DE draining back to pool with pump off

[a_t]

Hi,

I just replaced my old 36 sq. ft. DE filter with a new 48 sq. ft. filter. I kept the same 3/4 HP Hayward Max-Flo pump, but replaced all of the plumbing. I've got a couple of questions, but here are the pictures of the old and the new:

Question 1:
When I used to open the old filter for cleaning, all DE was stuck to filter grids and there was almost no free DE in the filter. With the new filter, only about top 1/4 of the grids has a layer of DE, and the rest is at the bottom of the filter. Is this OK? Does it mean that the pump is under-powered for this size of filter? All the plumbing in 1.5".

Question 2:
The pump has been off. This morning I opened the air bleeder valve on top of the filter and a cloud of DE came out of the main drain and the skimmer. I do not have a check valve between the pump and the filter. Is this DE draining back to the pool the expected behavior without a check valve, or should DE not drain back even without the valve, meaning there is something else wrong with my setup? Is the solution to put in a check valve? Does this problem also have something to do with question #1?

Thanks!

 

[jblizzle]

1: It probably just means the DE is falling off when you drain the filter to open it. You pump should be plenty big.

2: I see nothing wrong with your setup. When you open the bleed valve, you are allowing air in and the water can drain out of the filter which would carry some DE backwards like you see. Oddly, I have never noticed this to be a problem. A check valve between the pump and filter would stop that, but they are usually not needed. If you modify your 3-way, you could close off the pipe to the pump before opening the filter.

 

[JohnT]

If you are accumulating air in the filter, it can push DE backwards out of the filter when the pump shuts off.

 

[a_t]

Thanks for your response!

1: It probably just means the DE is falling off when you drain the filter to open it. You pump should be plenty big.

I was just surprised to see this because I was used to grids being fully covered in the old filter. I wonder if the the bottom 3/4 of DE gets washed off because return plumbing in the new filter is much higher than in the old filter. So when I open the air bleeder on the filter, water "rushes" back in from the high return pipe and washes off the DE.

2: I see nothing wrong with your setup. When you open the bleed valve, you are allowing air in and the water can drain out of the filter which would carry some DE backwards like you see. Oddly, I have never noticed this to be a problem. A check valve between the pump and filter would stop that, but they are usually not needed. If you modify your 3-way, you could close off the pipe to the pump before opening the filter.

I think it may be a problem in two ways. First, the amount of DE washed back is significant, so after a couple of these clouds in the pool I may not have enough DE left in the filter. Second, whatever DE gets back to the pool will settle on the bottom and require more vacuuming/filtering. I guess the right thing to do is to install the check valve.

 

[jblizzle]

Like I said, I have never seen a need for a check valve between the pump and filter, but it would stop the DE.