4x40 vs smaller 400 gpd membranes

[MajorWoodchuck]

I was wondering when it's best to switch from the smaller 400 gpd membranes to the professional 4x40 membranes?
I have two 400 gpd membranes now. Had a Aquatec pump but felt the volume was lacking at 100 psi. I got a brass Fluid o tech carbonator pump and 1/3 hp motor super cheap that seems to put out about 2 gpm with little drop even as pressures exceed 100psi. I ran this on my two filters at 150 psi with gobs of volume. Thinking I can expand by 4 more of the 400 gpd filters for $168. I see for a few dollars more they now have 500 gpd filters...has anyone tried these?
It seems like to get into a 4x40 filters run $200 and a housing adds another $100. It seems like the 4x40 is rated at about 2400 gpd which is the same as 6 of the 400 gpd membranes.
Are there other advantages to the 4x40 that I am not seeing?

[DRoseum]

I ran dual ROs, each with 5 x 500 gpd membranes on coronwater 8900 pumps. Loved it - worked awesome. Sounds like your pump would easily handle that set up.

[billyinvt]

Please correct me if I'm wrong but my understanding is the flow rating on the 400gpd is based on 40 degree water. Running sap cuts that about in half, and really cold sap makes it even slower. I'm running five 400gpd membranes and barely processing 35 gallons per hour when the sap is really cold.

[darkmachine]

I think most people would tell you it's all about the amount of sap you have and the time you have to processes. I have a 2 post 4x40 and if i don't have 200 gallons of sap I can't run it because i won't have enough permeate water to flush it when i'm done(unless I've saved some, which I learned to do the hard way). that's where your records come into play, how much sap did you process last season. There is a cost involved in the next size up, but if you build a single post 4x40 and you use something like a procon 330, you can easily add another membrane down the road. I know they are wonderful machines.... my boiling and RO work is done in the middle of the day, the RO runs while I boil, and when i run out of sap I clean up for the day, no sap sits over night. know what time it takes gives me a little flexibility too, if i want to do a social boil on a Friday night I can plan on that, i don't have to boil flat out all week long and then still have to boil Friday night into Saturday morning. I'm sure everyone will be helpful with their experience too

[DRoseum]

[QUOTE=billyinvt;409585]Please correct me if I'm wrong but my understanding is the flow rating on the 400gpd is based on 40 degree water. Running sap cuts that about in half, and really cold sap makes it even slower. I'm running five 400gpd membranes and barely processing 35 gallons per hour when the sap is really cold.[/QUOTE

Correct and 35 or 40 gph with that setup is spot on.