DE filter, no backwashing required?

[DoAsFan]

Hello all,

I'm a new pool owner. I had a pool inspection done and they noted in the report that my filter is a "Premier DE no backwash type." Looking for some guidance on whether to backwash or not. Of course the inspection folks want to me to fork out more money to come out and give me more info.

More background info that might be relevant: based on the construction docs I have, the pool was built in 1979, and the filter has 72 sqft of cleaning surface area. Some additional notes indicate 138 GPM flow rate (not sure if that's a pump number or a filter stat or something to do with the pool pipes).

Attached is a photo of the 30-year old filter cleaning instructions I inherited.

Thanks,
Ed

 

[chiefwej]

I would be very surprised if the valve setup doesn't provide for back flushing the filter. Even when you do a break-down cleaning of a filter, standard procedure is to backflush first. DE refill after break-down cleaning on most filters is about 1.25 lb/sq. ft. After a back flush its about 80% of full capacity or around 1 lb/sq. ft.

I don't know who wrote those instructions or how long ago, but never, ever put Vasoline on the O-rings (it will destroy them) and I don't know where you would find a two-pound coffee can these days. You can get a DE scoop that holds one pound at most pool stores though.

 

[CraigMW]

I would be very surprised if the valve setup doesn't provide for back flushing the filter. Even when you do a break-down cleaning of a filter, standard procedure is to backflush first. DE refill after break-down cleaning on most filters is about 1.25 lb/sq. ft. After a back flush its about 80% of full capacity or around 1 lb/sq. ft.

Wow, that sounds like a lot of DE. My SMBW2060 calls for 1 lb/ft^2. Do you mean .125 lb/ft^2?

 

[UnderWaterVanya]

I would be very surprised if the valve setup doesn't provide for back flushing the filter. Even when you do a break-down cleaning of a filter, standard procedure is to backflush first. DE refill after break-down cleaning on most filters is about 1.25 lb/sq. ft. After a back flush its about 80% of full capacity or around 1 lb/sq. ft.

Wow, that sounds like a lot of DE. My SMBW2060 calls for 1 lb/ft^2. Do you mean .125 lb/ft^2?

You are both confusing me. Did you mean 0.1lb/ft^2? If not then these filters use 70+ lbs of DE?

 

[chiefwej]

Sorry, I should have said .125 pound per square foot for break down cleaning and .1 pound for back flush.

Only off by a factor of ten.

So your filter should need about 9 lb. after break down and about 7 lb after back flush.

 

[DoAsFan]

Hello,

Thanks for the feedback on DE refill quantities. I'll get a scoop.

I'm waiting on a replacement o-ring for the pump strainer and ordered some Aladdin Magic Lube as well. In the meantime, I'm still researching how to backwash and breakdown the filter system.

1) Having trouble locating the pressure release. I'm under the impression that this should be somewhere on the filter, but no luck finding it. Aside from the inlet/outlet/gauge, no other openings.
2) Not lucky enough to have a multiport-type valve, so I'm wondering if the black square-shaped plug on the filter return pipe is where I would let out used D.E.. Maybe backwashing wasn't "in" during the late 70s?
3) Pressure gauge is terribly rusty. Can I just squirt WD40 all over the threads, twist it off, and replace with a ~$5 unit from Amazon or Home Depot?

I've included a shot of the gauge, the filter inlet and outlet, as well as an overview of the whole system. Hoping to break the filter down and do a deep clean this weekend!

Thanks!
Ed

 

[Qwaxalot]

That "butterfly" valve on the brass "T" that the pressure guage is hooked to is the pressure relief.

 

[UnderWaterVanya]

I found this article about the history of pool filtration - it's biased based on the source but there was some facinating info on both sand/gravel filters and the history of DE filters. It appears that suction side DE filtration did not generally use backwashing historically - but looking at how this is deployed that does not appear to be a suction side filter.

 

[Richard320]

Now I get to see a picture, I see why you have those instructions. There is no backwash valve plumbed in. It's not a big deal. I have a backwash valve, yet I'm not satisfied with how well it clears the grids. The last two times I've opened the filter after the prescribed two minute backwash and found more than the rule-of-thumb 20% stuck to the grids.

So I backwash to get rid of most, then open it, hose off the grids with the backwash valve open (no disassembly), close it back up and backwash a little longer until the water comes out clear. I did it the other day. Start to finish, including rolling out 100' of backwash hose, took about twenty minutes.

 

[DoAsFan]

I sprayed some WD-40 on the pressure gauge, the Tee connector, and the draincock (thanks for pointing that out, Qwaxalot!), and removed the entire rusty assembly. Bought a replacement 60 psi gauge from Leslie's, a new T and draincock, along with some Teflon tape. Putting it all back together tomorrow.

After removing the drain plug on the filter outlet pipe, I was able to lift the lid off of the filter. Inside I found the grids coated in what looks like peeling green paint. I'm assuming this is what a dirty/algaefied grid looks like. I plan to hose them off tomorrow. What's odd is that there appears to be one grid that's completely white. Looks like its clean.

Questions
1) Is it bad enough that I should go through the whole TSP + muriatic acid wash process this first time around?
2) Any reason why one grid looks relatively clean?
3) Can/should I switch to a DE substitute like FiberClear? Just considering a safer to handle/inhale product than DE.
4) If the previous owner left three partial bags/boxes of DE of different brands, can I mix freely? Does this stuff get stale? For example: KemTek DE mixed with PoolTime DE?

Thanks for all the good info!
Ed

 

[Richard320]

1) Is it bad enough that I should go through the whole TSP + muriatic acid wash process this first time around? If the grids feel rigid, I'd vote yes. If they flex and water goes through them easily when you hit it with the hose, probably not.
2) Any reason why one grid looks relatively clean? It probably split and was replaced
3) Can/should I switch to a DE substitute like FiberClear? Just considering a safer to handle/inhale product than DE.I did and I'm happy with the change. I can backflush onto the lawn and it will eventually break down. Haven't noticed anything good or bad after doing it twice, no smell, no dead grass, no especially vigorous grass, either.
4) If the previous owner left three partial bags/boxes of DE of different brands, can I mix freely? Does this stuff get stale? For example: KemTek DE mixed with PoolTime DE? You can mix it all just like you could mix two different brands of flour, or sugar, or sand. It doesn't go bad. It's already millions of years old, it's basically fossilized algae.

Thanks for all the good info!
Ed