Can a pump serve more than two tanks on the downstream side served by a single rising main pipe

Question

Hello Bentley family, 
 Can a single pump be able to pump water to two or more tanks placed further downstream from the first tank all located along the same rising main line but the tanks having higher physical elevation than the 1st tank? 
 Please have a look at the attached file in order to have a better understanding of my question Khasoko Buyofu.zip 
 My question is, After choosing the right pump that is enough to pump water up to the furthest and highest point in the model with the inclusion of all loses; why is watercad unable to allow water to flow to the 2nd tank?Is it because pressure gets back to zero when the surface of water comes in contact with the atmosphere at the tank?What measures should I use then or controls?Should I introduce a gate valve?

Jesse Dringoli · Accepted Answer

Hello Allan, 
 The problem is that the first tank is at a much lower elevation than the second tank, and you are using the top-fill option on the second tank. The pump is adding enough head to fill tank T-6, which is at an elevation of 1259 m. Tank T-5 further downstream can only fill if the HGL is above the base elevation plus the inlet invert level = 1289 m (see details on top-fill tanks here ). So, since the HGL is 1259, flow is not able to pass into the other tank and hence you see zero flow in the piping between T-6 and T-5 (and thus T-5 drains to empty). 
 In order to balance energy across this system, the above must be true. 
 If for example you place a PSV on pipe P-131 (leading to T-6) with an HGL setting of 1295 m, then the pump will be able to add more head to "lift" the water to the downstream tank T-5. However, it won't be able to add enough to prevent that tank from becoming empty. If you increase the PSV elevation setting, it will get to the point where the PSV closes though and flow only goes to T-5 (and still is not enough to prevent the tank from becoming empty given the demands placed on the tank itself and the downstream network).

Sushma Choure · Answer

Hello Mulongo, 
 As mentioned by Jesse in his reply, you need to apply PSV on pipe &ndash; 131 it will increase the HGL to 195 m, basically pump will add head required for the water to reach at T5. 
 Here is the copy of the updated model, In which I placed PSV at P-131 and a control saying if tank T6 Percent full >= say 20 %, close pipe -131 and pipe P-57 open (adjacent to tank T5). 
 In this case since pump needs to add around 62 m of head due to PSV setting, you should change the pump definition as well. I created a single point pump curve with required head 65 m to be on the safer side and considering headloss and flow of 4 m3/h. In this case also total demand throughout the time steps is not served, so you may tweak it further as required. 
 Hope this helps. 
 Khasoko Buyofu NO sump tank- revised.zip

Can a pump serve more than two tanks on the downstream side served by a single rising main pipe

Top Replies