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RO membrane filter
- Thread starter Ontheeyes
- Start date
Wow that is a big pump. What kind of motor are you using for the pump? How are the no name membranes working out for you still?
MEP001
Well-known member
It will increase the flow through the membranes which will let you reduce the reject rate to 1:1, and it may slightly increase the production rate.
Did you ever go with this pump setup? If so. how is it doing for you?
Buckeye Hydro
Well-known member
Guys - If you do some homework re the RO membranes, pay attention to the pressure spec of the particular membrane you're looking at. For instance:
"Low Energy" membranes are available - and practically speaking you can think of them as "Low Pressure" membranes.
Assuming you have the appropriate pretreatment, understand the minimum concentrate flow, and the expected permeate (RO Water flow) given your pressure and water temperature. Check all that against your concentrate and permeate flow gauges and pump pressure gauge.
Russ
Assuming you have the appropriate pretreatment, understand the minimum concentrate flow, and the expected permeate (RO Water flow) given your pressure and water temperature. Check all that against your concentrate and permeate flow gauges and pump pressure gauge.
Russ
GeorgeFrankie
Banned
You don’t have to buy from Hydro Spray—just make sure any 4"x40" membrane you choose matches the specs. You can likely find a cheaper option elsewhere.
Buckeye Hydro
Well-known member
The two primary specs you want to match up are diameter and length which you've already done (4" x 40" nominal) and the pressure at which you run the system. For instance, we stock membranes with pressure specs @ 80 psi, 100 psi, 150 psi, and 225 psi.
https://www.buckeyehydro.com/4-diamter-ro-membranes/
We are in the process of stocking some lower cost membranes, which seem to be what many in this industry are hunting for.
You want to buy a membrane that is spec'ed at your typical running pressure or below. In other words, you'd not want to run a 225 psi membrane at 100 psi; but it is fine to run a 100 psi membrane at 225psi. If you exceed the pressure spec on a membrane you'll get better than spec performance. Max operating pressure for these types of membranes are typically very high (e.g., 600 psi) - well above what most fresh water commercial RO's can produce.
Russ
https://www.buckeyehydro.com/4-diamter-ro-membranes/
We are in the process of stocking some lower cost membranes, which seem to be what many in this industry are hunting for.
You want to buy a membrane that is spec'ed at your typical running pressure or below. In other words, you'd not want to run a 225 psi membrane at 100 psi; but it is fine to run a 100 psi membrane at 225psi. If you exceed the pressure spec on a membrane you'll get better than spec performance. Max operating pressure for these types of membranes are typically very high (e.g., 600 psi) - well above what most fresh water commercial RO's can produce.
Russ
Wash Dragon
New member
From what we understand, they are using high-pressure membranes at relatively low pressure, like city water pressure, to increase production.
They said that if they use low-pressure membranes, the production rate would be too low and it would quickly run out of water.
They said that if they use low-pressure membranes, the production rate would be too low and it would quickly run out of water.
Wash Dragon
New member
Wouldn't operating above the rated pressure damage the membrane?
From what I know, it's actually the opposite — running a low-pressure membrane at high pressure tends to shorten its lifespan.
I’ve heard that using a high-pressure-rated membrane at lower pressure results in lower efficiency, but still provides more permeate than a low-pressure membrane under the same conditions.
Buckeye Hydro
Well-known member
The devil is in the details here. What is your pump output pressure? What membranes are installed?
When a manufacturer provides a temperature and pressure spec on a given membrane, nothing says those conditions are "ideal." They are just the conditions provided to the membrane during testing, and those conditions resulted in x gals per day production of permeate (RO water). Let's say the spec pressure is 150 psi: if you run it at 180 psi, the membrane performance will be better - both in terms of amount of permeate produced, and purity of the permeate. If you check into the fine print, max recommended pressure might be something like 600 psi.
Hate to say it, but most often when vendors sell someone something like a 225 psi 4040 membrane designed to produce ~2600 gpd, and tell you it's ok to run it at your pump's max of let's say 110 psi, (we even see some vendors suggesting unsuspecting customers run these membranes at line pressure [typically 50 to 60 psi]) the primary beneficiary of that sale is the vendor. They sold you a membrane much more expensive than need be, and it is not well matched to your system.
When a manufacturer provides a temperature and pressure spec on a given membrane, nothing says those conditions are "ideal." They are just the conditions provided to the membrane during testing, and those conditions resulted in x gals per day production of permeate (RO water). Let's say the spec pressure is 150 psi: if you run it at 180 psi, the membrane performance will be better - both in terms of amount of permeate produced, and purity of the permeate. If you check into the fine print, max recommended pressure might be something like 600 psi.
Hate to say it, but most often when vendors sell someone something like a 225 psi 4040 membrane designed to produce ~2600 gpd, and tell you it's ok to run it at your pump's max of let's say 110 psi, (we even see some vendors suggesting unsuspecting customers run these membranes at line pressure [typically 50 to 60 psi]) the primary beneficiary of that sale is the vendor. They sold you a membrane much more expensive than need be, and it is not well matched to your system.
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Wash Dragon
New member
If the pressure rating is not provided by the manufacturer (or is unclear), I believe it's safe to operate below the tested pressure.
In that case, using a high-pressure-rated membrane under the same conditions provides an extra safety margin against membrane failure.
Especially with membranes from Chinese manufacturers, I consider it risky to go above the tested pressure.
For reference, our operating environment is around 100 PSI, with a maximum of 190 PSI.
Buckeye Hydro
Well-known member
If a membrane manufacturer does not provide the pressure spec... do not buy the membrane.
Can't say, that after 25 yrs of doing this, I've ever seen a max pressure that wasn't well above the test pressure/pressure spec. I wouldn't consider buying a membrane if the test pressure approximated the max pressure.
Would be like putting oil in your truck w/o knowing the viscosity - or installing a pump with unknown voltage requirement/capacity - or buying paint w/o knowing the color. The pressure spec of a membrane is THAT fundamental.
Can't say, that after 25 yrs of doing this, I've ever seen a max pressure that wasn't well above the test pressure/pressure spec. I wouldn't consider buying a membrane if the test pressure approximated the max pressure.
Would be like putting oil in your truck w/o knowing the viscosity - or installing a pump with unknown voltage requirement/capacity - or buying paint w/o knowing the color. The pressure spec of a membrane is THAT fundamental.
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toddmullens
Active member
The membrane housings are usually the weak point as far as pressure goes. I have exploded pvc housings and stainless housings, although I think the stainless housing had a defect where the end caps attach. Maybe I’m just lucky! Never ran anything above 220 psi knowingly.
Wash Dragon
New member
I completely understand your point — and I agree, ideally, a membrane should come with clearly defined pressure specs.
However, in practice, especially when dealing with some overseas suppliers, we sometimes find ourselves in situations where the only available data is the test pressure.
In such cases, we take a conservative approach and operate well below that test pressure, usually around 100 PSI in our system (with a max of 190 PSI). This allows us to build in a safety margin, especially when using membranes rated for higher pressure.
That said, I do share your concern — if the test pressure is close to the max operating pressure, it definitely raises a red flag. I wouldn’t trust a membrane under those conditions either.
Also, from our experience, low-pressure membranes often can’t provide enough flow and we run out of water quickly.
Our setup is limited by space — we had to bring in multiple small tanks through a narrow doorway, so our total storage capacity is only about 250 gallons.
That’s another reason we rely on high-pressure membranes even if we operate them at lower pressures.
Buckeye Hydro
Well-known member
Based on a career worth of experience with RO membranes, I think your concern re over pressurizing membranes is misplaced. Maximum pressure always far exceeds test pressure. If you run below test pressure, you will reduce the gals per day of purified water produced, and you will (potentially significantly) reduce the purity of the RO water. If that's not an issue for you... so be it.
Membranes spec'ed at lower pressure will produce MORE RO water at any pressure relative to a membrane spec'ed at higher pressure... assuming they both have the same GPD spec.
I'm not understanding why the size of your multiple smaller storage tanks has anything to do with running a membrane at pressures far below spec.
