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?
You can model two tanks with one pump, in your case unless tank T6 is filling water will not go to tank T5.
So please put on-off controls on pump based on hydraulic grade levels of both the tanks.
Or you could put controls on adjacent pipes of tanks based on tank levels and when pipes adjacent to tanks are closed, pump should be off.
I will update you further once I put these controls in your model.
Bentley Technical Suppport
I have input controls into the model as you said but still, the model cant run successfully.Any other option?The problem is when I start running the model, tank 5 is empty and it is empty thought the period.How can I ensure flow is supplied to both tanks at the same time?2654.WATERCAD.zip
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).
Jesse DringoliTechnical Support Manager, OpenFlows ProductsBentley Communities Site AdministratorBentley Systems, Inc.
Answer Verified By: ALLAN MULONGO WAFULA
Thank you for the reply above.I was able to apply that concept to introducing a PSV at pipe-131.I also introduced a check valve immediately before the Tank T-5 to prevent backflow.When I ran the hydraulic analysis, it is so unfortunate that I still get errors from the engine.The main problem is that when T-6 is full, T-5 gets empty at certain step times.When T-6 gets full T-5 is empty yet I have input controls at the pump based on both tanks to prevent the pump present from going OFF when the 2-tanks are near to empty.
I think the problem arises from the controls.I lack proper controls in the model.Is there a way that I can allow the pump to pump water to both tanks-5 & T-6 (of different sizes, the 1st tank been in a lower elevation level than the 2nd one and both are about 3km apart) and at the same time be able to prevent one from getting empty as the other one will be getting filled?That is; a logical or compound control that will prevent T-5 from getting filled or completely empty as T-6 is filling and preventing T-6 from running empty or completely filled as T-5 is emptying or filling and while at the same time preventing the pump from going off??
Or, what do you think is wrong with this model here2022.WATERCAD.zip?
Just another question?Is it possible for me to set controls so that the pump can supply water to the two tanks at the same time and make them get filled 1st! then later on in a diffrent time step just to allow them to supply and meet the demands assigned to them with the pump staying off all throught this time(water only flowing/emptying from the tanks)?ANY IDEAS?
As mentioned by Jesse in his reply, you need to apply PSV on pipe – 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
I managed to solve the problem thanks to you and Jesse! The main challenge I was facing was with the introduction of the PSV in the model.I also adjusted your control set to read ">=99% " instead of the previous 20% in order to fully utilize Tank T6.The hydraulic engine ran successfully because of your suggestions and a few adjustments that I made on the junction demands in order to maintain them within the required range of the yield from the source.After all the above adjustments, parts of the network are no longer disconnected or face outages.Water is also flowing throughout the period.
This is the final designWatercad final.zip