Building waterchange station

Richmond · Jul 18, 2018

I know there are countless threads, but I have a few questions and I'm struggling to find a concrete answer.

1) If I'm hoping to run a ~50 foot hose from my NSW to my tank, what sort of pump should I consider?

2) Should I put a check valve between RODI water and the NSW? Seems like it would make sense to keep salt out of the RODI?

3) A T-fitting on the intake and output of the pump, along with shut off valves should allow one pump to pull water from RODI to NSW and then from NSW to tank, am I over thinking this being difficult?

I think I have some others, but thanks in advance.

Greybeard · Jul 18, 2018

50' from mixing station to tank... Pump size is going to be dictated by desired flow rate and head pressure. How big of a water change to you do, and how long are you willing to wait for it to refill after a change?

In my case, I have a very short distance from mixing station to tank... just a couple of feet. I'm using a (very old) Mag 1100 pump to pump back to the tank, through a length of 5/8" silicone tube. Head pressure is increased by using flex hose through a fairly circuitous route (passing through a wall), pumping 'uphill' about 4 feet, and the 1/2" manual valve at the end of the hose.. Takes me about 5 minutes to refill after a 30 gallon water change. That means I'm getting about 360 gph out of a pump rated for 1100 gph.

If you're pumping through 50' of plumbing, your head pressure could well be very high. I'd plan on some sort of pressure rated pump, at a rate of flow as needed to suite your needs. Perhaps an RT series Iwaki?

Check valve... not sure how you'd get flow _backwards_ into a pressurized system. I don't believe it would be necessary, but a 1/4" RO check valve is cheap... no big deal to go ahead and put one in.

One pump, split intake and outlet, manual valves... could work. One thing to consider, you're going to have some mixing... cross contamination. The valve and plumbing is going to be full on salt or fresh after you change inputs. For instance, you're likely to get a bit of fresh flowing before the salt flushes it out when returning to the tank. If the tank is big enough, or the plumbing small enough, it won't matter much, but it's something to be aware of.

Richmond · Jul 18, 2018

Thanks for the thorough response. I was thinking of putting the check valve between the RODI reservoir and the salt mixing tank, not from the RODI unit to the reservoir.

I think I'll do a small pump to move water from fresh water reservoir to NSW mixing tank, and then a separate pump to move it into the house, so it doesn't contaminate. That will also allow me to plumb the output pump back into the tank to mix the salt. Easy peasy, thanks again for the response.

Richmond · Jul 18, 2018

As a follow up, I found a pump with these stats:

max flow: 3962 gph, max-head: 16.4 foot

Does the max-head mean it can carry water UP 16.4 feet or the length of 16 feet? Would this pump suit my needs based on the above stat?

Greybeard · Jul 19, 2018

Richmond said:
As a follow up, I found a pump with these stats:

max flow: 3962 gph, max-head: 16.4 foot

Does the max-head mean it can carry water UP 16.4 feet or the length of 16 feet? Would this pump suit my needs based on the above stat?

It means that the pump has the capability of pushing water straight up at a height of 16.4 feet. I don't know how you're running your lines... 50 feet is quite a ways, but if it's not all straight up, this pump is likely fine.

The term 'head pressure' is expressed in terms of moving water straight up... but moving water up is not the only thing that adds head pressure. Every bend of the pipe adds some head pressure. Even running through a really long straight pipe adds some head pressure, due to simple friction. It would be impossible for me to say how much head pressure you're going to have over that 50' run of pipe. Depends on how many corners you have to run through, how wide the pipe is, if you're using sharp corners or sweep corners, any vertical movement in the run... just too many factors to consider.

But... all that said, 16' is a pretty high head pressure rating, and 4k GPH is a LOT of flow. I'd guess you'll be fine with that pump. I'd try to stay with the same size pipe all the way through as the pump's outlet size.

Richmond · Jul 19, 2018

Thanks again for the responses! I think I've got a decent plan in my mind. Working on cleaning out the barrels I picked up yesterday and I'll start construction.

dbl · Jul 19, 2018

@Greybeard pretty much has you covered, but I thought I'd offer an article that discusses the topic in case you haven't run across it yet. May give you an idea of two and then again it may not.

You will love a well designed changing station.

https://www.reef2reef.com/ams/let’s-mix-it-up-designing-and-using-a-water-mixing-station.77/