Low RO output

[RAATCB]

I just replaced my 2 membranes due to a permeate flow drop. After replacing membranes the flow rate increase to the maximum gpm (2.5) which I need to keep up with production. Today(1 month later) I checked permeate flow rate and it decreased about .5 gpm.

System makes 2.5 gpm permeate max or "3600 gpd"
Maximum pressure threw membranes = 200 psi
Current pressure = 150psi (pressure can be reduced but cannot reach 200psi)

I tried adjusting the regulator to increase pressure but the regulator cannot go any higher than 150psi.

My question, is my regulator the problem or is it my pump(procon). The owners manual says if a 200psi pressure cannot be reached and flow rate is not maxed out "2.5gpm" the pump might be losing efficiency.


Any advice ?

 

[MEP001]

What is your permeate to concentrate ratio?

Does the system recirculate a portion of the reject? (Sounds very unlikely with a 3600 gpd system running a Procon).

Is your water soft?

 

[RAATCB]

Ratio should be at least 50% recovery or more. I do not have a reject flow meter, but I've looked and seen little reject water coming out of the drain line but for a fact I visually see a lot more permeate flow if I look at the top of the tank where the product water flows threw.

System does recirculate, right before reject solenoid the line is tee'd back to membrane.

Water hardness = 0 grains.
Carbon media = New 1 cu. foot

What sounds wrong ?

 

[RAATCB]

Also, my procon pump is rated for 240gph/4gpm, if it currently makes 2 gpm permeate and lets say rejects "2gpm" total gpm is 4 gpm which is maxing out the pumps gpm. Can that be a reason why my permeate cannot increase to another 0.5 gpm?

 

[mac]

How old is the Procon? I never thought these were good pumps. Open one up and you'll see why. They use "floating" carbon vanes that slide in and out as it turns. After a while the vanes just wear out.

 

[RAATCB]

Not sure exactly how old the pump is, I bought car wash a few years ago. I would say at least 7-8 years old.

 

[MEP001]

The system pressure can be up to 200 PSI, but it doesn't have to be. You should not be rejecting LESS than you're making. Either the pump is going out or it's undersized. Is the Procon the one with 1/2" ports?

There's nothing wrong with Procon pumps. They can last 20 years if they're never run dry.

 

[RAATCB]

I cannot regulate the pressure higher than 150psi. I am rejecting less than what I'm making. My Procon#104E240F11XX with 1/2 ports. Before I changed membranes I tried increasing pressure threw old membranes to make more product, I did see pressure reach to around 180 psi. After new membranes installed in the beginning I was making 2.5 gpm @ 100psi. I slowly noticed after a month the product flow rate droped and I was able to increase pressure to 125psi to again achieve 2.5gpm. Now product dropped a little more and now i increased psi to 150 which the regulator cannot go any higher(it's at the maximum) and the greatest product flow rate achieved is 2.0 gpm.

MEP001, what's your advice?

 

[MEP001]

That Procon is too small. You need this pump or something with the same ratings:

https://www.kleen-ritecorp.com/p-33288-dayton-5nxz9-booster-pump.aspx

The reason your product decreased and you were able to increase pressure is because the membranes were getting fouled.

 

[RAATCB]

MEP001, I've achieved 2.5 gpm flow rate out of this pump before. The flow rate dropped to 1.5gpm a few months ago because of membranes becoming foul. Now that i have new membranes, the first month I achieved 2.5 gpm than slowly start dropping.

When the membranes were first installed the membranes were producing 2.5gpm @ only 100psi.
Now i noticed @ 100 psi the flow rate was only about 1.5gpm, yesterday i increased pressure to 150psi (max) and flow rate only increased 0.5gpm.

MEP001, is there any way i can call you? It's a little difficult explaining threw typing.

 

[MEP001]

I understand perfectly what's going on.

1. The pump is too small for two membranes.

2. There is not enough reject flow to keep the membranes from getting fouled.

The solution is the proper size pump for two membranes. The way it is now, in order to make 2.5 GPM of product, you're forcing almost all the water through as permeate and not enough flowing through to keep them from getting fouled. There should be one part permeate, one part reject and about two parts recirculating through, otherwise you need to have one part permeate and a minimum of two parts reject.

 

[RAATCB]

So my choices are:

1. Keeping my product water GPM slightly lower so it can have enough reject flow?
2. Changing the procon pump to a higher GPH? Currently pump capacity is 240GPH or 4.0 GPM

I'm not sure if i'm understanding what "one part permeate,one part reject and two parts recirculating" means

 

[MEP001]

If you have 1:1 permeate to reject, some of the reject needs to bee tee'd back to the pump inlet to increase flow through the system. There's no way yours can do that with a single Procon pump - it can't flow enough. You also just confirmed that there's nowhere near enough volume from the Procon since you were producing 2.5 GPM, since you'd be rejecting less than that.

A third option would be to remove one membrane.

 

[johnny]

what about the water temperture

 

[MEP001]

Temperature makes a very, very small difference.

 

[RAATCB]

What would be the minimum size procon pump (GPH) I would need? My motor is 1hp.

 

[MEP001]

There is not a Procon big enough. You need a minimum of 7.5 GPH at 200 PSI.

 

[RAATCB]

MEP001, right now I'm making 2.0gpm permeate. When I look at the drain/reject flow line it seems to draining very little reject compared to what it's making (2.0gpm) If I was recovering 50% that means the same about of product flow would be draining out, but it's nothing near that amount. Do you know if that's normal? It seems that I'm recovering a lot more than 50% since so little is draining out. What's your thoughts?

 

[MEP001]

It's not normal. You should be rejecting a bare minimum of 1:1, and as I said before it would need to be "recovering" twice as much as it's making to be at 1:1. There's no way to achieve that with a Procon pump and two 4x40" membranes.

 

[Jeff_L]

I know you two are in a discussion, but let me throw my own observation in so you can base some of your thoughts around your setup.

I use a booster pump, not a pro on. Cannot remember the flow rate on it, but it's the standard one Windtrax sells. I've always kept my pressure at 200psi until I changed my membrane under normal maint a couple months ago. I decided to read the directions, and it recommended a psi of no more than 150 and use of cold water. This will slow the fouling by not push water as hard against the pours, and the warm water would make the pours expand. Neither of which sounds good.

I'm rejecting more than 1:1, probably more like around 1:3, and it's always been that way for me. I just put in two new PDQ autos this year and use a tone more SF than I was before. I think I have enough pump to put in a second membrane to try and keep up this winter.