Saturday, September 22, 2007

Scam: reverse osmosis permeate pump and valve

Not exactly scam, but depends on who and how they sell it. The permeate pump is certified, made of harmless material, and won't fall apart, but it is the magic bullet as claimed in the manufacturer's Aquatec website? No. But since they only sell it to distributors, they give you no specification and they are not responsible how you use it. But now these companies know that nothing can stop people selling things to individuals on eBay, they are a bit careful on their website, in order not to develop a scandal.

Many pumps are sold to retrofit existing systems. But notice the 75 psi feed input on the main diagram on their website. If you haven't got that pressure, it very doubtful it will work well. And if you got all that pressure, it's doubtful if you need a pump to get good results.

Standard main water pressure depends on water district, but should be 50 psi, which is the value for sprinkler specification. You may get higher pressure if you live uphills in individual houses, where the water pressure gradually decrease downhills to 50 psi for houses at the bottom. In this case you need a pressure regulator, which is usually factory preset to 50 to 60 psi, with 75 psi as the absolute rating. So basically, now that the permeate pump isn't new anymore, Aquatec is basically saying you need a booster pump without admitting it. A booster pump cost twice as much and gives you a lot of improvement if your feed is just 50 psi. It's crazy if you use a booster pump plus a permeate pump. Since I have 75 psi without the need for a booster pump, I'm OK. It wouldn't work well for 60 psi, and I can prove it.

When the tank is empty, that is, no back pressure to the membrane, the membrane sees the full pressure of about 70 psi. The pump is supposed to maintain the back pressure to at most a few psi so the full 70 psi pressure is maintained at all times. With the right flow restrictor, there should be enough pressure and flow in the brine/concentrate to do that. But I found out that the recovery rate have to be high at about 25%. Which means that the drinking water to waste water ratio is 1:3. This is far from the usual 1:4, or 20%, and far from the specified Filmtec membrane recovery of 15%.

But all is not lost. At 70 psi, even 25% recovery gives 98% stable rejection, which is the same specified rejection at 50 psi and 15% recovery. So with a virtual booster pump, and a permeate pump, I can't get better rejection but I waste half the water, 1:3 recovery instead of 1:6 recovery.

It won't work if you don't have 75 psi main feed. Say at 60 psi feed, you have about 50 psi across the membrane, and clearly at this pressure, you need 15% recovery to achieve anywhere near 98% rejection. 25% recovery is far off.

It's doubtful if you need any pump when you have 75 psi pressure. A 75 gpd membrane becomes 110 gpd which is a hell lot of water. But since the pressure is constant across the membrane, it's easy to design your system, and the performance is guaranteed under all circumstances. In other words, peace of mind.

In pumpless systems, basically the water is excellent when the tank is empty. Then the water tend to get worse as the tank fills up, or you waste a lot more water without realizing it, that's what Aquatec is trying to market their pumps. With typical usage, the system works most often when only a few cup or a kettle of water is being drawn from the tank. The water is worse or wasting most water when the pressure across the membrane is often 50% to 33% of an empty tank.

Actually I would like to write software to design residential systems. Dow has free software but far too complex and did not give out parameters for the residential membranes. So I couldn't do anything but to use 75 psi main pressure. The pressure is constant and everything is constant so it's easy to design.

And now the cutoff valve. It's not cheap at 1/3 of the pump price. But does it worth it? Nobody claims that it's necessary but say enough that you will buy it. I was surprised to find out that the valve don't cutoff at 90%, but about the same as the old valves about 66%. I talked to the distributors and manufacturer and it seems that they are well prepared. The distributor send me over to the manufacturer, who promise to test it and replace it if it's defective. But I am not to expect 90%, but 85% depending on pressure.

I almost sent it off when I realized that now the cutoff pressure of my tank will be the main pressure of most people, at 50 psi. It will be crazy to increase that to 65 psi. I don't need that and the pump may not work at that pressure. Also, the valve turn back on at 30 psi, giving 20 psi of hysteresis so the system won't turn on and off whenever people drawn a glass of water or a kettle of water. I don't know if my old valve do that. But since the new valve has JG connectors that are easy for me to measure things, and that the tubings are fitted already, I rather not go back to the old one.

Previously I have doubts about measuring pressure when water is flowing. But I find that it's very accurate, the dynamic pressure into the tank equals exactly the static pressure when the tank is isolated. After all, what else can it be? Now I left the pressure gauge dangling in a T piece somewhere in the water path. And since I needed a tank shutoff valve as an adapter for the standard gauge, I can shut off the valve so the gauge isn't in contact with potable water when not in use.

27 comments:

Derrick said...

Thanks for the article on ro permeate pumps. I was interesting in buying one after reading its features. I wanted something that would maximize my faucet flow and if it made the whole contraption work better... then bonus. I've got 65psi water pressure in my house.

The Player said...

You're welcomed. 60 will be bad. 65 may be OK, depending how much % rejection you want when the tank is empty and when it's almost full. Probably you need to experiment with different flow regulators. If the flow is too large, the pump cannot build up enough pressure to work.

Anonymous said...

I'm a water treatment dealer and I use these pumps all the time on private wells (40-60psi) and they do what they claim: waste less water, boost pressure in the tank, and they usually have a 20% recovery. I don't think they are intended for an electric booster system. This product is NOT A SCAM. They may not do a whole lot on city water that is typically 60psi but at least they would waste less water and unload the backpressure on the membrane. There was a manufacturer that made 90% shutoff valves but I haven't found any else that makes them. I usually don't use a shutoff switch unless the pump fails.

The Player said...

Well, the heading is a little sensational. I agree that the pump will bring significant improvements compared to without one. Practically you cannot get close to 98% rejection if you don't have 70 psi, that the filmtec membrane is capable of. But residential osmosis systems starts from 85% rejection at the low end. A few percentage below 98 will be very easy to achieve.

Anonymous said...

I have a permeate pump on a 40-50 psi shallow well pump. It works as advertised. Without it, my 4 gal tank only holds 5 qts, with it close to 4 gal. Recovery time is much quicker too. Faucet pressure is higher, rejection rate is 98% with a fairly new 50gpd filmtec membrane. I think you may have done some calculations wrong. This product is most useful at around 50psi, and tends to top off your tank at whatever the top system pressure is.

Anonymous said...

PS I use the 90% shutoff valve. It is still avail. for $20. Highly recommended.

The Player said...

Well, you have to ask them why they put 75 psi at the pump website.

The only calculation I can do is the flow restrictor. The standard one suitable for 15%/20% recovery does not give enough pressure within the system to work. Water is draining too fast for any pressure to build up. I had to increase the recovery rate by using an older flow restrictor.

Oh yes, I forgot that the alternative is to lower the input pressure, because the 15%/20% recovery is specified at 50 psi.

The old Filmtec data sheet used to have a few interdependent curves so you can really do some calculations. Now without the curves, you don't even know what restrictor to use when you use a booster pump in front.

As for the valve, I did use the 90% cut-off valve, but far off from 90%. I didn't return it to the manufacture as my tank input is already 50 psi because my water pressure is 75 psi.

With all the improvements now, my rant should have been that previously, we are sold lots of crap for years(without pump and higher cut-off valve).

Anonymous said...

I have been using one for years on a cistern and a well and they do work very well. They are not a scam, you have not done your numbers right somewhere.

The Player said...

The whole point is how well is well. Filmtech doesn't give you enough info to design it on paper other than at a single point of 50 psi. For individual users, you don't have time and resources to design by try and error and measurement.

Anonymous said...

I use one on my system on city water. After using the same system for a while without it, I can say it definately improves tank refill times and fills the tank fuller using the 90% auto shut off. As mentioned already, they run about $20 from various online suppliers. Not sure about rejection rates, as I have not monitored those closely. As far as being a scam, in my experience most manufacturers tout great features in big bold ads, and hide the fact that to get those results you have to have "perfect" conditions, which very few of us have. You just need to find a dealer who values honesty and helping the customer over trying to make a quick sell.

Anonymous said...

Its Not a scam. I was without a permeate pump for 9 years and always had low pressure issues at the faucet. Installed one today and LOVE IT! its like my refrigerator works again! Helps a TON!

Anonymous said...

Just installed a Watts 50GPD system. It tends to run a long time ors) to top off, all the while rejecting about a liter/minute. makes so much noise that it can be heard all over the house. Production is about 100 ml/min, which is about right. Watts tells me to install a booster pump, as mains pressure is only 45 psi. Fresh Water Systems, where I bought the system, sold me an inline flow restricter, supposedly better that the one now inserted in the membrane cartridge reject port. It hasn't arrived yet. Others have told me to try the permeate pump. Question: will a permeate pump work at 45 psi mains, and if it does will it help?

TIA

The Player said...

One cause for noise is the flow restrictor value too large. Since a typical membrane give you one design point at 50 psi, if one variable changes, all design value could change.

(The other is of course the air gap faucet. I got rid of it once and for all and use a one-way valve instead.)

Pumps always help. Booster pumps are more expensive because of main pressure and electricity components. You can improve water quality and save water at the same time.

The beauty of permeate pump is that the water quality (and other variables) do not depend on how many water in your RO tank. When your tank is full, without permeate pump, you have only about 16 psi across your membrane instead of 50, when the tank is full. So the water quality is actually an average between clean water and not so clean water.

If you don't have design curves of the membrane, the number that counts is the TDS meter reading.

Anonymous said...

I hate to tell you this, but you don't even understand how the pump works. I don't know where the 75 psi comes from. The pump is designed to enhance low pressure systems. That's what it's for!

The Player said...

The 75 PSI came from the manufacturer's website.

Gene said...

Then you misunderstood the website. On low water applications, with 40 to 50 psi coming into the unit, the permeate pump is especially valuable.

The Player said...

Oh yes, I'm not really ranting about the pump. It always improve. I'm ranting about how poor all systems are before the pump. They don't tell how bad it is until they solve the problem.

FlaRick said...

The Permeate ERP 1000 pump, is
built for only 1 year 6 months
usage. I have now just ordered
a 24VDC boostpumpfor my RO water
system supply. I have well water
and 30 to 50psi supply. There fore
need the boosting of pressure.
Like the other comments input,
no way top get hold of the builder.
But it last for the warty., 1 yr., time frame. Hopefully the DC pump will last for years and years.
I WOULD NOT recommend Permeate
mech., pumps to any one!!!!
My original one was MFG Germany,
last 3 had USA on it. All of them fail
down the road way to quickly$$$$

The Player said...

Mine is still going strong. I believe I had it well before 9/2007.

pszemol said...

I noticed you mention 75PSI but the Filmtec membrane designed for residential system are build for the target 50PSI.
See this -http://www.dow.com/PublishedLiterature/dh_0475/0901b803804753ac.pdf

I rent appartment in west suburbs of Chicago and the measured pressure of the tap water hoovers around 42-44PSI. Close to 50PSI but far from 75PSI.

Should I get the permeate pump or I do not need one? I have 50gpd so I was thinking about getting smaller permeate pump designed for smaller membranes (like ERP500 instead of ERP1000).

Thanks!

The Player said...

Just because the filmtec is specified at 50 psi. (It works better at higher pressures.) The pump company just wanted to avoid legal troubles by writing down 75 psi on their website. There are pressure drops at the prefilters, a few to 10 psi. If you have 75 psi main pressure, it's easy to get 50 at the membrane. Standard main pressure is only 50 so anything near it is good pressure. My title was just to attract attention. You always get better results with a permeate pump. Before that the cheap filters are a joke. On average the rejection may be good, but a lot more garbage passes through when the tank is almost full, compared to when the tank is empty. A pump will make that even.

At my time, the small pump is supposed to be quiet while the big pump has the typical click. It's annoying if you have to sleep near the kitchen without a door, if the pump is under the sink. Pets will suffer too.

NameBrandFaucets said...

As we all know that Each home has its own well which is used to draw water from well. More than that, each home has its own electromechanical system for getting the water from the well to the house. At the heart of each system is a pump. So we need to decide where to purchase these pumps which can provide us warrenty and services.
Shallow Well Pump

mandrews44 said...

Permeate pumps are designed to reduce the back pressure on the membrane and removes TDS creep as you use the system and constantly create back pressure, thus lowering it's efficiency and forward pressure. Without one, your TDS will continue to increase as you top off the system over a 6 month period. I've tested this in a lab environment and when the membrane is producing at a high back pressure from the storage tanks, TDS tends to go way up. The flow restrictor will keep the waste water at a constant but rejection rates go way up and little RO water is produced. I've seen 120ppm during my tests. I've had this new 50 GPD system for about a week now and I measured the TDS when the tanks were fulling and it was 10 ppm. TDS is at 18 now a week later. Currently, my incoming supply TDS at 260 ppm which is a little higher than the original test I did and I tested 12 ppm with a little pressure on the Membrane. Permeate pumps are designed to keep the back pressure to a maximum of 5 psi which means you won't get a higher TDS and lower recovery rates as your tanks fill up. Drawing only enough water to activate the pressure switch is the worse thing you can do with these systems unless you have a Permeate pump. It is true that supply pressure has something to do with it because 40 psi coming in and your tanks are at 45 psi, you have -5 lbs pressure on your OS membrane. You will product no water at those pressures. Either you have to increase your input pressure higher then your tank pressure or use a permeate pump to fix that for you.

costas mavros said...

hello i am trying to learn about the desalination process. I do not know much but I understood from this post that as long as the tank is empty and the pressure of the seawater that is inserted to the system is higher than the pressure of the clean water tank, higher amount and more efficiently the water is cleaned. So what if there was a sensor that will understands when the pressure of the tank is getting higher and will transfer the clean water somewhere else, so the tank will be empty again. will that help the desalination process to be more efficient and use a lot of amount of the water that was inserted in the product? Thank u in advance

The Player said...

costas, this kind of system is for home use. The cheapest was sold for US$99 and up to a few hundred dollars. For larger scale systems, you will have to keep the pressure across the membrane high enough at all times. This can be done by several means. In residential systems, the tank is the cheap way to get the water out to drink, so therefore it is pressurized when the water is filtered. Larger scale systems will not need to pressurize the water. You just need a pump to deliver the water.

Shannon Gomes said...

I'm new to the whole RO world. Can you explain why water quality changes with pressure across the membrane? My understanding is the membrane only lets through very small particles. How would pressure change the size of particles moving through the membrane?

The Player said...

Sorry, I only visit the blog when I have new content.

The pressure across the membrane is the driving force - passing water through and very little impurity. The performance depends on the pressure. It's like many things - like the voltage across battery. Other than that it's pure physics that words can't describe more.