Pump is used when one needs to transport the water from lower ground level to higher ground level. It can also be used when the level of the OSD is lower than the drain/river level that it has to discharge into.
The design of the pump is according to chapter 19 of MSMA 2nd edition. It essentially consists of a few parts: inflow hydrograph, storage estimation, pumping rate estimation and level pool routing.
For OSD with pump, the above pump design still applies, and in addition to that, the PSD and SSR is also checked in accordance with MSMA 2.
- Develop an inflow hydrograph
The inflow hydrograph is developed based on the rainfall data, which users can plug in all of the information in MITS. The inflow hydrograph is then developed based on the data and also is benchmarked as in Table 19.B1. The development of hydrograph also can be referred to as per Chapter 2.
2. Estimate Storage Volume and Stage-Storage Relationship
Trial and error is necessary for the storage volume estimation and stage-storage relationship can be developed which can be referred to in Table 19.B2.
Stage-Storage relations is plotted:
3. Estimate Pumping Rate and Number of Pumps
Given the storage volume, the estimated pumping rate and the number of pumps can be determined.
4. Estimate the Total Dynamic Head
Total Dynamic Head is the total equivalent height of fluid to be pumped. The calculation is the sum of the static head, velocity head and head losses in the pump discharge system due to friction. The equation can be referred to in MSMA 2nd Edition, Equation 19.1.
TDH = Hs + hf + hv + hl
Hs = Static head (m)
hf = Friction head (m)
hv = Velocity head (m)
hl = Losses through fittings, Valves, etc. (m)
Users can insert the value of the lowest level of storage, highest level of storage and the higher level that need to be pumped.
Based on the above elevation values, the TDH is calculated in accordance with the Equation 19.1. The calculation of the TDH and head losses are provided as reference.
5. Selection of Pump Performance Curve
Each pump has their own performance curve which has been developed by the manufacturer and to establish a reasonable balance between total dynamic head, discharge, efficiency, and energy requirements. Examples of curve sheet provided by manufacturer can be referred in MSMA 2nd Edition Figure 19.B5.
6. Pump Cycling
With the number of pumps set, the start and stop elevation are assigned as in Table 19.B3. Start level is the when the tank level reaches this value, the pump will start and stop level is when the tank level reaches this value, the pump will be stopped.
Stage-Discharge of rising and dropping water level is calculated based on the Pump Performance Curve given elevation and TDH, which is provided by the manufacturer. The relationship can be referred to Table 19.B4 (rising water level) and Table 19.B5 (dropping water level). Figure 19.B6 is the relationship shown in graph.
Stage – Pump Discharge relationship is plotted.
7. Storage Routing
Maximum water level can be estimated by routing the design, which is based on the Stage-storage and Stage-pump discharge relationship. Therefore, the sufficiency of the pump design can be estimated to meet the ARI flood protection criterion and thus the capital cost also can be optimised. The routing can be referred to Table 19.B6.
**The slight discrepancy is due to mismatching of the geometry, especially in the sizing of storage, where the manual calculation is considering the pump storage. However, the discrepancy is expected to be less than 5%