Adding a third membrane to RO system

[APW]

Has anyone ever added a third membrane to a two membrane system. It has a 1 hp pump now. Thinking I would need to go up to a 1.5 hp but no sure if I would need to increase all the hose sizes or leave them the same? Or would I better to just spend the money and buy a new 3 membrane system. I can get a brand new one from Waterguy RO for $3925

 

[MEP001]

It would certainly be easier to replace the system, but most new ones are designed so poorly that IMO you'd be better off adding a membrane.

I'd recommend going up to a 2 HP pump and setting it up for some of the reject to return to the pump. This increases the output and reduces the reject waste at the same time.

 

[APW]

Would I have to increase the hose sizes?

 

[mac]

It will be much easier and cheaper if you just increase the holding tank size

 

[MEP001]

Would I have to increase the hose sizes?

If you split the output of the pump to the three membranes, you won't. I don't know if you can run all that water through three membranes, and I doubt that would be a good idea. You might have to combine the reject from the three membranes into a 3/4" or 1" pipe back to the pump and come off that for the waste. If you want meters, you'll need bigger ones - I check it with a cup or a pitcher and a stopwatch whenever there aren't working flow meters.

 

[AnalyticWash]

It will be much easier and cheaper if you just increase the holding tank size

this. unless you don't have the space.

 

[APW]

If you split the output of the pump to the three membranes, you won't. I don't know if you can run all that water through three membranes, and I doubt that would be a good idea. You might have to combine the reject from the three membranes into a 3/4" or 1" pipe back to the pump and come off that for the waste. If you want meters, you'll need bigger ones - I check it with a cup or a pitcher and a stopwatch whenever there aren't working flow meters.

MEP would you run 1/2" lines from the pump outlet and feed all three membranes at the same time or should I go in and out of each membrane and feed the next one? Also what size meters would you recommend?

 

[MEP001]

I would come straight from the pump outlet to three separate 1/2" hoses for the three membranes. The reject from the three membranes could return to a single manifold with two adjustments, one to the drain and one going back to the pump. You'll need meters that read at least 6 GPM. I would recommend a 2 HP pump for three membranes - a 1-1/2 HP is barely big enough for two. Circulating part of the reject back to the pump gives you more flow through the membranes and increases the efficiency.

 

[APW]

I actually bought a 2 HP pump. Thank you for your help.

 

[soonermajic]

Is just getting a Larger holding tank not an option?
Also, I wonder if the reject water is plenty good enough for SS bays hp rinse water? Mine is all hard plumbed for hot water, & we spend a $hit ton on ,Salt, RO, gas ,& just plain water.

 

[MEP001]

Is just getting a Larger holding tank not an option?

It is if you have the room, but since it's been mentioned several times and OP hasn't gone with that, I assume it's not a solution for him.

Also, I wonder if the reject water is plenty good enough for SS bays hp rinse water?

Yes, but it's a lot of trouble to reliably introduce it into the system. It's easier to have some of it trickle in with the hot water from an elevated tank. It's still soft water, it's just a higher TDS.