New RO Membrane Troubleshooting

[ajdelange]

Putting a pump in the feed line after the pre-filters sends the feed to the membranes at high pressure thus increasing the recovery (permeate flow relative to concentrate). Systems sometimes have additional pumps. For example the permeate in my system is accumulated in an atmospheric tank and a second pump is used to transfer water from the atmospheric tank to a pressure tank. The pressure tank is plumbed to the brewery and lab.

 

[mabrungard]

Membranes used in small home-based RO machines have a much lower feedwater pressure capability than the industrial units I design around. In addition, these home-based membrane manufacturers only recommend booster pumps when the feedwater pressure is below their specifications. Be sure to consult the membrane manufacturer's pressure recommendation and your water supply pressure before throwing a booster pump on your system. The membranes can be ruptured by excessive pressure drop across the membrane.

If you are using a cascading set of membranes in series, then it is possible to use a booster pump on the first stage when the subsequent stages impose adequate backpressure to avoid excessive pressure drop across the membranes.

 

[The_Bishop]

Martin, the Filmtec membranes can deal with 150PSI. I had the same concerns as you so I browsed the Dow website for info.

It's been my experience that the more pressure you feed the membrane (Within reason, and under the maximum) the more permeate is generated and the higher the rejection rate.

When I say I have two membranes in series, I don't mean I have permeate running from one membrane into a second; I have the feed water running into the first membrane, and the concentrate from the first membrane runs into the feed water fitting on the second membrane, then to the flow restrictor and out. The permeate lines are tee'd together and run to the collection point. In essence, I'm turning two 75GPD membranes into a longer 150GPD. With the added pressure I'm actually generating in the neighborhood of 200 GPD at 4-5 TDS.

 

[Buckeye_Hydro]

From our booster pump instructions. Your system may not have the DI stage, or all the other pump accessories shown.

Russ

 

[daveMN]

From our booster pump instructions. Your system may not have the DI stage, or all the other pump accessories shown.

Russ

This really helps. Thanks, Russ. The pressure switch is the piece I was wondering about.

 

[Buckeye_Hydro]

For a closer look, http://www.buckeyehydro.com/high-pressure-switch/

 

[Buckeye_Hydro]

The weakest link in residential systems in terms of ability to withstand elevated pressures is typically the clear housings. This is the reason we recommend putting the pump AFTER all the prefilters.