I've actually heard that most pre-filters don't do a whole lot to extend membrane life... At least, that's the impression I got from actual users when I was shopping around for my RO unit. It's sad to hear that Aqua-Safe's quality is going down - I got an Aqua-Safe rig with a four-gallon tank for less than $150, including shipping, and it works great. That was two years ago, though.
Interesting info on the permeate pump, Av... I might have to go pick one of those up this summer. Do you think that adding one of those could get my holding tank to actually retain its entire four gallon capacity? Right now, my next filter-related purchase is probably going to be a pump for the input, as I'm far from the local station and my pressure is super low. I want to have more water on hold and figured that buying another tank and further decreasing the pressure differential would probably be a waste of my money... a line pressurizer seemed like the best option. You wouldn't happen to know how these types of pumps typically stack up, do you?
~Joe
PS - Er, I know the prefilters serve some purpose... Large sediments can harm the membrane. I think the particulate filter is the key part, but you don't actually need the activated carbon and some of the other stages that are included... Come to think of it, ignore me and do your own research...
the holding tank capacity will not change as long as you still use the 60% auto shut off valve, it stops flow once pressure downstream of the membrane reaches 60% of pressure upstream of the membrane. This amount of diff is required so the pressure diff stays at a level high enough to work, otherwist the brine rate would keep increasing and the unit would never shut off.
with the permeate pump you can run a 90% ASO vavle due to the isolation of the tank from the membrane output, this increase in outlet pressure will increase the tanks usable volume
but you must understand how the captive air tank works, it is basically a hydropneumatic accumulator.. i know big words... but it has bladder in it that is surrounded by "air" under a low pressure... now fluid flows into the tank compressing this air untill the air pressure matches the fluid pressure... so the amount that the tank can hold depends on the relationship of the air precharge pressure as compared to the max membrane outlet pressure
in other words if you water pressure is low, the two will balance before the bladder has expanded to fill the void in the tank, but if the pressure is high in relation to the prechare pressure the bladder will fill untill the void inside the tank is more full, holding more if not all of the full volume possible (rated volume)
Personally, i am a big fan of good prefilters... I have seen the life of my membrane and DI beads increase, remember the output TDS quality of the membrane is directly proportional to the input TDS... so if my membrane has a 95% rejection ratio and my input TDS is 1000 at the membrane the output will be 50ppm, whereas if the input to the membrane is 100 TDS the same membrane would have an output of 5 TDS
if your pressure is low then nothing will work like it should and it will be very inefficent
chlorine will destroy the TFC membrane material, so activated carbon is very important... now there is a membrane type that is chlorine tolerant... hmmm seems like it is CFC but I dont remember, but these are not very common in our hobby, the post membrane carbon filter is there mainly to remove any VOC's and bad taste that may come from the bladder itself.. so while not technically required, it does serve a purpose as well
mine is an old aqua safe as well, and it is a shame, they no longer use the same high quality DI housing or flush valve
but they have to stay competitive with the others on ebay, so I cant blame them I guess
Joe, if you want good stuff... go to
spectrapure.com, they are the porche of RO... see what brands they have and look for less expensive source if they are too high
fry, the permeate pump requires no electricity, it is powered by the brine outlet flow (very slick engineering BTW)
Av