Time For A New Membrane. Suggestions?

[cham]

I think its time to replace my membrane. Its almost 2 years old and has always produced 1 or 2 TDS right after the membrane but before the DI. Now is up around 6 or 7 so I suspect its in need of replacement.

When I bought my RO/DI two years ago I wans't sure what to get so I bought the 4 stage 100gpd unit but I thought that I later read that the 75 gpd was a better membrane.

Any suggestions on what membrane to get? I was looking at the DOW 75 gpd.

My tap TDS is pretty low at 130 or so.

[ReefDent]

If your tap has a TDS of near 100 ppm, then 6 or 7 ppm TDS is still 93-94% rejection. For a 100 gpd membrane, that's actually pretty good. I'd try flusing the membrane (remove the flow restrictor for a few seconds or use a flush kit) and see how that does. I think you've got at least a few more months there.

James

[cham]

<a href=showthread.php?s=&postid=11062880#post11062880 target=_blank>Originally posted</a> by ReefDent
If your tap has a TDS of near 100 ppm, then 6 or 7 ppm TDS is still 93-94% rejection. For a 100 gpd membrane, that's actually pretty good. I'd try flusing the membrane (remove the flow restrictor for a few seconds or use a flush kit) and see how that does. I think you've got at least a few more months there.

James

The flow restrictor is the rubber piece in the waste exit tube?

[DarG]

I would replace the membrane. It may have some life left but at 2 years old it's getting there and the 6 or 7 PPM TDS after RO eats the DI resin a whole heck of alot faster than 1 or 2 PPM. Of course, if you can flush it and get back to 2 PPM then great but personally, at 2 years, I'd just go with a new 75 GPD membrane and be done with it.
75 GPD is a wise choice because it offers the higher, 98% (spec) rejection. You do need to change the flow restrictor which may be a plug in the waste port of the membrane housing. When you order the new membrane, add an external inline flow restrictor to the order. They are only 5 or 6 bucks and they are better than the plugs from what I hear. You can get them with the John Guest fittings so all you have to do is cut the waste line and put the restrictor right in line. You should remove the old plug type flow restrictor. I think that the Dow Filmtec membranes are still supposed to be the best so I would go with the Dow Filtec. Cant go wrong there.

[cham]

Hmmm

This is the first I've heard of replacing the Capillary flow restrictor when you replace the membrane.

Any others do this too? Should I change it when going from a 100 gpd to a 75?

[DarG]

They are calibrated for the membrane rating to achieve an approximate 4:1 waste to product water. For a 75 GPD membrane you should use a 75 GPD flow restrictor.

http://www.thefilterguys.biz/ro_membranes.htm

[reef_doug]

Most 100 gpd flow restrictors are unique. The 60 & 75 gpd most always share the same flow restrictor, so yes you'll need a new one, only a few bucks though.

Many people favor the 75 gpd units because the popular Dow Filmtec cartridge for 60 & 75 is about 98% rejection. The Dow Filmtec for 100 GPD is about 90%. Thus your DI may last longer on a 60-75 GPD unit with higher rejection than a 100 GPD.

With proper DI, the end product should be 0-2 TDS.

I'm learing that some silicates can and do slip through membranes and TDS monitors may not pick them up because of a weak ion or something. Thus if you have 0 TDS, you may still have Silicate without knowing it and it's difficult to test for. There are different DI's for different purposes. Check out Spectrapure.com on DI filters. Also check with you water district for silicate content.

[cham]

I took my old membrane out.

Turns out I have a 50 gpd membrane & my flow restrictor is blue. So it sounds like a need to buy a 75 gpd restrictor and a new membrane.


Edit: It says the blue is good for 55 gpd at 4:1 ratio and 75 gpd on the 3:1. I have no idea what ratio mine is. How do I find that out?

[ReefDent]

That changes things signigicantly in my mind. The
Dow filmtec 50 and 75 gpd membranes should be giving a 97-99% rejection, so I think you made the right decision. Get a new one, and if you change the size, get a new flow restrictor.

James

[DarG]

<a href=showthread.php?s=&postid=11067689#post11067689 target=_blank>Originally posted</a> by cham
I took my old membrane out.

Turns out I have a 50 gpd membrane & my flow restrictor is blue. So it sounds like a need to buy a 75 gpd restrictor and a new membrane.


Edit: It says the blue is good for 55 gpd at 4:1 ratio and 75 gpd on the 3:1. I have no idea what ratio mine is. How do I find that out?

You can measure the product water and waste water over a given time period and calculate the ratio. But it's really not something you need to do. Just get the right flow restrictor for the membrane you get and check your TDS. If it's very low after RO (About 98% for a filmtec 75 GPD) and 0 after DI, everything is working great. I have a Dow filmtec 75 GPD. My supply is about 160 PPM TDS and I get 1 or 2 PPM after RO, 0 after DI. If your water pressure is within the membranes operating range, everything usually works fine with everthing installed properly.

[fours2many]

I do not have a flow restrictor on my unit. Do all RO/DI units need one? Is it only needed if there is no way to slow the water pressure down? I have a valve on my water entering the unit and keep the pressure at 65.

I am now copnfussed.

[DarG]

You need a flow restrictor on the waste line. It creates backpressure on the membrane forcing water to pass through it. If you didnt have a flow restrictor, you probably wouldnt be producing any RO water or very little. A lot of teh time, the flow restricor is actually in the waste water port of the Membrane housing. It's like a little plug in the port itself where the waste line connects. It also can be a little plug in the end of the waste tubing itself. So, just because you dont see one doesnt mean you dont have one. If your unit is producing RO water, there is a flow restrictor somehwere.

[Buckeye Hydro]

<a href=showthread.php?s=&postid=11068026#post11068026 target=_blank>Originally posted</a> by fours2many
I do not have a flow restrictor on my unit. Do all RO/DI units need one? Is it only needed if there is no way to slow the water pressure down? I have a valve on my water entering the unit and keep the pressure at 65.

I am now copnfussed.

You actually do have a flow restrictor - or your system would not produce any purified water.

The restrictor may be INSIDE the elbow fitting in the waste port of your RO membrane, orr INSIDE the waste water tube.

If you can control the water pressure reaching your system, and have more than 65 - crank that up to about 85 psi.

Russ

[cthetoy]

Don't forget the newer DOW Filmtec 150gpd membrane has a 97% rejection rate unlike the 90% for the 100gpd

[Buckeye Hydro]

Actually our new 150 gpd membrane is a Buckeye Brand, rather than a Filmtec. Filmtec doesn't make a 150. It is a high rejection membrane as you mentioned.

Russ

[old salty]

I have the 150gpd membrane from BFS. With the pressure pump installed, and a ball valve on the output (for proper flow restriction), at 80psi, I am making 180pgd with a 98% rejection rate. I am happy to make water so quickly and the high rejection rate really saves on DI resin.

[ReefDent]

I had seen this one not too long ago and wondered if it would really have a nice high rejection. It sounds like it does.

Can two of them be used in a dual 75 gpd system to do 300 gpd instead of 150 gpd?

James

[Buckeye Hydro]

We've not tried that configuration. In theory it would work just fine. I suspect you'd want to go with 3/8" tubing on the supply and waste lines.

[Buckeye Hydro]

Let me rephase that. Yes - you can plumb in parallel or in series two membranes. If in parallel, use two flow restrictors. If in series use a single flow restrictor designed to handle 4 x 300 gpd flow of waste water (you'll not find a standard flow restrictor available to handle this amount of flow).

The supply line and waste line (if combined from both membranes) will likely need to be 3/8" tubing.