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Planning the installation Page 2 of 8 Chapter 3

VF03de05a.doc Subject to technical alterations Sterling SIHI 2003

3.1.1 Circulating liquid operation

This method of operation is recommended for:

Service liquids that due to their properties must

neither leave the process circuit nor come into

contact with the cooling liquid (e.g. when using

oil, alkali or acid as service liquid). Waste water systems that must not be

contaminated by the service liquid or by the gas

dissolved in it etc.

The service liquid B consists of circulating liquid

U (B = U) that is cooled in the heat exchanger to therequired operating temperature. The heat exchanger

must be selected so that it is able to extract

completely the heat generated in the service liquid

both by the effects of the motor and by the latent

heat arising from any gas condensation.

ATTENTION

In case of this operating method the inner liquidreturn is not possible. Therefore the adjusting screw

must not be turned out according to the paragraph

3.2.8.

The liquid pump shown in the circulating liquid line is

necessary if the vacuum pump runs without a

significant pressure difference between suction and

discharge branch or, if the flow resistance of the heat

exchanger exceeds approx. 0.2 bar.The heat exchanger can be omitted if the vacuum

pump runs for only few minutes and the liquid can

cool down to around ambient temperature before the

next start-up.

3.1.2 Combined liquid operation

The service liquid B consists of make-up liquid F and

circulating liquid U (B = F + U). The circulating liquidU flows either through the circulating liquid line or it

is taken directly from the surge chamber during the

inner liquid return (assembly according to 3.2.8). A

liquid flow equal in quantity to the make up liquid F

supplied, leaves the separator as drain liquid A

through the liquid drain uA. The make up liquid shall

have only slight overpressure (max. 0.1 bar or max.

0.1 bar exceeding the compression pressure).

3.1.2.1 Lay-outThis method of operation has a simple lay-out,

requires little space and has a reduced make-up

water consumption.

The circulating liquid line is not necessary if the

adjusting screw for the inner liquid return has been

removed according to the section 3.2.8. If theseparate discharge of gas and liquid is not required

the top mounted separator can be omitted. A pipe

discharging into an outlet (gully) is sufficient. The line

for cavitation protection, is led from the connection

uc and must be connected to this pipework.

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3.1.2.2 Temperature regulation

In combined liquid operation the make-up liquid flow

is regulated by means of a thermostat. In this way

the required temperature of the service liquid can be

maintained.

3.1.3 Make-up liquid operation

In uses corresponding to Category 1, it is not

permitted to operate the pump using only make up

water in the pump

This method of operation is applicable where

adequate liquid is available and where there is no

need to reuse it as service liquid.

The make-up liquid method of operation is

recommended also in those cases where the

temperature increase in the vacuum pump is low,

e.g. when handling liquids with a low specific heat. In

this case the inner liquid return is not reasonable so

that the adjusting screw should not be turned out

according to the section 3.2.8.

If the separate discharge of gas and liquid is not

required the top mounted separator can be omitted.

A pipe discharging into an outlet (gully) is sufficient.

The line for cavitation protection, is led from the

connection uc and must be connected to this

pipework. The service liquid B consists of make-up

liquid F (B = F). Its pressure should not exceed 0 bar

(atmospheric pressure) at the manometer vacuum

gauge.

If the pressure in the make-up liquid line varies

considerably so that a temporary overpressure of

about 0.1 bar at the manometer vacuum gauge is

likely to be exceeded, a pressure reducing valve

must be installed or the make-up liquid must be

diverted into a tank with float valve (see fig. below).

The liquid level in the tank from which the vacuum

pump is supplied with service liquid must be at shaft

level.

For compressor operation the make-up liquid must

be supplied at discharge pressure.

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3.2 Pump, pipework connections

ATTENTION

Take note of the arrows indicating flow direction.

The nominal diameters of the pipework must not

be smaller than the nominal diameters of the

corresponding pump branches.

All pipework must be cleaned prior to installation

of the pump.

The pipework must be supported in order to

avoid damage to pump components (danger ofbreaking the pump components).

The suction, discharge and service liquid lines

must be as short as possible and their cross

section must be at least as large as the

corresponding pump connections. For long

lengths of pipework larger cross sections are

required.

LEH. 350 / 450, LEH. 600 / 800 / 900:

The service liquid line can be connected to the

second connection uB as well. This can be made

alternatively but also additionally. If both connections

are used, it must be ensured that the pressures and

liquid flows are the same size.

As from construction size LEH.1200 / 1500 / 1800:

The connections uB must be used on both sides.

3.2.1 Position of the pump

The pump must be installed horizontally; the suctionbranch then points vertically upwards.

3.2.2 Protection against cavitation

Long operating periods under cavitation result in

damage to the material of the pump and failure of

the liquid ring vacuum pump.

To ensure cavitation-free operation the pump must

continuously be supplied with a minimum quantity of

non condensable (inert) gas.

Cavitation occurs if the pumping medium consistsmainly of vapour that condenses during

compression. In order to prevent this, the

connections uc at the pump and at the separator

must be connected by pipework or by a hose. This

enables the vacuum pump to draw non-condensable

(inert) gas from the separator, if the suction pressure

is 40 mbar or lower. This type of connection serves

mainly to protect the pump during start-up if the

suction side is closed (i.e. not effective protectionduring continuous operation with suction side

closed).

If the liquid ring vacuum pump is run at a suction

pressure close to the vapour pressure of the service

liquid, cavitation can also occur. In order to prevent

cavitation at this operating point, the pump must be

vented with non-condensable (inert) gas at the

connection um.

Cavitation does not occur, if the vacuum pump

operates in combination with a gas ejector.

Independent of the service liquid used, the

suction pressure p1,min must not be allowed to

fall below the preset limit. An inert (non

condensable) gas must then be fed on the

suction side.

The smallest permitted suction pressure p1,min

is 20 mbar higher than the vapour pressure of the

service liquid.

If pure vapour is pumped with the liquid ring

vacuum pump, then on the suction side an inert

gas must always be supplied.

3.2.3 Suction line

A non-return valve should be installed in the suctionline. For that purpose the SIHI non-return valves,

type XCk, have proved to be good because of their

low pressure loss.

The venting of the pump, for example during

starting-up and stopping, is possible by means of a

vent cock, which must be installed at the

connection ul um1 resp.

If the pump is started or stopped with a closed shut-

off component, e.g. valve in the suction line,

cavitation will occur. This can be avoided by

adopting cavitation protection measures (see 3.2.2).

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3.2.4 Discharge line

The valve (1) must not be closed during pump start-

up.

3.2.5 Operation with minimal pressure

difference

If a pump is run for a long period without a significant

pressure difference (less than 0.2 bar), e.g. toevacuate a large tank, an orifice plate must be

installed in the suction line.

3.2.6 Shaft seal

Mechanical seals or gland packing are used to seal

the shaft. In the as delivered pump, seal flushing is

by liquid from the interior of the pump.

To change the pump to flushing / sealing with an

external liquid, please contact the manufacturer.

3.2.7 Dirt drain

If any fine-grained dirt went along with the pumped

gas or the service liquid might reach the pump, it can

be washed out by liquid through the connection use

during the operation in order to avoid any corrosion.

In case of strong dirt sediment the dirt drain can be

operated continuously.

In order to safely wash out the dirt particles the

suction pressure should not be lower than approx.

300 mbar. However it must be observed that the

pump is nearly completely drained through this

connection during standstill. Therefore the drain line

must be closed before putting out of operation or the

pump must be refilled up to the shaft height before

putting into operation.

3.2.8 Inner liquid return

In the casing the pump has a mounted line for the

liquid return from the surge chamber up to the

service liquid chamber. During delivery this line is

closed by an adjusting screw (grub screw). Itbecomes accessible after turning out the locking

screw on the connection uiF. The inner liquid return

enables a combined liquid operation with a low

expenditure of technical devices. The make-up liquid

must be fed with slight overpressure. The make-up

liquid flow can be regulated by the pressure.

LEH. 600-900

LEH. 1200-1800

LEH. 2200 / 3000

LEH. 3600 / 4400

LEH. 350 / 450

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3.3 Electrical connections

For the drive motor a mains connection is required

that complies with the regulations valid at site.

The rules and instructions prescribed by the local

public utilities regarding precautions against

explosion must be observed. The motor protectionswitch or the excess current trip must be adjusted to

the rated current of the motor.

3.4. Accessories

The following accessories are available for liquid ring

vacuum pumps:

Motor protection switch to control the power

absorption of the motor

Soft starter

Liquid separator Gas ejector

Heat exchanger

Required connection pipework

Fittings for the thermostatic control of the service

liquid temperature

Ball type non-return valve

Drain valve

Safety valve

Liquid discharge trap

3.4.1 Motor protection switch

The motor protection switch controls the power

absorption of the drive motor. If the rated current is

exceeded the motor is switched off automatically.

3.4.2 Soft starter

A soft starter can be used to start-up the pump. Slow

acceleration of the pump is preferable both for the

pump/package and for the power system.

3.4.3 Liquid separator

A part of the service liquid leaves the pump together

with the compressed gas. In the liquid separator the

gas and liquid are separated.

The following types of liquid separators are available:

top mounted liquid separator

upright liquid separator

3.4.4 Gas ejector

Sterling SIHI gas ejectors complement Sterling SIHI

liquid ring vacuum pumps.

Detailed information is available from the operating

instructions for gas ejectors.

3.5. Compressor operation

If the operational limits (see chapter 9) are observed,

this pumps can also be used as compressors.

For compressor operation a pressure liquid

separator XBd should be used and be placed in such

a way alongside the liquid ring compressor that the

liquid drain uA is at shaft level. A safety valve, set in

accordance with the operating conditions, must be

connected to the connection ub of the separator. A

liquid discharge trap XUk must be provided for thedrain liquid.

For this application there are three different methods

of operation:

- Circulating liquid operation

- Combined liquid operation

- Make-up liquid operation

If the evacuated gases or vapours are inflammable

or injurious to health, a gas tight take-off must be

installed. In addition leakage tests must be carriedout at regular intervals. This is also required after

repair work.

ATTENTION

In case of compressor operation > 0.5 bar the EU

Pressure Equipment Directive must also be

observed.

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3.6 V Belt Operation

The preferred method of drive for the load on both

the pump shaft and on its bearings is direct drive. In

case of large vacuum pumps it is recommendable to

use a gearing between motor and pump. If a V-belt

drive is to be used, the motor should be arranged asfollows:

Pump with clockwise rotating shaft (fig. 3.6):

Motor adjacent to and on the right side of the

pump

Pump with anticlockwise rotating shaft:

Motor adjacent to and on the left side of the pump

fig. 3.6 Pump with clockwise rotating shaft

ATTENTION

The minimum permitted diameter of the pulley is set

out in chapter 9.3.

In Ex- areas, electrically conducting pulleys must be

used (< 106). The halves of the sheave must be

electrically connected to ensure that they are at the

same potential.

3.7 Explosion protection

In accordance with the Directive 94/9/EG, all

components of a package for use in explosive areas

must comply with the required equipment category.

In this connection it is important to distinguish

between the location of the pump and the internal

environment of the pump.

3.7.1 Location

Pump location corresponds to Category 2.

3.7.2 Internal environment of the pump

Requirements:

If it is required that the internal parts of the pump

conform to Category 2, then the following additional

requirements must be considered at the planning

stage of the installation.

Category 1 for the pump internals:

For applications requiring Category 1, the operating

instructions Ex 1G/2G must, in addition, be adhered

to.

Category 2 for the pump internals:

Explosion protection in the working chamber of the

liquid ring vacuum pump is assured by prevention of

any effective ignition source. This is made possible

by ensuring that in all operating conditions (at start

up, shut down as well as when operating) a sufficient

quantity of liquid is in the pump. For conformity with Category 2 for the pump

internals, the level of the liquid in the pump on

start up and the liquid inlet during operation, must

be monitored.

When a safety control is activated, the vacuum

pump must automatically switch off.

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Technical Execution:

To guarantee Category 2 for the internals of the liquid ring vacuum pump, Sterling SIHI suggests the following

layout:

N1 = Process gas

N2 = Gas out

A = Overflow

F = Make-up liquid

K = Cooling liquid

c = Cavitation protection

e = Draining

Flow chart: Vacuum pump system with alternative safety devices

Package with liquid separator unit with coupled cavitation protection pipework and with a backflow

prevention ball valve in the suction line.

Measuring equipment:

LS1 Liquid level in the vacuum pump

or

LS2 Liquid level in the adjacent liquid separator.

FS1 Liquid flow in the service liquid line

or

TS1 Temperature in the pressure chamber of the pump casing or in the pressure line directly behind

the discharge orifice of the pump.

The measurement positions LS1 and LS2 should be adjusted so as to be on the same level as the shaft of the

liquid ring vacuum pump. For LS1 the connection um1 resp. um (see dimensions table) can be used.If a check valve is installed in the service liquid line from the liquid separator to the pump, it must be ensured that

during start up as well as during operation, that the valve remains open.

Monitoring of the pressure in the pressure line PS2 is recommended if, because of the system design, the

permitted compression pressure (see Chapter 9) is likely to be exceeded.

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