PSI to Backwash a DE Filter?

[Shifty]

When should you backwash a DE Filter? I have seen on this forum 2 different references of when to backwash a DE Filter.

1. When PSI rises by 8, or
2. When PSI is 8-10 over the "clean" setting on the PSI gauge.

Which is correct?

I am operating under the guidance of #2 above. Currently my PSI gauge is around 18psi. According to my gauge, I would be due to backwash around 28-30psi.

Here is a link to what my PSI gauge looks like (http://i22.ebayimg.com/02/i/000/a2/9c/fda2_1_sbl.JPG).

[famousdavis]

I was about to ask the same question, Shifty. I hope one of the DE filter experts can expertly answer your question. I'm not sure what the difference is between your #1 and #2, though, since #1 is relative to something -- but what is that something? If it's not relative to the clean setting on the PSI gauge, then was is the rise relative to?

I've flushed my DE filter sooner than 8-10lbs, though. When it rises to 5-6lbs, I'm ready to flush it because the water circulation is noticeably lower than when it's freshly flushed, and I'd have to run the variable speed pump at a higher rpm to get the same filtering effect (and that increases my energy bill). So, to keep the circulation at its optimum and my power bill down, and to keep the crystal clear appearance of the water, I flush my DE filter when it's 5-6 lbs above the "clean" setting. It only costs me a few dollars of DE powder, and that's it. In my one year of pool ownership, my experience is that it takes about five months between backwashings this way.

[Watermom]

bumping this back up

[mas985]

When the pressure in the filter rises, flow rate in the filter decreases so skimming and general cleaning are going to suffer not to mention efficiency. I don't particularly like the manufactures one size fits all 8-10 PSI rise specification because it does not take into account the starting pressure of the filter. If the filter normally runs at 10 PSI and you allow the pressure to rise to 20 PSI before cleaning, I can almost guarantee that the flow rate will decrease substantially. However, if the filter pressure is normally at 25 PSI with a high HP pump, it may never be possible to get to 35 PSI (max head). So as a compromise, I think up to a 25% rise is reasonable but also check the returns to make sure you are getting decent flow rate out of the pump.

[waste]

When the pressure in the filter rises, flow rate in the filter decreases so skimming and general cleaning are going to suffer not to mention efficiency. I don't particularly like the manufactures one size fits all 8-10 PSI rise specification because it does not take into account the starting pressure of the filter. If the filter normally runs at 10 PSI and you allow the pressure to rise to 20 PSI before cleaning, I can almost guarantee that the flow rate will decrease substantially. However, if the filter pressure is normally at 25 PSI with a high HP pump, it may never be possible to get to 35 PSI (max head). So as a compromise, I think up to a 25% rise is reasonable but also check the returns to make sure you are getting decent flow rate out of the pump.

THANK YOU, MARK!!

As you know, I've been giving DE filter care info (like [url=http://www.poolforum.com/pf2/showthread.php?9189-cleaning-a-DE-filter] the info in post #2[url]) for years and never thought about systems that start with a PSI of > 12.

It never occurred to me that any pool would have it's baseline PSI higher than that, because none of the pools I've built/ worked on ever did. I think your 25% is a very good way of telling when the filter needs be cleaned. (Waterbear advises a breakdown of the filter and manual cleaning every time it needs to be backwashed and some folks, with a starting PSI of 8 -12, backwash when there is a 3-5 lb increase - doing either of those things negates my standard recommendation of adding 80% of the start-up amount of DE... I guess I need to modify my stickied advice to accommodate this)

This thread is a perfect example of why I come here, I keep adding to my knowledge/ understanding of pools and, as a benefit, get to help some folks