA NS screw vacuum pumps work by the principle of spiral
pumps. Two parallel screws (8) rotate in opposite directions in the
pump body. Entering gases are trapped between the flights of the
screws and the pump body. The gases are conveyed by the rotation of
the screws to the exhaust, where they are discharged.

Principle of MB vacuum pumps
The WY Roots vacuum pumps operate according to the approved
principle of the Roots type machine. Operation is both simple and
effective. Two lobe rotors (1) with identical profiles rotate in opposition
directions within a casing. As they rotate, gas is drawn into the space
between each lobe rotor and the casing (2) where it is trapped and by
the rotation pushed out into the discharge. This action is repeated
twice for each revolution of each lobe rotor and therefore four times
for each revolution of the drive shaft. There is no mechanical contact
between rotors and cylinder. So no oil lubrication is required. The drive
motor of roots pump is a water cooled canned motor.

Gas flow checks

A pressure switch PS at the inlet flange (except for DS 0080, 0160,
1000, 2000 G) monitors the inlet pressure. The MB vacuum pump will
start when the pressure reaches 15 mbar (for DS 0700) and 10 mbar
(for DS 1000, 2000 G). If the pressure does not go down, the DP
vacuum pump stops.

A pressure sensor PRV at the discharge monitors the discharge
pressure. If the pressure reaches more than the limit value (preset at
the factory: 0.2 bar), the purge cycle starts.

Oil circuit

Since the complete operating principle works without contact, no oil
circuit is needed in the work area.

Cooling

The vacuum pump is cooled by

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the filling of cooling water inside the water chambers (6) of cylin-
der and end plate of cylinder B-side. An indirect circuit is made
with a water pump mounted at the motor endplate. The flow of
the cooling water is controlled by a thermostatic valve V1 with a
temperature sensor TS 2. The adjustment of the valve varies the
operating temperature between approximately 50°C (minimum)
and 90°C (maximum) and must be set to suit your operating con-
ditions.
We recommend to use a high valve setting to prevent
resublimation in the vacuum pump.

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a direct cooling water circuit in the motors and the DP transmission
casing. The flow regulating valve CWR 2 of cooling water is preset
on 2 l/min at the factory. The water cools in the DP and MB
pumps motors and the drive/ pump transmission DP system.

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a direct cooling water circuit in the rear bearing (for exceptionnally
cool running in option).

CAUTION

The COBRA DS 0080-2000 G vacuum pumps are generally
dispatched without oil and cooling liquid, without cooling water.
Before vacuum pump first startup, control the oil level and the
cooling liquid level. Operation without these coolants can result in
damage to the vacuum pump.

Nitrogen system

The nitrogen system can be used for diverse functions:

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nitrogen is used as dilution gas. It is injected inside the cylinder on
two different places. Nitrogen flow DGF injected in the middle hole
is preset at 2 l/min and can be adjusted with valve DGR 1, depend-
ing on the application. Nitrogen flow injected in the hole on cylin-
der endplate side is preset at 10 l/min and can be adjusted with
valve DGR 2, depending on the application. When flow is too low
a warning then an alarm signal is generated by flowmeter DGF to
the PLC. Status of the pump depends on the alarm function set by
user (factory setting: None, pump continues running with an
alarm). Dilution improves the screws functioning, especially when
sucking corrosive gases.

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the nitrogen is used as sealing gas. The nitrogen is injected
between the transmission and the process gas to achieve good
closeness.

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the nitrogen is used as purge gas. The purge eliminates traces of
gases remaining in the vacuum pump. The vacuum pump purge
cycle is programmed in the control and starts, either after a STOP
operation or after an alarm function.
For a correct purge execution, the shut-off valve at the inlet flange
must be closed. The purge cycle lasts about 30 min. (Programma-
ble time in the basic parameters).

Optional functions/ Use of available
accessories

The relief valve (SV) prevents excessively high pressure in the
expansion tank (EV), relief pressure: 6 bar.

A pressure switch with normally closed contact mounted in the
expansion tank monitors the pressure of the cooling liquid. It must be
connected in such a way that actuation causes the vacuum pump to be
switched off when the pressure exceeds a value of 3 bar.

A temperature sensor PT100 (10) mounted on the cylinder, measures
the temperature inside the cylinder.

A silencer or sound absorber (accessory) at the exhaust reduces the
noise of the pump and collects any condensate.

A leak-protection non-return valve (optional) at the exhaust traps the
condensate in the pump when the pump is switched off.

The LCD controller shows the data of the sensors as follows:

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PRV: overpressure sensor

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OSG1 and OSG2: DP oil level (option)

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TS 1: temperature in the cylinder DP

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MPS1 : DP current, rotation speed and MPS2: MB current, rotation
speed