10” vs 20” prefilter

[Vtmbz]

New to me used ro has 3 4x40 membranes, and 20” filter. Previous user said it ran best at 90-120 psi. Do ireally need 20” filter? Im running around 500 taps and used to,changing my prefilter daily in use, or about 300 gallons of sap.

[carls47807]

That pressure seems low, I would want 175psi minimum at the membrane inlet. You can run a 10" filter, but you need something at 5 micron before the membranes.

[maple flats]

Give us more information please. That pressure is very low. What make is the RO if factory made. If homemade, what pump does it have? Are the pressure canisters for the membranes stainless steel or PVC? Are there flow meters? If yes, what flows are printed on each for max?
I'm not familiar with any RO with 4x40 membranes that runs at under 175 or 200 PSI. Mine runs at 275-300 PSI.

In terms of the prefilter I'd think you will want 20", that is standard for most if not all with 2 of those membranes, with 3 i don't think you would have enough filtering surface to do the job, it would plug up too soon.

Try these https://www.supplyhouse.com/iSpring-FP25X25-High-Capacity-20-x-2-5-Fine-Sediment-Water-Filter-Replacement-Cartridges-25-Pieces?utm_source=bingad&utm_medium=shopping&msclkid=d0cb08f5e4e2117e79b76d84f642fef7
Shop around for better prices. If you buy 2 cases, the shipping is free, I always bought enough to get free shipping. I suggest you only use polipro filters, not string wound. The string wound are often a problem to get into the filter housing without any leaks or poor filtration. If you buy small quantities you will pay 3-6x as much, maybe more. Keep critters and moisture out of the cases and the filters will last several years.

[Vtmbz]

This is an older home built r.o. It has a lp pump and a rotary vane hp pump. The relief pressure on that is 240 psi, four gals/mimute output.
It has full instrumentation; sap temp and sap pressure, comcentrate pressure. Three 4x40 ss pressure vessels. Theres a wash cycle and tank. The membranes are run in parallel, not series.

The output perm and conc lines are 1/2”, and the sap line starts put 3/4” but hits 1/2” before the twenty inch filter. There is also some domestic 1/2” pvc out of thr flow meters.
Heres the odd part: the lp pump is meant to be used in the wash cycle, but not in rinse or run cycles, according to thevalve settings. Im not sure yet but the valving indicates that the lp pump is not a booster

So the conclusion there is that the vane pump was enough to run the thing. I imagine that i can get lots more pressure out of the thing with maybe new donuts and orings on the pressure vessels.

Anyway, based on the pressures involved, i wonder if i can switch to a 10” 5micron filter, and use up the case of 10” filters i have.
This is intended for less than 500 taps. I change my filter every 300 gallons of sap.

[maple flats]

In that case, I'd try running at 200, then 210 and max 220psi, see how it performs. It's indeed possible the 175 will work best but I'd experiment to verify. Send me in a P.M. your email, I'll send you generic instructions that will likely help in all of the proceedures that will help you get the best performance from your RO.

[Vtmbz]

That pressure seems low, I would want 175psi minimum at the membrane inlet. You can run a 10" filter, but you need something at 5 micron before the membranes.

I left out one tiny detail: the membranes are not installed. No dpubt they raise the pressures a bit?