Can you double up sock filters?

I was thinking something like a 25 micron sock filter inside a 5 micron filter. I could filter one time and get a final 5 micron product.

they sell these at mcmaster-carr

I actually use a three socks inside one another. They are all the same (1 micron), but the inner-most one has been washed several times, the middle one has been washed once, and the outer one has never been washed. This allows the benefit of being able to wash them without worrying about hurting their filtering efficiency.

does washing filters hurt their micron rating?

I already use 25 & 5 micron bags. I'm using two seperate filter drums. I was thinking about a sock-in-a-sock and use only one drum.

I could filter once and achive 5 micron final rating.

I am not sure how washing affects their rating. That lack of knowledge is why I do what I do. I do know the efficiency of the filters isn't all that great. I have a Vormax as the last step in my prefiltering process, and when I was using only one 1-micron bag, I was changing the spin-on every 75-100 gallons. Since going to my 3-bag setup, I change the Vormax spin-on about every 250-300 gallons. My prefiltering may be overkill, but I don't remember when I changed the Racor in the car; vacuum stays at a constant 1-2 inches of mercury.

I found that synthetic material bag filters ability to filter reliably was compromised by washing in a machine. Feeling that the agitation might be part of the problem I tried washing in a dishwasher at various temperatures. They seemed to be less compromised by this method of washing. The synthetic filters that were of a woven clothlike material seemd to be a bit more durable than the synthetic felt material type filters.

I found that unsupported their filt3ering ability was compromised by the stretching of the filters due to internal pressure. But by using an older filter on the OUTSIDE of the new filter the new filter fibers seem to be supported and so keep their filtering ability uncompromised. Essentially the inner filter bag is doing all the filtering..the outer bag is mearly for support.

I found that I could easily and cheaply make my own non-synthetic material 10 micron filter bags for a few bucks. These seem totally uneffected by washing and so can be used over and over.

If you have an older filter on the inside, it holds most of the oil, therefore most of the pressure. Since the oil that goes through that for the most part goes quickly through the new filter, there is little weight placed on the outer bag. Of course this does assume that both bags are supported by their ring, not by each other.

I see your point Habenero...but I submit:

The synthetic material tends to stretch a bit when used. So placing a used and therefor slightly larger filter on the inside does little to actually support the new filter on the outside and prevent its fibers from being pulled further apart..compromising its filtering ability. The pressure exerted on the inside filter is directly transferred to the outer filter as it presses outward on the new one.

On the other hand placing the new (and slightly smaller)filter on the inside of the previously used (but cleaned) bag filter allows the inner bag to be somewhat supported by the outer one. Optimumly an unused larger micron rated (but asme phisical dimension) bag filter should be placed on the outside so all it provides is support and not filtering. This means that it will never have to be cleaned and therefor will remain closer to the original (unstretched) size. This will provide the best possible support of the inner bag filter and help prevent its fitering ability from being compromised by the stretching which takes place due to the weight of the oil inside of it.

These filters can hold nearly 4 gallons of oil..which translates to around 30#. The support ring holds the filter "up"..but does nothing to prevent "ballooning" of the filter itself. While this cannot be completely prevented getting the outer filter to "take some of the strain" helps some.

quote:

---

Originally posted by danalinscott:
snip...The pressure exerted on the inside filter is directly transferred to the outer filter as it presses outward on the new one.

---

I think we are missing each others' points. The way my filters are situated, the inner filter sits roughly 1/2" higher than the outer filter. Sure they touch on the sides a bit, but at the bottom, the inner filter never touches the outer filter, so there can be no pressure exerted.

I don't know about the 4 gallon figure, but it is true the weight of the oil is significant on the filter. But, in my set-up, the inner filter is really the rate-limiting step. Even though it has been washed and is probably letting through slightly larger particles, it only passes oil at a slow rate. Then, this oil that is already 90% cleaned, passes through the outer filter (actually filters in my case since I use three socks) more quickly. So, most of the weight of the oil is being applied to the inner filter, which because it is not physically touching the outer filter, cannot transfer this force to it. Therefore, the outer filter is only being affected by the weight of the few cups of oil present in it at any given time.

Now all this being said, if one were only supporting the outer filter and simply had the inner filter sitting inside that, then your scenario would come into play.

Habenero,

How do you keep the inner sock from touching the other sock filters? Is it a smaller size than the outer sock?

I do sometimes use a smaller inner filter, since I have a few from earlier experiments. But, even the ones that are the same size only touch on the sides, not on the bottom. The ring of the inner bag sits on top of the ring of the outer bag, thus making it sit about 1/2" higher than the inner bag.

Hab,
It is the sides of the filter touching that I was reffering to when i said that the filters "balloon" out and so directly transfer the pressure from the inner filter to the outer one..stretching the outer filters fibers.

Maybe it is a case of different filter materials, but the ones I have don't balloon out much at all. Of course they do puff up a bit, but I would say they sag more than puff out. The polyester felt is pretty stout material and really doesn't deform much at all.

At any rate, I think you can pretty much flip a coin either way you situate your filters. Since most are using a single sock anyway, an additional filter either on the inside or outside is bound to add some filtering efficiency. The difference in orientation we are talking about probably accounts for less than .5% filtering efficiency either way, so it is sort of a moot point.

Yeah..I agree.
Filtering with two sock filters is probalby better than one no matter how they are arranged. But....These bags do stretch both vertically (due to the weight of the wvo inside them) and horizontally (due to the pressure this confined weight exerts).

Adding heat (for cleaning or wvo thinning purposes) exacerbates the deformation of synthetic filter bags. If you are filtering using 2 micron bags this is probably not significant. But if you are using 10 micron synthetic bag filters I believe it is.

Regardless..I would not use any wvo filtered with any bag filter without first running it through a "polishing" filter to avoid having my vehicles filters clog with missed particulates.

quote:

---

Originally posted by danalinscott:
...Regardless..I would not use any wvo filtered with any bag filter without first running it through a "polishing" filter to avoid having my vehicles filters clog with missed particulates.

---

I whole-heartedly agree. For me the bags are just rough filters no matter what the rating is.

Hi Guys

I've been filtering WVO through sand (after settling) and it works a treat. Bit slow though and I can't gaurantee what particulate size it filters down to...

quote:

---

Originally posted by danalinscott:
I found that I could easily and cheaply make my own non-synthetic material 10 micron filter bags for a few bucks.

---

How did you arrive at the 10 micron figure when rating your bags?

quote:

---

Originally posted by Uber-veg:
Hi Guys

I've been filtering WVO through sand (after settling) and it works a treat. Bit slow though and I can't gaurantee what particulate size it filters down to...

---

Uber do you filter "up" thru the sand or "down" through the sand?

You filter up by introducing the oil at the bottom of your filtering vessel. The oil then moves up through the sand leaving crud in the sand. This technique has the bonus that clogs tend to self clear as pressure builds up the sand and filtrate will move in a turbulent fashion. At some point well above the sand you have an outlet port that your oil is allowed out through. Viola sand filtered oil.

In my limited understanding of pool and municipal water filters this is how they operate.

Glenn
PS My attempt at a downflow sand-filter was a nasty mess. Search for "The contraption" for more on the mess and how not to make it.

quote:

---

quote:
--------------------------------------------------------------------------------
Originally posted by danalinscott:
I found that I could easily and cheaply make my own non-synthetic material 10 micron filter bags for a few bucks.
--------------------------------------------------------------------------------



How did you arrive at the 10 micron figure when rating your bags?

---

I filtered the (prefiltered) wvo through 10 micron rated filter paper. Since no particulates showed up on the filters of "known" 10 micron rating it logically followed that the prefilters were filtering to the same or finer size. Since the initial tests have run up to a thousand gallons of prefiltered wvo through a single fuel filter rated at 10 microns and had no symptoms of particulate accumulation. This verified to me that the prefilters were of the same or finer "micron rating".