DE Coming Through Main Drain

[DanF]

Hi,

I installed a new salt cell over the weekend, and that required cutting PVC from my filter to the return line. After doing so, I noticed DE coming up through the main drain.
I did a search here and most of the "DE in Main Drain" posts reported this happening when the pump shuts off. In my case no DE is ever visible upon pump shutoff; only when I cut the PVC.

Is this normal?

 

[Jimrahbe]

Dan,

I am not sure exactly what happened, but if you have water in your filter and then "open" the system, it can drain the filter back into your pool. This would take at least some of the DE with it.

You can do the same kind of thing by having the pump off and just opening the filter's air relief valve.

When you cut the PVC to install your new SWCG, did you have your valves closed to prevent your DE filter from draining back into the pool??

Thanks,

Jim R.

 

[DanF]

Hi Jim...I did not have any valves closed prior to cutting PVC. Which should I have closed? Only one I have is the backwash slide ("piston type").

 

[JamesW]

You should always have a check valve between the pump and DE filter.

 

[DanF]

Thanks @JamesW but I am not understanding how not having a check valve between the pump and the DE filter would have caused DE to flow to the main drains when I cut PVC at the return line after the filter. I don't ever get DE return upon pump shutoff.

When I cut the return pipe did that open the system and allow water/DE to flow from the filter back through the pump and down the suction lines?

 

[Jimrahbe]

When I cut the return pipe did that open the system and allow water/DE to flow from the filter back through the pump and down the suction lines?

Dan,

That is exactly what I suspect happened..

Jim R.

 

[Jimrahbe]

Dan,

Also keep in mind you now have an unknown amount of DE in your filter.. I recommend you backwash and add 80% of your normal DE load.

Thanks,

Jim R.

 

[DanF]

Dan,

That is exactly what I suspect happened..

Jim R.

So to prevent this I should have a check valve where the red arrow is in the attached?

Dan,

Also keep in mind you now have an unknown amount of DE in your filter.. I recommend you backwash and add 80% of your normal DE load.

Thanks,

Jim R.

Good point and I did think about that already. I need to do my semi-annual filter breakdown (spray off grids, hose down filter interior, lube O-rings) tomorrow so I will address that then.

 

[Jimrahbe]

Dan,

I like a manual 2-way valve so I can just shut it off when I want to isolate the pump for the filter. But a check valve will work also..

Either valve will allow you to open the pump lid without the filter draining back into your pool.

Thanks,

Jim R.

 

[DanF]

Thanks Jim. So you turn your manual valve off each time you open the pump lid?

 

[Jimrahbe]

So you turn your manual valve off each time you open the pump lid?

Yep... When I am done and the lid is back on, I turn the pump on, and as soon as it starts to pull water, I immediately open the valve. The advantage of a check valve is that you don't have to remember to open the valve.

Thanks,

Jim R.

 

[DanF]

Got it LOL! At my age I'm trying to reduce the number of "have to remembers"

 

[DanF]

OK so I'm taking apart the DE filter and I look closely at my water feature pump. Is that a check valve on it? Why would the PB put a check valve on a water feature pump but not a filter pump?

 

[Jimrahbe]

Dan,

To keep the water in the water feature from flowing back into the pump when off.. Unlike your filter your water feature is not a sealed system,

Thanks,

Jim R.

 

[DanF]

Unlike your filter your water feature is not a sealed system,

Now I'm more confused. If my filter is a sealed system why did DE flow through the main drain?

 

[JamesW]

If my filter is a sealed system why did DE flow through the main drain?

You broke the seal.

 

[Jimrahbe]

Dan,

As James says, you broke the "seal" when you removed the pump lid. Or cut the pipe..

Thanks,

Jim R.

 

[DanF]

OK - One last question: Attached is a pic of my newly installed, but not yet wired, SWG. In the absence of a check valve between the pump and filter, would taking out the cell for cleaning cause DE to flow back through the pump and main drain? Thanks again for all of your help.

 

[JamesW]

In the absence of a check valve between the pump and filter, would taking out the cell for cleaning cause DE to flow back through the pump and main drain?

Yes.

Note that taking the pump lid off will not usually cause DE to return to the pool because the seal loss is on the pump side. Breaking the seal on the return side will cause de to go back to the pool.

 

[DanF]

Thanks - I was wondering why I never saw DE in the pool after removing the pump lid but you cleared it up.