RogueRose - 29-9-2016 at 22:18
I was playing around with a 3" to 2" PVC adapter and tried fitting a standard water filter in the 2" end and found it was a perfect (yet very tight)
fit. This sparked an idea. These filters are available in a variety of pore sizes from 1 micron up to 40 and I've found at least 8 different
materials from which they are made and a number of different styles as to how they are formed:
Most filters are resistent to temps up to at least 180F but many are rated well above 212F and most are highly chemical resistant excluding some
specific chems.
I found that the 3" to 2" adapter fits almost perfectly inside a 4" PVC pipe (with maybe 1/32 clearance on each side). This can be remedied with PVC
filler (acetone or MEK with PVC dissolved in it) which bonds with the PVC on a molecular basis - PVC glues are based on this.
Here you can see how the 3" to 2" adapter fits inside a 4" pipe (schedule 40 - IDK if that makes a difference)
Here is the design I came up with, I'm sorry they are not more "professional" with computer graphics but I think the idea is portrayed well enough.
The top of the filter will need some kind of PVC (or other solid material epoxied to it/glued. I would make it able 1/4" smaller in diameter (so
1.75" diameter) so there is 1/8" space around the edge for glue to hold it to the filter
The 6" to 4" reducer is place just above the 3" to 2" adapter inside the 4" pipe. The 6" is needed because it is impossible to change the filter
inside a 4" pipe with adult size arms (and child arms are too short - you need to be able to put a lot of pressure on the filter to squeeze it into
the 2" opening).
A "clean out adapter", 6", is used at the top of a 2ft section of the 6" pipe. The screw-in top allows for an air/water tight seal and allows for a
pressurized setup. In this section, either in the screw-in cap or as high as possible on the pipe of clean out adapter (don't drill into threads)
there needs to be something to allow pressurized air to enter, possibly with a one-way valve. A simple hose barb can be used and an air compressor
can be attacked directly (use hose clamp to secure hose) and pressure can build up slowly. Another access hole, maybe 1/2" with a ball valve may be
beneficial to allow addition of fluids (and release pressure if needed) to the tank.
This is 2 filter units stacked on top of each other. the top should have a larger micron filter (5-10??) and the one below should be smaller micron
(1?). Both need to have the disc glued to the top of the filter to restrict fluid flow bypassing the filter.
Inside of both filters it is possible to fill it with activated carbon if that is desired. On the bottom of the filter, a cloth will need to be
epoxied/glued like the top disc. This will hold the AC in place and any fluids passing through the filter will be filtered again by the AC!.
To connect the top filter section to the bottom a threaded 4" PVC adapter MUST be used (unless anyone knows how to connect 2 pieces of 4" pvc in a
water/air tight manner under pressure - must be able to be unthreaded-disassembled). I haven't found these locally but have seen them online. Price
was about $8 and $6 (female and male respectively)
I've found that small air compressors used for air brushing works well for something like this. they produce a fairly high CFM but don't have the
high PSI. Mine will do up to 60PSI and does 2CFM with no struggle (seems more llke 2.3-2.4). These are available online for $30-50 for an
inexpensive "Central Pneumatic" brand (harbor freight brand??). A simple hose running from the compressor to an input at the top of the filter housing
will do wonders for pushing the liqiud through these filters.
I'm in the process of getting the parts so if anyone sees any major flaws in this then let me know. My biggest issues is that I would like to be able
to run 212+ degree liquids through it (like hot fats or oils at maybe 300F) PVC won't handle this. PVC is great for chemical resistance though. I
would like to be able to put some immersion heaters inside the filter housing to keep temps up, but IDK how well that would work (weakening the PVC)
I was considering using these:
10" diam housing
2" diam housing
Stainless steel housing - THIS WOULD BE GREAT if it is affordable!
[Edited on 30-9-2016 by RogueRose]
Dr.Bob - 30-9-2016 at 05:51
Not sure how you think that PVC is "great for chemical resistance", as it is terrible with most organics, and likely with fats and oils. Most PVC is
a mixture of PVC and plasticizers that make it leach out phthalates horribly to almost any solvent. Plus is will NOT handle higher pressures well,
especially when hot or leached with chemicals. If you want to filter a hot liquid safely, you need a metal housing and all metal hardware.
Especially a hot oil or fat which might be flammable at those temps. HDPE is much better at pressure and chemicals, but even it will not handle
temps of 300 F.
Not sure what you are trying to filter, but for example, the biofuels industry filters hot fats and oils, but they use hydraulic pumps and massive
filter assemblies which remove things like french fry particles from fryer oil. But filtering oils takes a lot of PSI, not sure if simple pneumatic
pressure will work well. This sounds like a more industrial process than most people here are doing, for those types of processes, the best
solution is to test things on smaller scales and then incrementally scale up, thus avoiding large messes. But no chemical engineer would use PVC
for any filtration, reaction, process, or chemistry, even for water, other than low pressure and cold temps. They likely sell a filter assembly for
deep fryers that might handle those conditions, look for that, as McD's and others likely use them, thus the price will be reasonable.
careysub - 30-9-2016 at 07:14
"unless anyone knows how to connect 2 pieces of 4" pvc in a water/air tight manner under pressure"
Ordinary solvent welding of the pipe end-to-end will do this. It creates a bond as strong as factory-made pipe. I've done this and tested the new
longer pipe with a heavy shear mechanical load and it held up as expected. (Obviously you should dress the ends carefully, and use fresh cement to get
the best bond.)
You can also bond reinforcement to the pipe with epoxy if you flame-treat the surface first. This is done by passing a propane torch flame over it so
that it loses its gloss and becomes dull, just takes a moment, the surface bonds are temporarily broken (also do this if you want to paint PVC).
Better chemical and temperature resistance can be had by using chlorinated PVC - CPVC at somewhat higher cost.
How much pressure were you planning to put into this? You if you are just filtering, I can't imagine more than a few psi would be involved, and the 4"
CPVC pipes are good for about 45 psi (schedule 40) and 65 psi (schedule 80) at 200 F.
RogueRose - 30-9-2016 at 10:54
I made a correction on the part about connectin the two 4" pipes together. This joint needs to be temporary in that it needs to be unscrewed or some
kind of compression connection. (I had an endcap with a 3/4" silicone plug on the end that when the cap was cinched down (4 point anchor on cap and
pipe) with a ratchet action, the seal was perfect up to 150 PSI with no problem. I don't see that working here though, so I need to find male/female
adapter.
In this pic, in the middle where the 2 pipes are separated, that is where the male and female threads need to be so the bottom can be taken off and
new filter put in and everything cleaned if needed. These 2 parts are a little difficult to find as well locally.
As far as chemical resistance and pressure and heat rating, CPVC is better but prices are unaffordable as it would cost almost 6-10x depending upon
piece (couldn't find many pieces over 2" anyway).
I'm planning on schedule 40. The 3" piece I have in hand has a 260PSI rating and I don't suspect I would get above 60 PSI and that would be brief
for flushing the filters.
As far as chemical resistance. I may have mis-spoken or misrepresented the intendd use. Most liquids will be water solutions
I have been using these charts as a guide. IDK if they are accurate or if they are misleading.
Plastics Resistance Chart 1
PVC Resistance Chart 2
I also plan on coating the pipe with a few coatings of spray PTFE which I have used on many other plastics and it did an excellent job in preventing
any type of pitting, staining, dissolving/abrading, etc with the solutions I am planning on using.
This isn't intended for solvent use - I should have said that.
If I could make this out of Stainless I would, I don't have that kind of scratch though..
careysub - 30-9-2016 at 11:30
PVC should do okay with common alcohols as well.
Using the U.S. Plastics website as a reference it appears that the price ratio of 4" Sch-40 PVC:CPVC is about 1:3, a lot more expensive for sure but
$80 for five feet is not sky-high.
Stainless steel pipe is available cut to length for about $25/ft:
http://www.onlinemetals.com/merchant.cfm?pid=920&step=4&...
$68 for 3 feet.
[Edited on 30-9-2016 by careysub]