SIST EN 16932-3:2018
(Main)Drain and sewer systems outside buildings - Pumping systems - Part 3: Vacuum systems
Drain and sewer systems outside buildings - Pumping systems - Part 3: Vacuum systems
This European Standard specifies requirements for design, construction and acceptance testing of wastewater pumping systems in drain and sewer systems outside the buildings they are intended to serve. It includes pumping systems in drain and sewer systems that operate essentially under gravity as well as systems using either positive pressure or partial vacuum.
This document is applicable to vacuum drain and sewer systems.
Entwässerungssysteme außerhalb von Gebäuden - Pumpsysteme - Teil 3: Unterdruckentwässerungssysteme
Pumpsystemen in Entwässerungssystemen außerhalb von Gebäuden, zu deren Entwässerung sie dienen, fest. Sie betrifft sowohl Pumpsysteme in Entwässerungssystemen, welche hauptsächlich als Freispiegelsysteme betrieben werden, als auch Systeme, die entweder mit Überdruck oder Unterdruck betrieben werden.
Dieses Dokument gilt für Unterdrucksysteme.
Réseaux d'évacuation et d'assainissement à l'extérieur des bâtiments - Systèmes de pompage - Partie 3 : Systèmes sous vide
La présente norme européenne fournit des prescriptions pour la conception, la construction et les essais d’acceptation des systèmes de pompage des eaux usées dans les réseaux d’évacuation et d’assainissement à l’extérieur des bâtiments qu’ils sont destinés à desservir. Elle couvre les installations de systèmes de pompage dans les réseaux d’évacuation et d’assainissement, principalement les réseaux gravitaires, ainsi que les réseaux utilisant soit une pression positive, soit un vide partiel.
Le présent document s’applique aux réseaux d’évacuation et d’assainissement sous vide.
Sistemi za odvod odpadne vode in kanalizacijo zunaj stavb - Črpalni sistemi - 3. del: Vakuumski sistemi
Ta evropski standard določa zahteve za projektiranje, izdelavo in preskušanje sprejemljivosti črpalnih sistemov odpadnih vod v sistemih za odvod in kanalizacijo zunaj stavb, v katerih so namenjeni za delovanje. Vključuje inštalacije črpalnih sistemov v sistemih za odvod in kanalizacijo, ki delujejo zlasti s pomočjo gravitacije, kot tudi v sistemih, ki uporabljajo pozitivni tlak ali delni vakuum.
Ta dokument se uporablja za sisteme za vakuumski odvod in kanalizacijo.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-junij-2018
1DGRPHãþD
SIST EN 1091:2000
SIST EN 1671:1998
6LVWHPL]DRGYRGRGSDGQHYRGHLQNDQDOL]DFLMR]XQDMVWDYEýUSDOQLVLVWHPL
GHO 9DNXXPVNLVLVWHPL
Drain and sewer systems outside buildings - Pumping systems - Part 3: Vacuum
systems
Entwässerungssysteme außerhalb von Gebäuden - Pumpsysteme - Teil 3:
Unterdruckentwässerungssysteme
Réseaux d'évacuation et d'assainissement à l'extérieur des bâtiments - Systèmes de
pompage - Partie 3 : Systèmes sous vide
Ta slovenski standard je istoveten z: EN 16932-3:2018
ICS:
93.030 Zunanji sistemi za odpadno External sewage systems
vodo
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN 16932-3
EUROPEAN STANDARD
NORME EUROPÉENNE
April 2018
EUROPÄISCHE NORM
ICS 93.030 Supersedes EN 1091:1996, EN 1671:1997
English Version
Drain and sewer systems outside buildings - Pumping
systems - Part 3: Vacuum systems
Réseaux d'évacuation et d'assainissement à l'extérieur Entwässerungssysteme außerhalb von Gebäuden -
des bâtiments - Systèmes de pompage - Partie 3: Pumpsysteme - Teil 3:
Systèmes sous vide Unterdruckentwässerungssysteme
This European Standard was approved by CEN on 22 January 2018.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 16932-3:2018 E
worldwide for CEN national Members.
Contents Page
European foreword . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Symbols and units . 7
5 General . 8
6 Planning vacuum sewer systems . 8
6.1 Basis of design . 8
6.2 Location of collection chambers . 8
6.3 Route and profile of vacuum pipelines. 9
6.4 Hydro pneumatic design of the system . 11
6.5 Vacuum station design . 13
6.5.1 General . 13
6.5.2 Sizing the vacuum vessel for flushing activities . 16
6.6 Power consumption . 17
7 Collection chambers on vacuum sewer systems . 18
7.1 General . 18
7.2 Collection chambers . 18
7.3 Interface valve units . 20
7.4 Explosion safety . 20
7.5 Life of membranes and seals . 21
8 Vacuum pipelines . 21
8.1 Vacuum drain connections . 21
8.2 Branch connections . 21
8.3 Means of isolation . 22
9 Detailed design of vacuum stations . 22
9.1 Selection of type of vacuum pumping station . 22
9.2 Vacuum vessel . 23
9.3 Forwarding equipment . 23
9.4 Non-return valves . 23
9.5 Vacuum pumps . 23
10 Controls, electrical equipment and instrumentation . 25
10.1 Collection chamber controls . 25
10.1.1 Level sensor . 25
10.1.2 Interface valve controller . 25
10.1.3 Monitoring of the interface valve . 26
10.2 Vacuum station control . 26
10.3 Explosion safety . 26
11 Installation . 27
12 Testing and verification . 27
12.1 Collection chambers . 27
12.2 Interface valve units . 27
12.3 Vacuum pipelines . 27
12.4 Commissioning tests . 27
13 Operation and maintenance . 28
13.1 General . 28
13.2 Maintenance . 28
13.3 Operation and maintenance manual . 28
13.4 Power consumption . 29
Annex A (informative) Example of a dimensioning model . 30
Annex B (normative) Testing of vacuum sewer system . 32
B.1 Testing of interface valve unit. 32
B.1.1 Testing requirements. 32
B.1.2 Preliminary checks . 32
B.1.3 Endurance test . 32
B.1.3.1 Test rig description . 32
B.1.3.2 Test procedure . 32
B.1.4 Resistance to blockage test . 33
B.1.5 Submergence test . 33
B.2 Testing of pipelines . 33
B.2.1 Calibrating test equipment . 33
B.2.2 General . 34
B.2.3 Interim testing . 34
B.2.4 Final testing . 34
B.3 Leak testing of collection chambers. 34
B.4 Commissioning tests . 34
B.4.1 General . 34
B.4.2 Noise . 34
B.4.3 Minimum vacuum and vacuum recovery time . 34
B.4.4 Air/water ratio . 35
B.4.5 Operation of vacuum station controls . 35
B.4.6 Replacement times . 35
Bibliography . 36
European foreword
This document (EN 16932-3:2018) has been prepared by Technical Committee CEN/TC 165
“Waste water engineering”, the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by October 2018, and conflicting national standards shall
be withdrawn at the latest by October 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN not be held responsible for identifying any or all such patent rights.
Together with EN 16932-1:2018 and EN 16932-2:2018, this document will supersede EN 1091:1996
and EN 1671:1997.
EN 16932:2018, Drain and sewer systems outside buildings — Pumping systems, contains the following
parts:
— Part 1: General requirements;
— Part 2: Positive pressure systems;
— Part 3: Vacuum systems.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
1 Scope
This European Standard specifies requirements for design, construction and acceptance testing of
wastewater pumping systems in drain and sewer systems outside the buildings they are intended to
serve. It includes pumping systems in drain and sewer systems that operate essentially under gravity as
well as systems using either positive pressure or partial vacuum.
This document is applicable to vacuum drain and sewer systems.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 476, General requirements for components used in drains and sewers
EN 16323:2014, Glossary of wastewater engineering terms
EN 16932-1:2018, Drain and sewer systems outside buildings — Pumping systems — Part 1: General
requirements
EN 16932-2:2018, Drain and sewer systems outside buildings — Pumping systems — Part 2: Positive
pressure systems
EN 16933-2, Drain and sewer systems outside buildings — Design — Part 2: Hydraulic design
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 16323, in EN 16932-1 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
Note 1 to entry: Certain key definitions from EN 16323:2014 have been repeated below for clarity. The
following additional terms used in this document are defined in EN 16323:
collection tank; pumping station;
domestic wastewater; relevant authority;
extraneous flow; rising main;
gradient; runoff;
gravity system; self-cleansing;
infiltration; sewer;
maintenance; sewer system.
non-domestic wastewater;
Note 2 to entry: The following terms used in this standard are defined in EN 16932-1:
collection chamber; level sensor;
controller; lift section;
forwarding pump; profile;
interface valve; pump;
pump unit; vacuum drain;
slope section; vacuum sewer;
vacuum generator; vacuum station,
vacuum pipeline; vacuum vessel.
3.1
air/water ratio (AWR)
ratio of the air volume at standard temperature and pressure to the volume of wastewater
3.2
batch volume
wastewater volume in a collection tank that is removed during an evacuation cycle
3.3
foul wastewater
wastewater comprising domestic wastewater and/or industrial wastewater
[SOURCE: EN 16323:2014, 2.1.2.6]
3.4
interface valve unit
valve and controller in a collection chamber admitting wastewater and air into a vacuum sewer through
a vacuum drain
3.5
length specific population density
total population connected to a vacuum sewer, including its branches, divided by the length of the
vacuum sewer, not including side branches
3.6
surface water
water from precipitation, which has not seeped into the ground and is discharged to the drain or sewer
system directly from the ground or from exterior building surfaces
[SOURCE: EN 16323:2014, 2.1.1.3]
3.7
vacuum recovery time
time taken, after the operation of an interface valve, for the sub-atmospheric pressure at the valve to be
restored to a value sufficient to operate the valve again
3.8
wastewater
water composed of any combination of water discharged from domestic, industrial or commercial
premises, surface run-off and accidentally any sewer infiltration water
[SOURCE: EN 16323:2014, 2.3.10.65]
4 Symbols and units
AWR air/water ratio, dimensionless [-]
D internal diameter of the pipe (bore) in metres [m]
D internal diameter of the pipe (bore) in section i (each section extending from a high point
i
to the next downstream high point), in metres [m]
f maximum start frequency of the vacuum pump per hour [1/h]
A
f maximum start frequency of the forwarding pump per hour [1/h]
W
g
acceleration due to gravity, in metres per second squared [m/s ]
H total head at the pump unit, in metres [m]
p
h
maximum hydrostatic head difference at a lift section, in metres [m]
R
Σh maximum hydrostatic head difference along the connected vacuum pipelines, in metres
R
[m]
J gradient of the slope section in section I, dimensionless [-]
2,i
L length of the lift section, in metres [m]
L length of the slope section, in metres [m]
L length of the lift section at the end of section I, in metres [m]
1,i
L length of the vacuum sewer, in metres [m]
VS
N number of vacuum pumps
A
N number of forwarding pumps
WW
P power consumption of the vacuum pumps, in Watts [W]
A
P power consumption of the forwarding pumps, in Watts [W]
WW
p ambient air pressure, in kilopascals [kPa];
aa
p absolute pressure at the interface valve, in kilopascals [kPa] which is typically a value of
iv
75 kPa
p maximum absolute pressure in the vacuum vessel, in kilopascals [kPa]
max
p
minimum absolute pressure in the vacuum vessel, in kilopascals [kPa]
min
Q maximum air flow at standard temperature and pressure, in litres per second [l/s]
A
Q
capacity of each vacuum pump at standard temperature and pressure, in litres per second
A.p
[l/s]
Q suction capacity of the vacuum pump at the average working pressure of the system, in
A,p,s
litres per second [l/s]
Q design wastewater flow, in litres per second [l/s]
WW
Q
incoming wastewater flow rate, in litres per second [l/s]
WW,in
Q capacity of each forwarding pump, in litres per second [l/s].
WW,p
Q flow of the flushed wastewater, in litres per second [l/s]
WW,fl
R minimum bending radius of a vacuum pipeline, in metres [m]
SF safety factor between 1,2 and 1,5.
t flushing time, in seconds [s];
fl
V minimum volume in the vacuum vessel provided for air, in litres [l]
A
V allowance for the storage volume in the vacuum sewer, which is no more than half of the
AS
volume of those last slope sections of the vacuum sewers, along which the maximum
hydrostatic pressure difference is less than p – p .
max min
V
minimum volume of the vacuum vessel, in litres [l]
min
V internal volume of the vacuum sewer, in litres [l];
vs
V minimum volume provided for wastewater in the vacuum vessel, in litres [l]
W
WWR maximum wastewater ratio in the vacuum sewers, dimensionless [-]
max
z lift height of a lift section, in metres [m]
η efficiency of the vacuum pump units, dimensionless [-]
A
η efficiency of the wastewater forwarding pump units, dimensionless [-]
WW
κ adiabatic coefficient of air = 1,4, dimensionless [-]
A
ρ
density of wastewater, in kilogrammes per cubic metre [kg/m ]
5 General
This European Standard shall be read in conjunction with EN 16932-1. Vacuum systems shall comply
with the requirements of EN 16932-1 as well as the requirements of this European Standard.
6 Planning vacuum sewer systems
6.1 Basis of design
Foul wastewater flow rates into the vacuum system shall be established in accordance with
EN 16933-2. The design peak, the minimum and the 24 h average foul wastewater flow rates shall be
established. Infiltration and other extraneous water flows shall also be taken into account. The designer
shall state the average air and water flows for which the system is designed, the peak flow (litres per
second) used in the design and how the dynamic and static head losses have been calculated.
Where a vacuum system intercepts wastewater from a gravity or pressure system or accepts
wastewater from commercial or industrial sites, the design performance criteria shall be specified,
including the peak flow.
6.2 Location of collection chambers
The decision on whether each property has its own collection chamber or whether properties have
common collection chambers should take account of:
a) the costs;
b) the ease of identifying the-origin of any debris causing a blockage;
c) the levels of the incoming drains; and
d) the available space.
Collection chambers should be located close to the properties served in order to keep the lengths of
drain pipes to the chambers short. They can be located on private property (particularly where each
property is served by an individual collection chamber) or on public ground (e.g. in streets or
footways). However, they shall always be accessible for maintenance by the operator of the vacuum
system unless an isolation valve is provided on the vacuum drain in an accessible location.
The type and costs of chambers shall be considered, e.g. whether they need to have watertight frames
and covers, and whether they need to bear traffic load.
6.3 Route and profile of vacuum pipelines
The route and profile of vacuum drains and sewers should be planned taking account of the following:
a) the numbers and locations of the collection chambers (see 6.2);
b) avoiding up-hill movement of wastewater where possible;
c) minimizing the length of the vacuum pipelines;
d) avoiding obstacles (e.g. ditches, watercourses, major roads, railways) where possible;
e) maintaining a minimum 1:500 downslope gradient in the slope sections. However, this minimum
gradient should be increased where normal construction tolerances (see Clause 11) cannot be
achieved, for example when using trenchless construction methods;
f) short radius bends (R < 3 × DN) should be avoided;
g) limiting the height of each lift section to no more than 1,5 m - a series of smaller lifts is preferable to
a single high lift;
h) limiting the distance between lift sections to no less than 6 metres on vacuum sewers and 1,5 m on
vacuum drains;
i) maintaining self-cleansing conditions in the vacuum pipeline.
Where a wave profile is used the minimum length of a lift section should be (see Formula (1)):
L > 2⋅ z⋅ R (1)
where
L is the length of the lift vsection in metres [m];
R is the minimum bending radius of a vacuum pipeline in metres [m];
z is the height of the lift section in metres [m].
Self cleaning conditions can be maintained by limiting the distances between lift sections to ensure the
flow is deep enough to flush the solids through the slope sections. Where the distance between lift
sections is longer than 150 m the designer should demonstrate how self-cleansing conditions will be
maintained.
Where inspection pipes are provided (see 8.3 and Figure 3) the distance between them is typically not
more than 100 m.
Either a saw-tooth profile or a wave profile can be used. The saw-tooth profile (see Figure 1, upper
diagram) has straight downslope sections and steep lift sections and is typically formed using bend
fittings. The wave profile (see Figure 1, lower diagram) is typically formed by bending flexible pipes.
The saw-tooth profile is easier to install than the wave profile as in the wave profile the high and low
points need to be secured in place. However, the head losses in the wave profile are significantly less
than in the saw-tooth profile.
Examples of the profile of vacuum pipelines are shown in Figures 1 to 3.
Key
1 slope section with minimum 1:500 gradient L length of lift section
2 lift section L length of slope section with minimum 1:500 gradient
distance between low points (L = L + L )
3 inspection pipe (optional) L
1 2
Figure 1 — Examples of vacuum sewer profiles (not to scale) – the upper diagram shows a saw-
tooth profile and the lower diagram a wave profile
Key
1 lift section
2 slope section
Figure 2 —Examples of vacuum sewer profiles for uphill and downhill terrain (not to scale)
Key
1 slope section with minimum 1:500 gradient 3 inspection pipe (optional)
2 lift section L distance between inspection pipes
IP
Figure 3 — Example of a vacuum sewer with sewer inspection pipes (not to scale)
6.4 Hydro pneumatic design of the system
The system design shall achieve a specified minimum partial vacuum of at least 15 kPa at each interface
valve, under no flow as well as under peak flow conditions. Where the base of the collection tank is
more than 1,0 m below the centreline of the interface valve, an accordingly higher minimum partial
vacuum is needed to guarantee reliable evacuation. The head difference between the atmosphere and
the air at the connection of a vacuum drain to a vacuum sewer shall be equal or larger than the level
difference between this connection and the bottom of the connected collection tank plus 5 kPa.
The vacuum recovery time shall not exceed 30 min. The system shall be designed to achieve automatic
restart after mechanical or electrical breakdown.
Explicit hydrodynamic calculation of the flow in vacuum sewers is extremely difficult due to the
complexity of the unsteady multi-phase flow conditions (plug flow, slug flow, mixed air/water flow,
mist) and due to the random nature of the flow pulses.
For this reason, the dimensions of vacuum sewer networks are estimated with the help of models which
take into account the following principles:
a) The sum of the maximum static head differences ( Σh ) along a vacuum sewer should, assuming that
R
the lower ends of lift sections are entirely filled with wastewater and that all slope sections are
entirely filled with air, usually not exceed 5 m.
Where
h is the maximum static head difference of a lift section (see Figure 4)
R
This can be calculated from Formula (2):
h z − D (2)
R
where
z is the lift height in metres [m];
D is the internal diameter of the pipe (bore) in metres [m].
Key
1 slope section with minimum 1:500 gradient z lift height
2 lift section h maximum hydrostatic head of the lift section (h = z-D)
R R
D is the internal diameter of the pipe (bore)
Figure 4 — Example of lift section (not to scale)
Exceptionally somewhat higher static head differences can sometimes be accommodated by installation
of automatic air admission valves that allow air to enter into the vacuum pipeline when the vacuum
pressure drops below an adjusted minimum, in order to prevent all lift sections being simultaneously
filled with wastewater.
NOTE 1 The total headlosses are not necessarily the sum of the pipeline headlosses and the static head
difference as the highest static head will occur at zero flow.
b) In all locations in the network the minimum vacuum required for each interface valve (static head
between the vacuum sewer and the bottom of the collection chamber plus 5 kPa) shall be
maintained.
c) The air/water ratio should be limited to prevent excessive energy consumption.
d) The air/water ratio should be high enough to ensure that the system performs adequately.
=
e) The minimum nominal internal diameter of vacuum drains shall be DN 50 and the minimum
nominal internal diameter of vacuum sewers shall be DN 65.
NOTE 2 National or local regulations or the relevant authority can specify requirements regarding the
minimum diameter of vacuum drains or sewers.
f) In every location in the network, the diameters of the vacuum sewers shall be selected to limit the
head loses. The head losses shall be calculated for a two-phase peak flow. The nominal diameter of
vacuum sewers shall increase with the total equivalent population (the sum of the population for
domestic wastewater and the equivalent population for non-domestic wastewater) connected
upstream and with the mean upstream air/water ratio.
The designer shall provide pressure profiles for the system at rest and at peak flow, depending on the
air/water ratio.
An example of a dimensioning model is set out in Annex A. Other dimensioning models may be included
in a National Annex to this European Standard. The prospective operator of the system or the relevant
authority can specify or approve other dimensioning models.
6.5 Vacuum station design
6.5.1 General
The number and capacity of the duty and duty assist vacuum generators and forwarding pumps shall be
selected for the peak flows of air and wastewater respectively. The minimum volume of the vacuum
vessel shall be calculated taking account of the maximum start frequency of the vacuum generators and
forwarding pumps and the range of operational pressure. The vacuum reservoir capacity shall be
provided by the vacuum vessels and some additional volume available in the connected vacuum sewers.
The maximum air flow Q (at standard temperature and pressure) shall be calculated. This may be
A
calculated from Formula (3):
Q Q ⋅AWR (3)
A WW
where
Q is the maximum air flow at standard temperature and pressure, in litres per second [l/s];
A
Q is the design wastewater flow, in litres per second [l/s];
WW
AWR is the air/water ratio, dimensionless [-].
The capacity and number of the forwarding pumps and of the vacuum pumps should be selected taking
into account the need for redundancy. This may be calculated as follows from Formula (4) and (5):
Q≥−QN/ 1 (4)
( )
WW,p WW WW
and
Q ≥⋅Q SF / N − 1 (5)
( )
Ap, A A
where
Q is the capacity of each forwarding pump, in litres per second [l/s];
WW.p
N is the number of forwarding pumps;
WW
Q is the capacity of each vacuum pump at standard temperature and pressure, in litres per
A.p
=
second [l/s];
N is the number of vacuum pumps;
A
SF is a safety factor between 1,2 and 1,5.
The suction capacity per vacuum pump at the average working pressure shall be calculated. This can be
calculated from Formula (6):
Q ≥ Qp⋅⋅ 2/ p + p (6)
( )
A,p,s A,p aa max min
where
Q suction capacity of the vacuum pump at the average working pressure of the system, in
A,p,s
litres per second [l/s]
p is the ambient air pressure, in kilopascals [kPa];
aa
p is the maximum absolute pressure in the vacuum vessel, in kilopascals [kPa], (see
max
Formula (7), where:
−3
p ≤ p − 0,6 ⋅ ρ ⋅ gh⋅∑ ⋅ 10 (7)
( )
max iv R
where
p is the minimum absolute pressure in the vacuum vessel, in kilopascals [kPa];
min
p is the absolute pressure at the interface valve, in kilopascals [kPa] which is typically a
iv
value of 75 kPa
Σh is the maximum hydrostatic head difference along the connected vacuum pipelines, in
R
metres [m];
ρ
is the density of wastewater, in kilogrammes per cubic metre [kg/m ]; and
g
is the acceleration due to gravity, in metres per second squared [m/s ].
The minimum wastewater volume to be provided in the vacuum vessel shall be calculated. This may be
calculated from Formula (8):
V Q ⋅ 3 600⋅ Q − Q/ Q ⋅⋅f N − 1 (8)
( ) ( ( ) )
W WW,in WW,p WW,in WW,p W WW
where
V is the minimum volume provided for wastewater in the vacuum vessel, in litres [l]
W
f is the maximum start frequency of the forwarding pump per hour. [1/h]; and
W
Q is the incoming wastewater flow rate, in litres per second [l/s].
WW,in
V reaches a maximum when: Q = 0,5 x Q and then Formula (6) can be simplified to
W WW WW,p,
Formula (9):
V=900⋅ Q / f⋅−N 1 (9)
( )
( )
W WW,p W WW
If Q > 2 x Q , which is often the case in small vacuum systems, then Formula (6) can be simplified
WW,p WW
to Formula (10):
V 3 600⋅ Q ⋅−1 Q/ Q/ f ⋅ N − 1 (10)
( )
( ) ( )
W WW WW WW,p W WW
=
=
The required minimum air volume to be provided in the vacuum vessel shall be calculated. This may be
calculated from Formula (11):
V 900⋅ Q ⋅ 0,/5⋅ p + p pp− ⋅ N −⋅1 f (11)
( ) ( ( ) ( ) )
A A,p,s max min max min A A
where
V is the minimum volume in the vacuum vessel provided for air, in litres [l];
A
f is the maximum start frequency of the vacuum pump per hour. [1/h];
A
N
is the number of vacuum pumps.
A
To provide a sufficient vacuum reservoir, the vacuum vessel should not be filled to more than 1/3 with
wastewater.
The required minimum air volume in the vacuum vessel is reduced if the number of vacuum pumps N
A
is increased. However, the number of vacuum pumps N may only be used in this calculation if the
A
pumps are operated in sequence. The required air volume can also be reduced by using variable speed
vacuum pumps. It also depends on the selection of p . It should be noted, that a lower p reduces
min min
V , but increases the power consumption. The required air volume in the vacuum vessel V may also be
A A
reduced by subtracting a portion of the volume in the incoming vacuum sewers V .
AS
The required vessel volume may be calculated from the greater of the results calculated from
Formulae (12) and (13):
VV≥⋅3 (12)
min W
where
V is the minimum volume of the vacuum vessel, in litres [l]; and
min
V is the minimum water volume for wastewater in the vacuum vessel, in litres [l].
W
and
V = V +−VV (13)
min W A AS
where
V is the minimum volume of the vacuum vessel, in litres [l]
min
V is the minimum volume in the vacuum vessel provided for air, in litres [l]
A
V is an allowance for the storage volume in the vacuum sewer, which is no more than half of the
AS
volume of those last slope sections of the vacuum sewers, along which the maximum hydrostatic
pressure difference is less than p – p .
max min
EXAMPLE If the hysteresis is p – p = 10 kPa and a lift section with a maximum hydrostatic head
max min
difference of over 1 m is installed adjacent to the vacuum vessel, then V = 0.
AS
The sizing of the vacuum vessel should also take account of the effects of any operation and
maintenance activities in accordance with the system operator's procedures, for example if waterlogged
(flooded) vacuum pipelines are sometimes flushed with air for up to 3 min at a time. Guidance on sizing
the vacuum vessel to take account of flushing activities can be found in 6.5.2.
=
6.5.2 Sizing the vacuum vessel for flushing activities
The maximum wastewater ratio WWR in the vacuum sewers may be initially estimated, from
max
Formula (14):
WWR ≈∑ 0,/5⋅ D J + L / L (14)
( )
max i 2,,i 1 i VS
where
WWR is the maximum wastewater ratio in the vacuum sewers, dimensionless [-];
max
D is the internal diameter of the pipe (bore) in section i (each section extending from a
i
high point to the next downstream high point), in metres [m];
J is the gradient of the slope section in section i, dimensionless [-];
2,i
L is length of the lift section at the end of section i, in metres [m].
1,i
L is the length of the vacuum sewer, in metres [m].
VS
For a saw-tooth profile with a downslope of 1:500 the following simplified Formula (15) may be used,
whereby the wastewater volume in the short lift sections is neglected:
WWR ≈ 250 ⋅∑ D / L (15)
max VS
For a wave profile with a downslope of 1:500 the following approximation (see Formula (16) may be
used:
WWR ≈∑ 250 ⋅ D + L / L (16)
( )
max 1,i VS
During air flushing the volume of air and wastewater entering the vacuum vessel is approximately equal
to the volume evacuated by the vacuum and forwarding pumps. Thus the incoming flushed wastewater
flow Q in litres per second [l/s] is (see Formula (17)):
ww,fl
Q ≈ WWR ⋅ N −⋅1 Q + Q (17)
( )
WW,fl max A A,p,s WW,p
where
Q is the flow of the flushed wastewater, in litres per second [l/s]
WW,fl
N is the number of vacuum pumps;
A
Q is the suction capacity of each vacuum pump at the average working pressure of the
A,P,s
system, in litres per second [l/s]; and
Q is the capacity of each forwarding pump, in litres per second [l/s].
WW,p
The flushing time t is the time in seconds [s] needed for the entire wastewater in the flushed vacuum
fl
sewer, which has an internal volume V in litres [l], to enter the vacuum vessel (see Formula (18)):
VS
t V ⋅ WWR / Q (18)
fl VS max WW,fl
where
t is the flushing time, in seconds [s] where t ≤ 180 s.
fl fl
V
is the internal volume of the vacuum sewer, in litres [l];
vs
=
Q is the flow of the flushed wastewater, in litres per second [l/s].
WW,fl
In order to avoid the need for too large vacuum vessels, the flushing time t should be limited to 180 s.
fl
If a single flushing cycle should be insufficient, it should be repeated after a break lasting long enough to
permit the forwarding pump to empty the vessel.
The worst case scenario is that the vacuum vessel has been filled to its maximum (V = 1/3 V ) with
w min
wastewater when the flushing begins. To prevent wastewater entering the vacuum pumps, the vessel
should not be more than 2/3 full at the end of the flushing cycle. The volume of the vacuum vessel shall
therefore also comply with the following Formula (19):
V ≥ 1,5⋅ V + t ⋅ Q − N −⋅1 Q (19)
( )
( ( ) )
min ( W fl WW,fl WW WW,P )
where
V is the minimum volume of the vacuum vessel, in litres [l];
min
t is the flushing time, in seconds [s];
fl
Q is the flow of the flushed wastewater, in litres per second [l/s];
WW,fl
N is the number of forwarding pumps; and
WW
Q is the capacity of the forwarding pump, in litres per second [l/s].
WW,p
In reality, the conditions during air flushing are somewhat more complex. The water plugs need to be
accelerated, which means that the flow into the vacuum vessel is somewhat delayed. Air overtakes
water in the downslope sections and flows faster than the wastewater. After the end of the flushing
cycle the flow into the vessel does not immediately stop, because the air in the vacuum sewer expands.
However, the calculation with Formulae (14) to 19 is well on the conservative side.
6.6 Power consumption
The power consumption in Watts [W] of the vacuum and forwarding pumps can be estimated with the
following general Formulae (20) and (21), assuming adiabatic air compression in the vacuum pumps:
κ −1 /κ
( )
( )
AA
P κκ/ − 1⋅ Q ⋅ 0,/5⋅+pp 1− 0,/5⋅+pp p /η (20)
( ( ) ) ( ) ( ( ) )
A A A A,P,s max min max min aa A
where
P is the power consumption of the vacuum pumps, in Watts [W];
A
κ is the adiabatic coefficient of air = 1,4, dimensionless [-];
A
p is the ambient air pressure, in kilopascals [kPa]; and
aa
η
is the efficiency of the vacuum pump units, dimensionless [-].
A
P Q ⋅ρη⋅⋅gH / / 1 000 (21)
( )
WW WW,p p WW
where
P is the power consumption of the forwarding pumps, in Watts [W];
WW
η is the efficiency of the wastewater forwarding pump units; and
WW
H
is the total head at the pump unit in metres [m].
p
=
=
The efficiency of liquid ring pumps and sliding vane pumps is in the range 0,3 < η < 0,6 (for
A
p ≥ 30 kPa) whereby sliding vane pumps generally have better efficiency than liquid ring pumps. The
min
efficiency of rotodynamic forwarding pump units is in the range 0,2 < η < 0,5.
ww
7 Collection chambers on vacuum sewer systems
7.1 General
One or more properties may be connected to a collection chamber. Separate chambers shall be provided
to serve properties at different elevations where there is a risk of wastewater from one property
flooding another property. Where more than 20 persons are connected or where the wastewater flow
exceeds 3 m /d, a second interface valve unit shall be provided for redundancy.
NOTE National or local regulations or the relevant authority can specify requirements concerning the
number of properties connected to a collection chamber.
Ingress of surface water shall be prevented. Chambers should not be located where surface water can
collect.
7.2 Collection chambers
Examples of collection chambers are shown in Figure 5 to Figure 7.
Collection tanks serving domestic properties shall provide capacity to store a min
...
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