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–

dry,

–

dust free and

–

vibration free.

For commissioning after conservation:

●

Make sure that all remains of adhesive tape are removed from the
ports

●

Commission the vacuum pump as described in the chapter Installa-
tion and Commissioning (

page 5)

Installation and
Commissioning

Installation Prerequisites

CAUTION

In case of non-compliance with the installation prerequisites, partic-
ularly in case of insufficient cooling:

Risk of damage or destruction of the vacuum pump and adjoining
plant components!

Risk of injury!

The installation prerequisites must be complied with.

●

Make sure that the integration of the vacuum pump is carried out
such that the essential safety requirements of the Machine Direc-
tive 2006/42/EC are complied with (in the responsibility of the de-
signer of the machinery into which the vacuum pump is to be
incorporated;

page 16: note in the EC-Declaration of Confor-

mity)

Ancillary Conditions

The chapter Principle of Operation (

page 3) describes the basic

function of a vacuum pump. This description assumes, that the liquid
ring stays liquid all the time.

Actually the condition of both the operating liquid and the conveyed
media depend on the physical conditions pressure and temperature.

At very low pressures and sufficiently high temperatures the operating
liquid can locally transfer into the vapour phase, creating bubbles
within the operating liquid. As the pressure rises towards the outlet
port (e) the bubbles collapse. This process is called cavitation. In case of
bubbles that have been located on surfaces the operating liquid cannot
intrude the cavity left by the bubble equally from all directions. Instead
the inflowing liquid hits the surface with high speed. This causes ero-
sion, which can destroy the vacuum pump rapidly. Also the formation
of bubbles deteriorates the pump performance. Cavitation is clearly au-
dible by its rumbling noise.

For a trouble-free operation the vacuum pump shall be filled with op-
erating liquid approx. up to the shaft centre before the pump is
switched on. A low liquid level deteriorates the pump performance.
A dry start causes failure of the mechanical seal on the shaft of the
vacuum pump. A start with a completely flooded housing damages the
blades of the impeller.

Once the vacuum pump is running operating liquid can be supplied.
Excess operating liquid will then be thrown out through the outlet. The
pressure of the supplied operating liquid shall not exceed the outlet
pressure of the vacuum pump by more than 0.1 bar, otherwise the
pump performance will deteriorate. The best solution is a reservoir un-
der atmospheric pressure from which the vacuum pump sucks in oper-
ating liquid automatically.

The pressure control and the operating liquid supply system of a
vacuum pump must therefore fulfill the following tasks:

–

limit the operating pressure to a value at which no cavitation will
occur

–

control the level in the operating liquid separator and if appropri-
ate, cool the operating liquid to a temperature at which no cavita-
tion will occur

Operating the vacuum pump close to its ultimate pressure requires
large quantities of cool operating liquid. In order to avoid cavitation it
is usually more prudent to limit the minimum working pressure.

The pressure on the suction side of the vacuum pump must not fall be-
low the minimum allowed operating pressure. Therefore it is not al-
lowed to use a pressure control the actuator of which would throttle or
even close the suction line.

The most effective measure to limit the inlet pressure is the use of a
vacuum relief valve.

The vacuum relief valve can either be installed in the suction line or on
the housing of the vacuum pump. The gas supply line of the vacuum
relief valve is usually connected to the liquid separator. Alternatively
ambient air can be used to limit the vacuum.

Feeding ambient air cools, acts against condensation or solution of pro-
cess gas in the operating liquid and therefore reduces the risk of cavita-
tion, however, it mixes the process gas with ambient air, i.e. with
oxygen, which is possibly not desired. Drawing air from the liquid sep-
arator avoids mixing with ambient air, however, this air is usually
warmer, promotes the accumulation of condensed or solved process
gas in the operating liquid, hence increasing the risk of cavitation. If
the primary task is to suck vapours, a non-condensing gas should be
selected for the admixing.

Layout Proposals

The working principle of the liquid ring is dependent upon a continu-
ous supply of clean operating liquid, which is normally water. The op-
erating liquid enters the Vacuum pump/ Compressor/ Vacuum and
pressure pump/ Blower through a connection B on the housing and is
discharged from the Vacuum pump/ Compressor/ Vacuum and
pressure pump/ Blower along with the process gas.

For the layout of an operating fluid supply system there are basically
three different models:

–

Once through cooling / no recovery

–

partial recovery

–

closed loop / total recovery

All of these arrangements have four basic elements:

–

Source of the operating liquid (from the water main or reservoir)

–

Regulating device to control flow of liquid