Pea Gravel in Sand Filter, etc.

[TomU]

Hi all!

I recently picked up a new 24" sand filter. I've noticed that filters 30" and larger tend to use a layer of pea gravel in the bottom of them before the sand is added to better distribute the hydraulic pressure on the sand when backwashing the filter. Does anyone know if this would be beneficial to do in a 24" filter, or if the filter is small enough that it won't really matter? If it is good to do, should the pea gravel come all the way up to the laterals, go over the laterals, etc.?

Also, I'm thinking of running a low speed pump for longer periods of time when running in normal filter mode. Does anyone have any information about the optimal flow rate for backwashing (per sq/ft)? I can find the maximum flow rate recommended, but that doesn't tell we what is best. I would assume that backwashing at a low flow rate will not be as effective at lifting the debris off the top of the sand. I would also assume that pushing too much water through the filter when backwashing would tend to begin carrying sand up and out with the water. If it makes any difference, I will be using Zeobrite as a sand alternative in this filter.

Thanks!

 

[duraleigh]

Hi, Tom,

I've got one of those big, big sand filters that suggested pea gravel and then sand (about 1/3 gravel then 2/3 sand up to the freeboard). I chose to put in all sand after talking to a few folks and have had no issues. I understand the theory, but doubt the benefit is very tangible......particularly with zeobrite since it's so much less dense.

If your freeboard (space between the top of the sand and the top of the filter) is correct, you will have little, if any loss during backwash. Backwashing on high seems much more logical to me and I would question the effectiveness of low speed to actually "lift" the dirt out of the sand. The filter tech support folks may have a more definitive opinion.