BS/EN 16932-2-2018 pdf download.Drain and sewer systems outside buildings-Pumping systems Part 2 : Positive pressure systems.
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 Z.2J. and the design surface water inflow rates established in accordance with Z2.2.
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 Z5.J. (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 (Va) between the lowest pump switch-off level and the highest pump switch-on level shall he selected so that the number of starts per hour does not exceed a maximum number set by the designer (1).
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 7.21). 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 Clause9). 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 of the flow rate (Q) that is (H =1(Q)). which is commonly called the system’s H.Q-curve.BS/EN 16932-2-2018 pdf download.
BS/EN 16932-2-2018 pdf download
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