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Permeate pumps?

  • Thread starter Zero
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I wasn't sure where to put this but does anyone know about Permeate pumps?
I have had one for a while now and am just reading up on them.
It says on some sites I don't need a auto shutoff valve because the pump will stop when the tank reaches line pressure.
Can someone who knows anything about R/O systems chime in?
It would be nice to take out the auto shutoff valve but I don't want to waste water.
I don't know much about them but I can pull one apart and put it back together.
Also, I have to replace the prefilters every 2-3 months. Is that normal???
Typically a unit with a captive air tank and no permeate pump will run a 60% ASO valve, a system with a captive air tank and permeate pump will run a 90% ASO

can you run a system with a captive air tank, permeate pump and no shut off... well in theory yes. However, it will cycle whenever any pressure differential builds up.

I mean if the pressure coming to the house fluctuates up (as is typical during certain parts of the day) you will hear the permeate pump start running. Also it will run whenever any RO water is used.

So can you, yes... would I?... no, the 90% valve will keep the system from running until the permeate pressure drops to 90% of inlet. This gives you a 10% deadband to prevent excessive cycling of the system and pump.

3 months for prefilters?.... owie, are they getting that stopped up?.... what are you using for a metric to know when to change?.... I would recommend checking for a 5 or 10psi pressure drop.

If they meet that metric then not much you can do, with the exception of installing a single large prefilter to remove most of the junk before it hits the RO prefilters. A sediment trap is another option and its a good one, but that would require some plumping skills. If interested in that option hollar and ill try to help ya with the design.

Hope this helps,

---------- Post added at 01:13 PM ---------- Previous post was at 12:18 PM ----------

ummm i should have a good used 60% ASO if you need it ;)

the isse with using a 60% ASO with a permeate is a reduced maximum permeate pressure, but its perfectly fine operationally

just hollar and its yours mate,
Thanks Av8tor1,
I Upgraded to the 90% shutoff valve a year or so ago. I think it was you who recommended it.
There must be a lot of sediment in my water, I know the 1st prefilter turns a nice rust color quickly.
The weird thing is our tap water runs at under 50ppm. I changed to 30 10 10 micron prefilters because the 10 5 1 that was recommended plugged up quick. I measure when to change the filters by how long it takes to get my plant, coffee, and drinking water. I don't want to wait 6hrs for 2-3 gallons of water:) I still get 0-1ppm out of the R/O unit which is better then most I have heard.
Is this setup right? Doesn't look right now that I look at this pic. The permeate pump runs as soon as water is drawn.
old pic of what my filter looks like after 2-3 months. Those filters should be pure white.
Thanks for the input, I'm pretty brain dead most of the time.
Forgive me for asking a silly question but Im assuming the captive air tank is not in the pic but is still installed correct?
I have to be honest, your comment about taking 6 hrs to get 2-3gal of water and not seeing it the pic makes me wonder....

Zero, here is mine...

my RO/DI/PP/90% system:
blue = permeate
blk = prefiltered water
yellow = brine
red = fresh water inlet
white = bladder tank
clear = inlet and outlets to system


you should get much longer prefilter life when using a permeate pump... my inlet TDS is around 100ppm and I get 6 months easily, could probably go 9months if I really had too

Something just doesnt sound right... can you trace your lines down compared to my images and verify proper plumbing?

Permeate pump owner's manual with installation schematic: http://spectrapure.com/manuals/PRINTER_FRIENDLY/PPRFK-MANUAL.pdf

Thanks for the diagram and info Av8tor1.
I think it's hooked up correctly. The captive air tank is hooked up, I just run It dry then have to wait. I go through a lot of water. I never measured, but maybe 6-8 gallons a day. It's just sometimes I need all that water quickly. If I have neglected to water my plants for a couple of days I need 8-10 gallons and I don't want to spend hours doing it. How much water do you get out of your captive air tank when it's full? I get about 2 gallons. If I had a house instead of an apartment I would have a larger captive air tank.
I get about 2.5-2.75 gallons from mine

Is yours a 100gpd?...

Measure the brine rate for me.
Disconnect the waste water hose and run it into a pan. Then close the valve to the captive air tank (we don't want it to influence our test)
Now run it till you get a couple cups of RO water and compare this amount to the amount of brine. It should be around 3 or 4 parts brine to 1 part RO permeate.
As you perform the test, also measure how long it took so we can calculate the oz per minute.

Zero, Inlet pressure and water temps play a major role in all this., the 100gpd rating is based upon 60psi and 77f water at the membrane inlet, so its not a real world rating.
If the ratio is greater then 4:1 then we have a problem and need to take some pressure measurements.
It actually sounds like your inlet pressure might be on the low side. This would also explain why the finer grade of filter caused you premature problems
But I don't want to jump to that conclusion until we perform the proper diagnostic steps.

Do you have a pressure gauge?


---------- Post added at 02:23 PM ---------- Previous post was at 02:10 PM ----------

Here is a copy and paste form a previous thread where I was helping another cp'er

* bladder tank must be isolated from system during brine ratio measurements
* hydraulically operated automatic shut off valves will typically shut off the inlet to the membrane when the outlet pressure reaches 60% of inlet pressure
* In a real world system getting 85% of rated flow is about the maximum attainable**
* at 85% a 100gpd system should produce about 7.5oz/minute (bladder isolated)
* In bladder tank systems, membrane efficiency drops proportionally as the bladder tank fills. This is due to backpressure on the membrane outlet.***

** inlet pressure, water temperature and TDS will have a major effect on membrane output
(TFC membranes are usually rated at 77 degrees Fahrenheit @60psig and for every 1 degree drop, production drops 1.4% (57f water would reduce efficiency by 28%))

*** This drop in efficiency can be prevented by the use of a permeate pump and 90% automatic shut off valve. The permeate pump isolates the membrane from this build up in back pressure. Since the pressure differential across the membrane now remains constant, membrane efficiency also remains constant resulting in greatly improved recovery rates. This isolation also allows us to replace the 60% ASO valve with a 90% ASO thereby utilizing more of the bladder capacity and increasing output pressure. These modifications will result in a 60-80% drop in water consumption and brine output. In addition, this drop in water consumption also results in a proportional increase in prefilter life. A nice, simple and fairly inexpensive mod for any system using a bladder accumulator tank.
OK, I did the test and I'm disgusted by the amount of waste water.


1 cup R/O
14 cups brine
9m10s time
tap temp is 39F
why is it this bad and what can I do to remedy it?
owie.... well this sure explains why your prefilters are dying at 3 months and the terrible recovery rates. To be honest this is as bad as Ive ever heard of.

Zero, its probably inlet pressure issues mate, but we have to do this systematically to be sure. Do you have access to pressure gauge?

no pressure gauge. Where would I get one?
  • #10
Lowes has some that are under ten bucks in the water well supply section. You will then need to get it tee'ed into your system. Just sticking a gauge on the line isnt a valid test. We have to measure pressures dynamically (while the RO unit is running) We need to make sure that pressure is staying above 40 psig while running... 50 would be better, 60 would be ideal.

I imagine you hear your permeate pump running for hours after you empty your captive air tanks. If you didnt have the permeate pump things would be much worse Z... the unit would probably never shut off and the brine rate would get even worse then it is as the tank filled.

Look at my pics, see how i tee'ed the gauge into the inlet line, that is your next test point.

If it passes that test then we need to move the gauge to the membrane inlet and dynamically test pressure there. If it passes that test then the membrane becomes suspect

But one step at a time, systematic and by the numbers.... no other way to properly do it

after thought: has it ever worked correctly?..... just wanting to verify that there is a flow restrictor installed in the brine outlet of the membrane. If it were missing we would have these same symptoms... Ive never seen one missing before... but there's always a first time :p

(labeled G in my images, mine is a dual purpose flow restrictor and flush valve)
(its also shown in that permeate pump owner's manual i linked to above

This appears to be your flow restrictor, just verify its plumped correctly into the system per my pics and the manual diagrams, also please verify for me that it is the one that was matched to your membrane's flow rating.