Prefilter micron; before or after pressure pump

[maple marc]

Does everyone use 5 micron pre-filters? 5 is too tight for my RO system that relies on gravity feed (no supply pump). Pressure pump gets starved. Manufacturer suggests using 10 or 20 micron, and possibly adding a small supply pump.

My pre-filter is before the pressure pump--hence the problem it creates by starving the pump. I have seen pre-filters installed after the pressure pump. Is this the most common setup? How much pressure can the pre-filters handle?

[maple flats]

I've only seen ones with a feed pump. They have the pre-filter after the feed pump and before the pressure pump.

[maple marc]

Thanks, Dave. Sorry to see the news about your bad hip.

[canaanmaple]

I think I am having the same issue with pressure pump being starved. I want to add a low pressure pump, since I want to expand the RO and add another membrane anyway. Does anyone know if this will work well as a low pressure pump?

https://www.chuggerpumps.com/product/xcpss-in-1-115v/

thanks!!

[wnybassman]

My RO is a pressure pump only model, with the filter before the pump. I found early on it will only work well with one particular brand of filters, Purtrex. They are the "fuzzier" ones, and not the smoother ones, if that makes any sense. The smoother ones very much starved the pump.

[maple marc]

I feel like I'm trying to reinvent the wheel here with my problem as mentioned by others here: Procon pressure pump (approx 4 gpm max with pressure valve wide open) is being starved by gravity feed through pre-filter. Ray at Deer Run says try 10 micron cartridge instead of 5 micron--or maybe use feed pump. Maybe the Purtrex filter cartridges will work. If I go with a feed pump it seems impossible to find one that feeds just over 4 gpm that doesn't rely of oil lube. What do you RO veterans advise for us RO rookies?

[wnybassman]

I feel like I'm trying to reinvent the wheel here with my problem as mentioned by others here: Procon pressure pump (approx 4 gpm max with pressure valve wide open) is being starved by gravity feed through pre-filter. Ray at Deer Run says try 10 micron cartridge instead of 5 micron--or maybe use feed pump. Maybe the Purtrex filter cartridges will work. If I go with a feed pump it seems impossible to find one that feeds just over 4 gpm that doesn't rely of oil lube. What do you RO veterans advise for us RO rookies?

I would definitely give the Purtrex PX05 filter a try first. Anything else and I could visibly see air bubbles in the tubing between the filter and the pump.

[DrTimPerkins]

1. Try 10 micron filters.
2. Is the line after the filter clear....if so, can you see ANY bubbles? If so, that's the problem. Air leaks on the suction side can cause the pump to shut off.
3. Is the tank level above the level of the RO? Any amount of head pressure you can get will be helpful.
4. Put a small bleeder valve in the line at a high point, but close to the RO to make sure you're getting every bit of air out. How long is it running before it shuts off?
5. If all else fails, try (for a short test) removing the filter cartridge and running it for a little while. That'll help diagnose whether it is air or the restrictions due to the filter or something else causing the problem.

[maple marc]

Thank you for ideas.

1. I have ordered Purtrex "fuzzy" 5 micron cartridge to try; I also ordered some 10 micron cartridges to try
2. Hose between filter and pump is clear. With 5 micron cartridge, hose is collapsing and air bubbles are visible. Pump also makes noises and motor gets hot, shuts off.
3. Feed/drain valves from both permeate and sap totes are several inches above inlet on RO
4. See 5.
5. I ran the RO for a little while without the filter cartridge, running sap that had already been through the RO once. Ran perfectly--no bad noises from pump; no collapse of clear hose between filter and pump; no air bubbles in that hose. Much better volume.

I'm hoping the 10 micron cartridges or the 5 micron Purtrex cartridge can increase flow adequately on gravity. Running the RO without a filter cartridge while doing a permeate rinse doubles the flow through the pump from 2 gpm to 4 gpm.

[carls47807]

You could also get a stainless filter housing rated to 300psi and put it after the pressure pump. The prefilter itself should be fine as the pressure differential across the filter would be minimal (it wouldn't collapse).

Are you using a 10" or 20" filter housing?
What are your inlet and outlet port sizes? What size hose are you using, and is it an OD connection or is it going into a barb (what size is the ID of the barb?).

I would use a hose capable of withstanding suction. As soon as that hose collapses the problem is exacerbated.

[DrTimPerkins]

1. I have ordered Purtrex "fuzzy" 5 micron cartridge to try; I also ordered some 10 micron cartridges to try
2. Hose between filter and pump is clear. With 5 micron cartridge, hose is collapsing and air bubbles are visible. Pump also makes noises and motor gets hot, shuts off.
3. Feed/drain valves from both permeate and sap totes are several inches above inlet on RO
4. See 5.
5. I ran the RO for a little while without the filter cartridge, running sap that had already been through the RO once. Ran perfectly--no bad noises from pump; no collapse of clear hose between filter and pump; no air bubbles in that hose. Much better volume.

Two issues based upon your answers.

1. Your filter micron rating is too tight (tubing collapsing). Go to 10 microns to up the flow through the filter.
2. You have a leak in the feed line somewhere (bubbles). Eliminate that and you're likely to have fewer problems. Any amount of air getting in to the feed line can cause the pump to shut down.

[wmick]

I think that having a filter before your pump on a gravity fed system is a recipe for pump damage.... I do believe you will be cavitating your pump, either from the start, or after the filter starts to plug up.
https://www.csidesigns.com/blog/articles/what-is-pump-cavitation-and-how-to-prevent-it

Going without a filter will not be good for your membranes, so I think you have 2 options...

1. Install a feed pump before your filter.
2. Move your filter to after the pressure pump... IF your filter housing is rated for the system pressure.

[maple marc]

wmick, thank you for the very good article on cavitation. I've been wondering about cavitation in pumps, and that article provided a lot of information. And Dr. Tim, thank you for your suggestions. I had a chance today to run my RO with just permeate with a 10 micron cartridge installed. Bingo--my flow through the cartridge increased dramatically. In fact, the output of my Procon pressure pump with the new cartridge was not significantly lower than running without the cartridge. I got the 10 micron cartridge that looks like wound yarn. Claimed to have a higher throughput--which seems true.

Reading more about the Procon pump, I now understand why it's not completely happy with gravity feed. The pump website indicates that inflow pressure for the pump must be above 20 psi. Aha....I believe that the head pressure for a IBC tote elevated slightly above my RO input line is probably below 2 psi, and maybe less than 2 gpm. The pump is putting out 4.6 gpm with no valve pressure.

My season is over, so I have time to consider some options. For now, I see no sign of cavitation, as there are no air bubbles visible in the clear hose ahead of the pump, the hose is not collapsing, pump is quiet, and the motor is running cool. Maybe I got lucky and didn't damage my RO....too much :( Next season if I notice some issues I will probably install a shallow well pump ahead of the filter. I've read that placing the filter after the pressure pump has its own issues.

Many thanks,
Marc

[canaanmaple]

My season is over, so I have time to consider some options. For now, I see no sign of cavitation, as there are no air bubbles visible in the clear hose ahead of the pump, the hose is not collapsing, pump is quiet, and the motor is running cool. Maybe I got lucky and didn't damage my RO....too much :( Next season if I notice some issues I will probably install a shallow well pump ahead of the filter. I've read that placing the filter after the pressure pump has its own issues.

Many thanks,
Marc

this is what I think they use on the nextgen ro's as feed pumps to the procons. it will allow for expansion of another membrane also.

https://www.harborfreight.com/1-hp-portable-sprinkler-pump-1075-gph-63320.html

[DocsMapleSyrup]

I use the pump canaanmaple referenced above as my 2 post 4x40 with the procon 330 requires 30 psi. It works fine as a feed pump for the procon. I pump from my bulk tank through a 5 micron 4x10" filter then to the procon and have no troubles getting the pressure needed for the procon. No cavitation while running.