A 50 ft diameter tank is located in a city to supply drinking water for a small community. The tank is 20 ft. high and is located 400 ft above the city. The tank supplies water with a constant flow of 4 cfs during the day. All the nodes in the network are located at 0 ft elevation. All the pipes have a roughness coefficient C = 100. Use Hazen-Williams formula during your calculations. Minor losses are neglected.
We assumed at the beginning that there was a constant demand in the city, but that is not accurate. It is possible to create a scenario where each hour is a multiplier from the minimum demand. The demands shown earlier in Figure 2 corresponded to the minimum demands in the city that occurred between midnight and 1 a.m. For the rest of the day, the demand is higher. Typical multiplying factors during each hour are shown in Table 2.
Below is the EPANET version of the above network.
To come to this point, following are the key steps:
Base demand at Junction 1 is negative due to the inflow of 4 cfs water from tank to the J1. J1 has water demand of 0.15 cfs, thus the total demand at this junction is 0.15-4 = 3.85 cfs
After setting up analysis, below are the results of nodes and links.
Pressure velocity simulation for given network
Pump Introduction in the System
Assume now that the maximum elevation of the tank is reduced to 340 ft. To change the elevation generates negative pressures in the node 17 at 8 a.m. It is desired to add a pump in pipe 21 to increase the head pressure.
Delete the pump and tank. Assume now that there is no tank. Replace the tank with a reservoir at the same elevation than the city. Because the city and the reservoir are at the same elevation, you will need a Pump to supply the water.