Regeneration Flow Rate

[Shopco]

What is the proper backwashing flow rate for a GAC filter? The filter is a 3cf, 14â€x65†tank and I am using 20x50 mesh GAC. Should I use the distributor from Ohio Pure Water (1½ Inch Commercial Hub and Lateral Distributors (D717807)

http://www.ohiopurewater.com/shop/customer/search.php?substring=D717807

 

[Reach4]

See figure 4 in http://www.wcponline.com/pdf/0607Michaud.pdf

Your 14 inch OD tank will have a cross section of about 1 square foot. (1 square ft would correspond to 13.54 inches ID) So for 50% expansion, you would want 6 GPM. I am not a pro, and I could be mis-thinking this.

 

[Sponsor]

 

[Shopco]

Great Link Reach4! I have spent some time looking for this info. It’s funny; I was thinking that the finer mesh would require a greater backflow. The Fleck 2510 I was planning on ordering comes with a backflow rate of 10gpm and I was concerned that this might be inadequate. Now I am thinking it might be too much! Do you (or anyone) know how to control the backwash flow rate? Is it pre-set?

 

[Mialynette2003]

My book says 10 GPM for a 14x65 with carbon.

 

[Shopco]

How is the flow rate set? Does the Fleck 2510 backwash at 10gpm, as the dealer says or can it be adjusted?

 

[Mialynette2003]

The max backwash flow on a 2510 valve is 17 GPM. To reduce the flow to 10 GPM, a backwash flow control is installed.
http://www.pentairwatertreatment.co...reatment/Literature/2510 Spec Sheet 40729.pdf

 

[Shopco]

See figure 4 in http://www.wcponline.com/pdf/0607Michaud.pdf

According to this chart the differences in proper flow rate vs mesh size is significant. The generic setting for a GAC filter seems to be 10gpm but that is for 12x40 mesh which (if I am reading the chart correctly) yields a bed expansion of 40% . Using 10gpm flow rate for 20x50 mesh yields a bed expansion of over 100%. Wouldn’t a 100% bed expansion result in carbon being forced into the drain unless there was a screen to prevent it?

 

[ditttohead]

14" tank has a sq. ft. area of 1.068, at 10 GPM per Sq. ft. a 10 GPM Backwash rate is correct, assuming water temperature is 60-ish. which is a 40% expansion.

 

[Shopco]

The Fleck 2510 uses “buttons” to set the backwashing flow rate up to a maximum of 17gpm. They are washer-like pieces, come in a wide selection of flow rates, and are inexpensive ($2.50). Ohio Pure Water, from whom I am buying my GAC filter, made a brilliant suggestion. Leave the valve wide-open and install a ball valve in the drain line. While in full backwashing mode, open the valve until carbon just starts to come out, then close it a bit. So kudos to Chuck at www.ohiopurewater.com for solving that problem.

My plan is to take the ball valve suggestion and when it is properly set, measure the (backwash) flow rate. I will then install enough 4½” x 20” BB (Big Blue) 5µ sediment filters, in parallel, to supply either that flow rate or my household’s maximum SFR, whichever is greater (I suspect it will only take one BB but it might take two).

As an aside, I have some difficulty determining the flow rates of various filters. I know from experience that given enough pressure I can draw >10gpm through a 2”x10” 1 micron sediment filter but at that rate I doubt that it is filtering out very many 1µ particles. Axeon has some useful data.

 

[Reach4]

14" tank has a sq. ft. area of 1.068, at 10 GPM per Sq. ft. a 10 GPM Backwash rate is correct, assuming water temperature is 60-ish. which is a 40% expansion.

So we can infer that a 14 inch tank is 14 inches ID. I was not sure which way it was, though at larger diameters the difference is less significant.

You disagree with figure 4 in http://www.wcponline.com/pdf/0607Michaud.pdf on 20x50 mesh GAC, and I expect your number is based on manufacturer's data. Glad to see better info.

Would it be good for shopco to use a fine top basket in case? What basket would be good?

 

[Shopco]

Unless the bed expansion is greater than the available freeboard a top basket would serve no purpose. Using 3 cf. of media in a 14"x 65" tank will yield >50% available expansion. By employing the method stated in post #9 the backflow rate will be maximized by using all of the available freeboard without exceeding it.

 

[ditttohead]

So we can infer that a 14 inch tank is 14 inches ID. I was not sure which way it was, though at larger diameters the difference is less significant.

You disagree with figure 4 in http://www.wcponline.com/pdf/0607Michaud.pdf on 20x50 mesh GAC, and I expect your number is based on manufacturer's data. Glad to see better info.

Would it be good for shopco to use a fine top basket in case? What basket would be good?

Whoops, my mistake, My mind kept saying 12x40. 20x50 mesh is not commonly used in residential applications due to the high pressure drop potential across the bed. As the article states, a 10" tank should be limited to 5 GPM flow, a 12x40 mesh will flow much more without the pressure drop.

Do not use a ball valve to limit flow rates. A flow control button regulates flow regardless of pressure. A fixed orifice will vary greatly depending on pressure.