Sizing Tank Overflow Line For Gravity Flow

Hi All,

We have Tank that is designed to overflow to a small tank that drains to a sewer. The smaller tank is vented to atmosphere.  The system sketch is attached with this post. The overflow line is 6" Sch 10. I want to verify if the line is sized correctly. I read through paper by PD Hills " Designing Piping Systems for Gravity Flow". In the flow rate of the overflow is same as inflow rate which is 35 gpm. I calculated the line size as 4" by maintaining J_L^* to be less than 0.3 for side outlet piping from vessels in PD Hills paper. Also we want to install a 4" ON/OFF valve on the over flow at the bottom end as the overflow line size is required is only 4". The in flow valve will be closed when the 4" ON/OFF valve is closed. I can install a 6" valve too but a 4" would be cheaper and less heavier for installation and maintenance. The intention of installing the ON/OFF valve is have a control the drainage of the waste water until its P^H is brought to spec.

1. I want inputs from you all if you the 4" line size for self venting flow is correct or not.

2. I also want to know if by installing the 4" ON/OFF valve am I changing anything. I understand that when the valve opens after a while initially there will be full pipe flow followed by half-pipe flow.

Thanks and Regards,

Pavan Kumar

Edited by pxyarala, 05 November 2020 - 11:39 AM.

Hi,

Comments :  weird design . Remember KIS  (keep it simple) 

                     Why no vent on the storage tank ? 

                     Why not going directly to the sewer  /what the benefit of this degazer ?

                      what will happen if the on/off valve is kept close ( i.e air supply or actuator not operating )?

                      How will you keep the level stable and high ? a weir needs to be installed inside the tank ?

                      Do you have any issue with water contamination ? How do you manage he good mixing of the water ,                          how big is the tank ?

        Note : For sure your small pot is going to impact the "gravity "flow 

My view 

Breizh 

Edited by breizh, 06 November 2020 - 02:07 AM.

Hi breizh,

Please see my replies to your comments below.

Comments :  weird design . Remember KIS  (keep it simple) : This is how we have currently. I did not design this system.

                     Why no vent on the storage tank ? There is a vent on the tank which I have not shown. 

                     Why not going directly to the sewer  /what the benefit of this degazer ? The sewer line is beneath the small pot so can't drain                         directly to sewer.

                      what will happen if the on/off valve is kept close ( i.e air supply or actuator not operating )?

                      We will not be able to drain the Waste water through the over flow line.

                      How will you keep the level stable and high ? a weir needs to be installed inside the tank ? The water level is maintained at

                      the overflow line.

                      Do you have any issue with water contamination ? How do you manage he good mixing of the water ,                          how big is the tank ? The tank is part of the Neutralization system where we mix and get the PH of our Waste water to our specification before we drain to sewer.

        Note : For sure your small pot is going to impact the "gravity "flow . The level in the small pot is always below the inlet nozzle from the overflow line. In this case how will it impact?.

I need suggestions on sizing( verify the size of the existing line) the overflow line for gravity flow.

Thanks and Regards,

Pavan Kumar

Hi ,

a) you need to think big and provide the equipment needed for the operation ,  you said there is a vent on the tank .It should be indicated on your sketch  from the beginning.

On overflow must be free  to protect the tank . You did not reply to my question , what will happen if the ON/OFF valve is still close and you keep feeding the tank .

c) Instead of proposing modification , you should tell us what are the problems on the current set up and why ?

d) why the drain is not positioned at the bottom of the tank and why there is no separate overflow ?

e)  waste water is never clean water , you may accumulate solid , enough to create the blockage of the lines and other valve or pot . In other words you create additional resistances which are going to reduce your flow .

Only my views.

Breizh

Hi,

To support your work , a document about gravity drain  issued by Art , our mentor with comments about Hills's paper .

Good luck

Breizh 

Edited by breizh, 10 November 2020 - 12:54 AM.

Is anyone else getting an alarm from Kaspersky on Art's Gravity Flow.xls?

Hi Latexman,

Sorry about that , I've an antivirus on my PC ,no warnings .

Breizh 

Hi latexman,

After scanning my entire PC  I got one threat blocked and removed ! 

May be it was the one you mentioned .

have a good day

Breizh