SIST EN 16932-2:2018

SLOVENSKI STANDARD
01-junij-2018
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SIST EN 1091:2000
SIST EN 1671:1998
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Drain and sewer systems outside buildings - Pumping systems - Part 2: Positive
pressure systems
Entwässerungssysteme außerhalb von Gebäuden - Pumpsysteme - Teil 2:
Druckentwässerungssysteme
Réseaux d'évacuation et d'assainissement à l'extérieur des bâtiments - Systèmes de
pompage - Partie 2 : Systèmes sous pression
Ta slovenski standard je istoveten z: EN 16932-2:2018
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 16932-2
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 2: Positive pressure systems
Réseaux d'évacuation et d'assainissement à l'extérieur Entwässerungssysteme außerhalb von Gebäuden -
des bâtiments - Systèmes de pompage - Partie 2: Pumpsysteme - Teil 2: Druckentwässerungssysteme
Systèmes sous pression
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 16932-2:2018 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 of positive pressure systems . 8
6.1 Type of pumping station . 8
6.1.1 Introduction . 8
6.1.2 Pumping stations with submersible pumps . 9
6.1.3 Pumping stations with dry installed pumps . 11
6.1.4 Other types of pumping stations . 11
6.2 Selection of type of pumping station . 12
6.3 Route and profile of rising mains . 12
7 Hydraulic design of pumping systems . 13
7.1 Introduction . 13
7.2 Establish inflow rates . 15
7.2.1 Foul wastewater pumping stations . 15
7.2.2 Surface water pumping installations . 15
7.2.3 Combined sewer pumping stations . 15
7.3 Select desired pump flow rates . 15
7.4 Dimensioning collection tank . 15
7.5 Select rising main diameter. 16
7.5.1 Pumping stations . 16
7.5.2 Pressure sewer systems . 17
7.6 Retention period . 17
7.7 Calculation of system characteristics . 18
7.7.1 System head calculation . 18
7.7.2 Pressure sewer systems . 20
7.8 Selection of pump units and duty points . 20
7.9 Check pressure transients (waterhammer) . 22
8 Detailed design of pumping stations . 23
8.1 General . 23
8.2 Layout . 23
8.3 Collection tank . 24
8.4 Pump units . 25
8.4.1 Pumps . 25
8.4.2 Air compressor units . 25
8.5 Controls and electrical equipment and instrumentation . 25
9 Septicity . 26
9.1 General . 26
9.2 Control of septicity. 27
9.2.1 General . 27
9.2.2 Limiting retention period . 27
9.2.3 Air flushing . 27
9.2.4 Chemical treatment . 28
9.2.5 Hydrogen sulphide stripping . 28
9.2.6 Dilution of the septic wastewater in fresh wastewater . 28
10 Testing and verification . 28
10.1 Pumping stations . 28
10.2 Rising mains . 28
10.3 Commissioning . 28
11 Operation and maintenance manual . 29
Bibliography . 30

European foreword
This document (EN 16932-2:2018) 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 16932-3:2018, this document supersedes EN 1091:1996 and
EN 1671:1997.
EN 16932, 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 positive pressure 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 1610:2015, Construction and testing of drains and sewers
EN 12050-1:2015, Wastewater lifting plants for buildings and sites — Part 1: Lifting plants for
wastewater containing faecal matter
EN 12050-2, Wastewater lifting plants for buildings and sites — Part 2: Lifting plants for faecal-free
wastewater
EN 12050-3, Wastewater lifting plants for buildings and sites — Part 3: Lifting plants for limited
applications
EN 12050-4, Wastewater lifting plants for buildings and sites — Part 4: Non-return valves for faecal-free
wastewater and wastewater containing faecal matter
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 16933-2:2017, Drain and sewer systems outside buildings — Design — Part 2: Hydraulic design
EN ISO 9906:2012, Rotodynamic pumps — Hydraulic performance acceptance tests — Grades 1, 2 and 3
(ISO 9906:2012)
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:
aerobic; maintenance;
anaerobic; pumping station;
collection tank; relevant authority;
combined system; retention period;
confined space; rising main;
drain; septic wastewater;
dry weather flow; sewer;
extraneous flow; sewer system;
gradient; wastewater treatment plant.
infiltration;
Note 2 to entry: The following terms used in this part of this standard are defined in EN 16932-1:2018:
collection chamber; pump;
duty point; pump unit
forwarding pump; pumping system;
level sensor; vacuum station.
lift station;
profile;
3.1
ball passage
passage where a ball with a defined diameter can pass through without deformation
[SOURCE: EN 12050-1:2015, 3.1.9]
3.2
foul wastewater
wastewater comprising domestic wastewater and/or industrial wastewater
[SOURCE: EN 16323:2014, 2.1.2.6]
3.3
net positive suction head
NPSH
amount of the absolute value of the total head above the head equivalent to the vapour pressure of the
liquid at the particular temperature, with reference to the NPSH-datum plane
[SOURCE: EN ISO 17769-1:2012, 2.2.2.1]
3.4
NPSH datum plane
horizontal plane through the centre of the circle described by the external points of the entrance edges
of the impeller blades, in the first stage in the case of multi-stage pumps
[SOURCE: EN ISO 17769-1:2012, 2.2.2.1]
3.5
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]
3.6
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
a wave speed of pressure transients, in metres per second [m/s]
D internal diameter of the pipe (bore), in metres [m]
D internal diameter of the pipe (bore) in section i, in metres [m]
i
E 2
P elastic modulus of the pipe material, in Newtons per square metre [N/m ]
E 2
W elastic modulus of wastewater, in Newtons per square metre [N/m ]
f maximum permitted frequency of pump starts per hour [1/h]
g 2
acceleration due to gravity, in metres per second squared [m/s ]
H total head of the system, in metres [m]
s
H total head at the pump unit, in metres [m]
p
H required pump head in an air flushed rising main, or a rising main where air or gas
A
accumulation can occur, in metres [m]
h local head loss in the bends, valves and other fittings, in metres [m]
f
h head loss, in metres [m]
l
h head loss due to friction in the pipe, in metres [m]
p
h level difference between the end of the rising main and pump unit(s), in metres [m]
z,rm
Σh sum of the level differences of all downsloping sections in the rising main which can be
A,i
filled with air or gas, (i.e. the level differences between all their high and subsequent low
points), in metres [m]
h hydrostatic head, in metres [m]
z
Σk sum of the local head loss coefficients in bends, valves and other fittings in the pipeline
p
(dimensionless) [-]
Σk sum of the local head loss coefficients in bends, valves and other fittings in section i,
p,i
dimensionless [-]
L length of the pipeline, in metres [m]
L length of section i of the rising main, in metres [m]
i
L length of the pipeline before or after a closing device, in metres [m]
t
ΣL sum of the lengths of the downsloping sections in section i, which can be filled with air, in
A,i
metres [m]
P power consumption of the pump unit, in Watts [W]
P
Δp Joukowski surge pressure, in Pascals [Pa]
max
Q 3
p pump flow rate, in cubic metres per second [m /s]
Q mean capacity of the active pump between switch on and switch off levels for the pump, in
pm
cubic metres per hour [m /h]
s wall thickness of the pipe, in metres [m]
t reflection period of the pressure wave, in seconds [s]
R
V working volume of the collection tank, which is the volume between the lowest pump
c
switch on level and the lowest switch off level, in cubic metres [m ]
v velocity in the direction of flow averaged across the flow cross-section, in metres per
second [m/s]
v velocity needed for air removal, in metres per second [m/s]
AR
v velocity of the design wastewater flow in section i, in metres per second [m/s]
i
Δv change in flow velocity, in metres per second [m/s]
α angle of the downsloping section downstream of a high point, in degrees
η efficiency of the pump unit, dimensionless [-]
P
λ friction coefficient, which is the pipeline headloss per unit length, dimensionless [-]
λ friction coefficient in section i, dimensionless [-]
i
μ lateral contraction coefficient of the pipe material, dimensionless [-]
ρ 3
density of wastewater, in kilogrammes per cubic metre [kg/m ]
5 General
This European Standard shall be read in conjunction with EN 16932-1. Positive pressure systems shall
comply with the requirements of EN 16932-1 as well as the requirements of this European Standard.
6 Planning of positive pressure systems
6.1 Type of pumping station
6.1.1 Introduction
Typical pumping station types include the following:
— pumping stations with submersible pumps;
— pumping stations with dry installed pumps;
— pumping stations with screw pumps;
— pumping assemblies;
— ejector tank stations.
6.1.2 Pumping stations with submersible pumps
Pumping stations with submersible pumps are the most common type of pumping stations in drain and
sewer systems. They comprise one or more submersible rotodynamic pump units in a collection tank.
The pump units are connected to the rising main using fittings that allow the pump units to be removed
from, and replaced in the collection tank from the surface without the need for personnel to enter the
collection tank.
Key
1 collection tank 4 non-return valve
2 pump unit 5 isolating valve (alternative positions shown)
3 level sensor (pressure sensor shown, other 6 controls and electrical equipment and
methods are possible) instrumentation cabinet
Figure 1 — Example of pumping station with submersible pumps and no external valve chamber
The non-return valves can be installed either in the collection tank (see Figure 1) or in an adjacent valve
chamber (see Figure 2), allowing easier access for maintenance. Isolating valves can be buried directly
in the ground or installed in the collection tank (see Figure 1), or installed in a separate valve chamber
(see Figure 2). The choice depends on the anticipated frequency of maintenance and the availability of
access. The position of non-return valves should be sufficiently low to ensure tight closure.
An isolating valve can also be fitted on the incoming gravity drain or sewer.
Such pumping stations are suitable for a wide range of applications within the sewer network.
Key
1 collection tank 5 isolating valve
2 pump unit 6 controls and electrical equipment and
instrumentation cabinet
3 level sensor (float switch shown, other methods 7 valve chamber
are possible)
4 non-return valve
Figure 2 — Example of pumping station with submersible pumps and external valve chamber

Key
1 collection tank 4 non-return valve
2 pump unit 5 isolating valve
3 level sensor (float switch shown, other methods
are possible)
Figure 3 — Example of a pumping station for use in pressure sewer systems
Figure 3 shows an example of a pumping station with submersible pumps for use in pressure sewer
systems.
6.1.3 Pumping stations with dry installed pumps
Pumping stations with dry installed pumps (see Figure 4) comprise a collection tank and one or more
rotodynamic pump units installed in an adjacent dry well. The pumping station valves are also installed
in the dry well. The advantage of this type of pumping station is that the pump units and associated
equipment can be installed in a cleaner and less hazardous environment.

Key
1 collection tank 5 isolating valve
2 pump unit 6 controls and electrical equipment and
instrumentation cabinet
3 level sensor (ultrasonic sensor shown other 7 dry well
methods are possible)
4 non-return valve
Figure 4 — Example of a pumping station with dry well installed pumps
6.1.4 Other types of pumping stations
Other types of pumping stations for special applications are available. These include:
a) In an ejector tank station wastewater flows by gravity into one or more sealed tanks. Each tank is
periodically emptied by closing its inlet and ventilation pipe, and admitting compressed air into the
top of the tank. This forces the wastewater from the bottom of the tank into the rising main.
National or local regulations or the relevant authority can require the periodic inspection of
pressure vessels. Ejector tank stations are suitable for high head and low flow applications. Ejector
tanks can also be used in vacuum stations instead of forwarding pumps, but are not usually used on
pressure sewer systems. Ejector tank stations have the additional advantage that they can also be
used for air flushing of the rising main by admitting more compressed air than is necessary to
empty the ejector tanks.
b) Pumping assemblies comprise a collection tank, pump units and valves in a single assembly. They
can be used for small applications (e.g. serving a single building). They can be installed in a dry
chamber on the drain from a building or site. Pumping assemblies shall be manufactured in
accordance with EN 12050 (all parts).
c) Progressive cavity pumping stations comprise a collection tank with a progressive cavity pump unit
with grinder at the pump inlet. The pump is typically powered by an electric motor. The rising main
is equipped with an isolation valve. They can be used for small applications (e.g. serving a single
building and in pressure sewer systems). Since they can develop very high pressures an automatic
over-pressure cut-out is required to avoid damage to the rising main. Progressive cavity pumps
have some suction lift capability. They can therefore be installed above ground.
6.2 Selection of type of pumping station
The type of pumping station should be selected taking account of the performance requirements, any
external constraints and the following criteria:
a) space available;
b) location in relation to the main traffic flow (e.g. pumping station not in the middle of the road, but
on the side)
c) geotechnical conditions on the site (e.g. groundwater level, load bearing capacity);
d) integration of pumping stations into other infrastructure (e.g. integration in a road underpass)
e) hydraulic performance requirements (i.e. the required head and flow rate);
f) whether it is necessary to create pressure or just lift the wastewater;
g) solids handling requirements;
h) access required for maintenance;
i) whole life costs (including initial costs,, operation and maintenance costs);
j) power consumption;
k) health and safety;
l) environmental impact.
6.3 Route and profile of rising mains
The route and profile of rising mains shall consider the following.
a) The profile shall provide adequate depth of cover to the pipe to protect the pipe from imposed
loads, frost and to avoid interference with other utility services.
b) Air or gas accumulation in rising mains reduces their capacity and creates conditions for corrosion
of the main. The profile and flow conditions of the main should ensure that air or gas accumulation
does not affect the performance of the main. Air or gas accumulation should be managed by one or
more of the following approaches:
1) minimizing the entry of unwanted air into the system by careful hydraulic design of the
collecting tank to reduce splashing and air entrainment;
2) preventing generation of gas by control of the formation of septic wastewater;
3) avoiding prominent high points in the profile of the rising main;
4) design of the rising main with very little downslope and a flow velocity that is sufficient to
drive air or gas through the rising main, thus preventing air or gas accumulation behind high
points;
5) provision of air valves at unavoidable prominent high points to remove accumulated air or gas;
6) operation of pumps in a manner that avoids drawing in air.
c) Sediment deposits reduce the capacity of the rising mains. The profile and flow conditions in the
main should ensure that sediment build-up does not occur. If sediment build up cannot be
prevented, provision should be made for appropriate maintenance activities for its removal. If
cleaning is to be carried out by pigging then provision should be made for insertion and removal of
the pig.
d) Where air valves or washout valves are provided the route shall ensure that appropriate access can
be provided to the locations where valve chambers are required for operations and maintenance
purposes and at locations where pigs are to be inserted or removed (see EN 16932-1:2018, 9.5.2).
e) Where air valves, washout valves and discharge points are in proximity to occupied buildings or are
in another location that can cause nuisance, the provision of means for control of odour and noise
should be considered.
7 Hydraulic design of pumping systems
7.1 Introduction
The performance of a pump and its associated rising main are interrelated. The basic hydraulic design
of the pumping station and of the rising main shall therefore be considered together.
The hydraulic design process is illustrated in Figure 5.
Figure 5 — Process for hydraulic design of pumping stations
7.2 Establish inflow rates
7.2.1 Foul wastewater pumping stations
Foul wastewater flow rates into the pumping station shall be established in accordance with
EN 16933-2. The design peak, the minimum and the average foul wastewater flow rates shall be
established. Infiltration and other extraneous water flows shall also be taken into account. Where the
variation in the rate of flow is sufficiently large that more than one pump is to be used to pump the foul
wastewater flow, the diurnal variation in foul wastewater inflow shall be established.
National or local regulations or the relevant authority can specify requirements for design foul
wastewater flows in pumping stations.
7.2.2 Surface water pumping installations
Design surface water inflow rates shall be determined to ensure that the hydraulic design criteria for
the upstream system are achieved (see EN 16933-2).
7.2.3 Combined sewer pumping stations
The design wastewater inflow rate shall be the sum of the design foul wastewater inflow rate,
established in accordance with 7.2.1 and the design surface water inflow rate, established in accordance
with 7.2.2.
7.3 Select desired pump flow rates
A single pump or a group of pumps should be selected to provide the required flow capacity. The
capacity of the pumping station should be determined as part of the hydraulic design of the whole drain
and sewer system in order to meet the design criteria (see EN 16933-2).
The need for additional pump units to provide resilience shall be considered. Where there is a
significant variation in wastewater inflow rate, the option of operating more than one pump at times of
high wastewater inflow (duty assist operation) or the use of a variable speed pump should be
considered.
In pumping stations with low wastewater inflow rates, the minimum pump ball-passage to achieve the
required solids handling capacity (see 7.5.1 (a)) can determine the minimum pump rate, which depends
on the type of pump used. Grinder pumps have comparatively low minimum pump rates.
National or local regulations or the relevant authority can specify requirements for pump rates in
pumping stations.
7.4 Dimensioning collection tank
The maximum design water level for the pumping station should be established, taking into account its
effect on the performance of the upstream gravity system.
The volume of the collection tank (V ) between the lowest pump switch-off level and the highest pump
c
switch-on level shall be selected so that the number of starts per hour does not exceed a maximum
number set by the designer (f). The maximum number depends of the amount of heat generated in the
motors and starters and on the type of starter (soft starters and frequency converters generate less heat
than star-delta starters) and the power of the motor. A maximum value of 12 to 15 starts per hour is
commonly used in many countries though this should be reduced for larger pumps. The number should
be set taking into account:
a) the number specified by the operator of the system;
b) the number specified by the pump unit manufacturer;
c) any limitations imposed by the electricity distribution operator;
d) the energy used for repeated acceleration of the wastewater;
e) limiting the size of the collection tank to limit cleaning requirements and to limit the retention
period to avoid the formation of septic wastewater;
f) any limitations on the depth of the tank;
g) the space available.
The working volume can be calculated from Formula (1):
V 0,/25⋅ Qf
c pm
(1)
where
V is the working volume of the collection tank, which is the volume between the lowest pump
c
switch on level and the lowest switch off level, in cubic metres [m ];
Q is the mean capacity of the active pump between switch on and switch off levels for the
pm
pump in cubic metres per hour [m /h];
f is the maximum permitted frequency of pump starts per hour [1/h].
The working volume can be reduced by provision of multiple pumps operating in sequence (without
exceeding the maximum number of starts per hour on any one pump) or by provision of variable speed
pumps.
7.5 Select rising main diameter
7.5.1 Pumping stations
The internal diameter of the rising main shall be selected taking into account the following factors:
a) The internal diameter should be large enough to limit the occurrence of blockages taking into
account the following:
1) whether a grinder pump is used or not;
2) the diameter of the rising main which should not be smaller than the opening size through the
pump and which should be larger than the internal diameter of its suction pipe (where
applicable);
3) the nature of the wastewater (e.g. the presence of grease) and the nature and size of the solids
in the wastewater.
NOTE 1 National or local regulations or the relevant authority can specify requirements on the minimum
internal diameter.
b) The velocity in the rising main shall be sufficient to achieve self-cleansing conditions at least once
per day.
c) Self-cleansing conditions depend on the pipe gradient and diameter, the velocity and the nature of
the sediment in the wastewater, which can be highly variable.
=
From experience, this can usually be achieved in pipes with up-slopes up to 30° in intermittent flow
conditions if a velocity of between 0,6 m/s and 1,2 m/s is achieved at least once per day. In higher
pipe gradients, a higher velocity is required. The balance between lower cleaning and capital costs
and increased energy costs from higher velocities should be considered.
NOTE 2 National or local regulations or the relevant authority can specify further requirements on self-
cleansing conditions.
d) The velocity shall be limited to reduce unnecessary energy use.
e) The maximum retention period shall not be exceeded at low inflow (see 7.6). Where the maximum
retention period is exceeded, the rising main diameter should be reduced. If this is not feasible or
not economical (pump head rises), measures should be taken to control the formation of septic
wastewater (see 9.2).
f) Capital and operational costs.
For most pumping installations, only one rising main is provided. Where the range of flow variation is
so wide that it is not possible to achieve sufficient flow velocity in the rising main during low flow
without exceeding maximum velocity during peak flow, multiple rising mains should however be
considered. Where the second main is used infrequently, it should be drained down between uses to
avoid the formation of septic wastewater.
Pressure mains shall have an internal diameter equal to or exceeding the internal diameter of the outlet
of the pump.
7.5.2 Pressure sewer systems
Pressure sewer systems are dimensioned for the peak design flow expected from the connected
properties (see 7.2.1). Where the peak design flow is lower than the flow of the individual pump, the
pump flow shall be used to design the rising mains.
The rising mains should be sized so that the self-cleansing velocity is achieved in each section of the
rising main during peak flow. In systems that are designed for air flushing (see 9.2.3) the peak flow
occurs during air flushing.
NOTE National or local regulations or the local authority can limit the use of air flushing.
7.6 Retention period
Retention periods in collection tanks and rising mains shall be kept to a minimum in order to minimize
the formation of septic wastewater and gas (see Clause 9). Where the flow passes through more than
one pumping station in sequence the cumulative effect of the retention period shall be considered for all
flow paths.
In single pumping station systems if the maximum retention period is exceeded at minimum flow, a
reduction of the rising main diameters should be considered. In some cases, it is not possible to control
the formation of septic wastewater in this way as the total head or the power consumption would be
too high. In some cases, where extreme flow variation is experienced, e.g. at holiday sites, it is not
practicable to keep retention periods to an acceptable level during periods of low flow. For combined
systems a dual rising mains system can be used to limit retention periods in rising mains.
Where it is not practicable to limit the retention period other measures to control or manage the
formation of septic wastewater (see 9.2) should be considered.
7.7 Calculation of system characteristics
7.7.1 System head calculation
A system’s characteristic is a graphical representation of the system head (H ) expressed as a function
s
of the flow rate (Q) that is (H = f(Q)), which is commonly called the system’s H-Q-curve.
s
The pumps in a pumping station shall be capable of delivering the design flow rate at the system's total
head. The system’s total head (H ) is the sum of the static head (h ), the head loss (h ) and the head
s z l
required to accelerate the flow (v /2g) and is given by Formula (2):
v
H= hh+ + (2)
s zl
2⋅ g
where
H is the total head of the system, in metres [m];
s
h is the hydrostatic head, in metres [m];
z
h is the head loss, in metres [m];
l
v is the velocity in the direction of flow averaged across the flow cross-section, in metres per
second (m/s);
g 2
is the acceleration due to gravity, in metres per second squared [m/s ].
During pumping station operation, the static head (h ) varies with the wastewater level in the collection
z
tank. The system curve therefore moves within a zone bounded by upper and lower limiting system
curves, corresponding to the minimum and maximum wastewater levels in the collection tank.
The head loss (h ) comprises two parts, the pipeline head loss due to friction loss in the pipe (h ) and
l f
the local head loss due to bends, valves and other fittings (h ) (see EN 16933-2:2017, Clause 7). The
p
head loss shall include the loss in the pump suction and delivery pipes within the pumping station, see
Formula (3) or (4).
hh+ h
l pf
(3)
where
h is the head loss, in metres [m];
l
h is the head loss due to friction in the pipe, in metres [m];
p
h is the local head loss in the bends, valves and other fittings in metres [m];
f
or

λ⋅ Lv
hk+∑ (4)

l p
D 2⋅ g

where
=
=
λ is the friction coefficient, which is the pipeline headloss per unit length. This can be
1)
calculated with the Colebrook-White formula (see EN 16933-2:2017, 7.2.5);
NOTE 1 This is dependent upon the Reynolds number and the operational hydraulic pipeline roughness of
the interior pipe surface.
D is the internal diameter of the pipe (bore), in metres [m];
L is the length of the pipeline, in metres [m];
Σk is the sum of the local head loss coefficients in bends, valves and other fittings in the pipeline,
p
dimensionless [-].
The hydraulic pipeline roughness in the pipe is specified by the manufacturer for new pipes. The
roughness can change over time and after some years of usage it can be between 0,1 mm and 1,5 mm.
The head loss can be influenced by factors, such as the quality of installation and operational conditions.
Head losses can increase significantly due to unplanned low and high points, particularly when
trenchless installation is used; and due to sedimentation, caused by insufficient velocity.
Air or gas pockets can develop downstream of high points in the pipeline. This increases the system's
total head. The additional head is the sum of the heights of all the downsloping sections that can be
filled with air.
NOTE 2 National or local regulations or the relevant authority can specify methods for head calculations taking
account of gas/air pockets.
At high flow, air can be driven out through downsloping sections. Whether and how fast this happens,
depends mainly on pipe diameter, downslope and flow rate. Various empirical formulae have been
developed to determine the minimum velocity (v ) for transport of gas pockets in rising mains.
AR
For an example (see Pothof 2011) which may be used in rising mains up to DN 250. For rising mains
with a slope between 5° and 25° see Formula (5):
v = 09,⋅⋅gD
AR
(5)
where
v is the velocity needed for air removal, in metres per second [m/s];
AR
Where the slope is less than 5° the minimum velocity is, see Formula (6):
v = 06,⋅⋅gD (6)
AR
Alternatively the formula produced by Aigner and Thumernicht (2002) may be used, see Formula (7):
D⋅ sinα
vg1,5⋅⋅ (7)
AR
1,64⋅+sin α 0,06
( )
where
α is the angle of the downsloping section downstream of a high point, in degrees;
If a system is designed for air flushing, or if air or gas can accumulate at high points or slope sections of
the rising main, the wastewater pumps shall be selected such that they can overcome the head loss
calculated with Formula (8):
1) This formula is named Colebrook in the French version and Prandtl-Colebrook in the German version.
=
 

λ ⋅ LL−∑
( )
v
i i A,i
 
i 
H =∑ ⋅ +∑ k +∑ hh+ (8)
 
A p,i A,,i z rm
2⋅ gD

 i 

 
where
H is the required pump head in an air flushed rising main, or a rising main where air or gas
A
accumulation can occur, in metres [m];
v is the velocity of the design wastewater flow in section i, in metres per second [m/s];
i
λ is the friction coefficient in section I, dimensionless [-];
i
L is the length of section i of the rising main in metres [m];
i
D is the internal diameter of the pipe (bore) in section i, in metres [m];
i
Σk is the sum of the local head loss coefficients in bends, valves and other fittings in section i
p,i
(dimensionless);
ΣL is the sum of the lengths of the downsloping sections in section i, which can be filled with
A,i
air, in metres [m];
Σh is the sum of the level differences of all downsloping sections in the rising main which can
A,i
be filled with air or gas, (i.e. the level differences between all their high and subsequent low
points), in metres [m];
h is the level difference between the end of the rising main and pump unit(s), in metres [m].
z,rm
The velocity during air flushing shall be sufficient to remove any sediments that have accumulated in
the rising main.
7.7.2 Pressure sewer systems
The head loss in pressure sewer systems should be calc
...