Backwash discharge pressure

[aghazawy]

Good Morning All,

i have a concern regarding the backwash discharge from water filters, will it be under pressure or not ?

i.e. when i am going to design the drain system, shall i consider the backwash as a forced main drain or to be discharged by gravity ?

 

[berkshire]

I do not know what type of filter you are dealing with, but in the ones that I have experienced, backwashing merely diverts the flow from one face of the filter to another. This flushes off the accumulated contaminants. The concern would be the outlet size on the drain, if it is smaller than the pump discharge then you could get unwanted pressure buildup in the filter casing.
B.E.

You are judged not by what you know, but by what you can do.

 

[aghazawy]

the issue is for a sand filter for swimming pool, while the main problem is the pump room at basement level and i have a confusion regarding the drain of the filters, shall i discharge to the existing sump pit or to consider the backwash as a forced main and to be elevated to the sewer manhole.

 

[Compositepro]

What is confusing you? You can discharge to where ever you wish and the pressure at any point will depend on your design, due to elevation changes and resistance of pipes to flow. The most important factor for the filter is that the flow rate is within the limits needed to fluidize the sand but not blow it down the drain. There probably should be an air gap somewhere in the drain piping so you know that the pressure is at ambient and you do not create a siphon.

 

[aghazawy]

Dear Compositerpro,
i am not sure from water pressure after the backwash, i think there should be a pressure drop through the filter and then the discharge pressure is minimized.

 

[IRstuff]

Seems to me that the pressure is irrelevant, since you will not be backwashing against a pressure, since the inlet water must be disconnected from the filter during backwashing so that the effluent is appropriately disposed of.

TTFN
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