RO pump selection

[DapperTapper]

I'm a little confused about pairing the right pump GPD with an RO unit's GPD, can anyone help as I need to make an order by the end of the day...

My RO unit is capable of producing around 700GPD, but I only have 200-250GPD to process, maximum.

I am curious to buy the Aquatec (6800 or 8800) as almost everyone uses them here, but I'm struggling to find one in the UK I can get on next-day shipping.
What are people's opinions of the Z-Chen pumps?
And more importantly, which GPD shall I go for? Shall I match my batch size or try to meet the 700+GPD of the RO unit with the biggest pump I can find? (Currently 400GPD)
Will the 400GPD be too much?

[barnbc76]

I have the aquatech 8800, w/2-400gpd membranes. It works good for me. Are you saying you have 200-250gal of sap per batch, But you have 700gpd membranes or multiple membranes that equal up to 700? I dont recall all the specifics on how these things work but I can tell you for me I do about 60-100gal/batch and cycle it to about 7%. Not sure if that helps. I seem to remember something negative about the reviews I saw about auquatec 6800, can't recall.

[DapperTapper]

I'm dealing with an all in one unit (The Pentair PRF-RO), membranes are rated at 350 each (2 membranes, 1 pre-filter - I am also installing a 5 micron filter after the pump and before the RO), specified total GPD for the whole unit is 748 (Pure/permeate) GPD.

Operating pressure for the PRF-RO is between 40 & 80 PSI (Apx 2-5bar), I just can't seem to get my head around calculating if the 400GPD pump is going to be too much, or not enough with the 200GPD.

With low sap temps, the 5 micron filter, and back pressure (flow restrictor) the 400GPD should bring me within range.

Can these type of pumps be run on a variable supply?

[eustis22]

barnbc, how long does it take to cycle thru one of your batches, how many gph are you processing?

[DapperTapper]

Updates after speaking to a pump & RO specialist in the UK (Vyair.co.uk)

I learnt a large amount from this phone call...

I'm glad I didn't buy a Z-chen 400GPD, as it needs apx 7m of head height to even operate (without grinding itself down) - the 400GPD is just not going to cut it on a 750GPD RO system, especially with a 5 micron sediment pre-filter.

I'm not sure of the brand, (although it's not aquatec) but we (he, mostly!) decided that because of my demands (up to 1000L tank, with no mains pressure, 2m+ draw from the tank, 5 micron pre-filter + RO filters) that he could supply me with a similar quality pump that will transfer 5L(~1Gal)/min more importantly, at the right pressure of 80psi max. With the series membranes and their 350GPDea limit, it may well fall short of 80psi, but as that's my RO's maximum psi, I think he's right.

So this setup WILL process 750GPD (probably next year!) and will cope with my 250GPD in what he reckons will be less than 1 hour.

He also demands that the 5 micron MUST be put after the pump, or it may stress the pump so it too eventually grinds itself out because of insufficient flow - he did say that inline, pre-ro sediment filters of 100 micron up, fitted before the pump on this kind of system may not stress the motor, but he wouldn't like to try it.

That's the pump and RO specialists opinion, what about sap suckers' opinions?
(I am still trawling through RO and pump posts, so much to read!)