Edwards ATEX 1 EHR, Instruction Manual

Page: 12 / 50

A750-04-880 Issue F
Page 4 © Edwards Limited 2012. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.
Introduction
The T4 temperature classification is achieved by limiting the temperature of the sealing liquid ring and of the seals
flush liquid (supplied to each of the mechanical seals) to 70
o
C. The maximum temperature rise which can occur in
the seals flush liquid is 30
o
C (assuming that a non-flashing hydrocarbon liquid is used: see Table 1 ). Therefore, the
maximum external temperature of the seals is 100
o
C, which is within the T4 classification requirements.
The maximum operating temperature of the pump is determined by:

The temperature of the sealing liquid supply.

The temperature rise of the sealing liquid in the pump, due to power absorbed by the liquid ring to effect gas
compression.

The temperature rise of the sealing liquid in the pump, due to the condensation of vapours which enter the
pump.

The temperature rise in the seals flush liquid to the mechanical seals, due to friction between the stationary
and rotary parts of the seals.
If you use a total recirculation sealing liquid supply system (see Section 3.5 ), your cooler must be suitable for the
temperature rises that will occur.
Conservative estimates of the temperature rise for different seals flush liquids are shown in Table 1 (see below). Note
that mineral oil is included in Table 1 for comparison purposes only; you cannot use mineral oil as the seals flush
liquid, due to the resulting high temperature rise.
Table 1 - Temperature rises in seals flush liquids
The liquid ring pumps are virtually isothermal machines and, for applications that use water as the sealing liquid, the
temperature rise across the pump is approximately 5
o
C. The temperature rise is directly proportional to the specific
heat of the sealing liquid; for a liquid which has a specific heat which is half that of water, the temperature rise will
be approximately 10
o
C.
With the T4 temperature classification, limiting the sealing liquid ring to a maximum temperature of 70
o
C and
limiting the temperature of the gas at the pump inlet to 70
o
C allows for a temperature rise of 38
o
C in the sealing
liquid; this will never occur, provided that the sealing liquid supply is maintained.
On ATEX Category 1 pumps with external seals flush supplies, you must configure your system so that the seals flush
supplies cannot be interrupted during pump operation (refer to
Section 3.5 ):

You must fit flow switches in the seals flush pipelines of all systems.

You must fit either of the following:

If you use a sealing liquid reservoir to provide the seals flush supplies, fit a level switch to the reservoir.

If you do not use a sealing liquid reservoir to provide the seals flush supplies, fit a pressure switch to the
seals flush manifold.
On ATEX Category 2 pumps with external seals flush supplies, you must configure your system so that the seals flush
supplies cannot be interrupted during pump operation (refer to
Section 3.5 ):

You must fit flow switches in the seals flush pipelines of all systems.

If you use a sealing liquid reservoir to provide the seals flush supplies, you may also fit an optional level
switch to the reservoir.
Liquid
Maximum temperature
rise *
Water/flashing hydrocarbons 20
o
C
Non-flashing hydrocarbons 30
o
C
Mineral oil † 70
o
C
* With maximum rotation speed of 3600 r min
-1
.
† You cannot use mineral oil as seals flush liquid!