Membrane Washing: Flushing versus Backwashing

[CharlieVT]

In reading posts on this site regarding membrane washing, I occasionally see folks use the term "backwash". I wonder are they actually backwashing their membranes, or using the term "backwash" when they actually mean "flush".

Definitions: Backwash: clean (a filter) by reversing the flow of fluid through it.
Flush: cleanse by causing large quantities of water to pass through it.


Question: Do some Reverse Osmosis machines actually have plumbing set up for backwashing? This would require that the wash fluid (permeate) be pumped through the RO in reverse of its normal direction, that is pumped into the normal permeate output line.

My assumption is that backwashing would be a more effective method of membrane maintenance than is flushing. Why are many (all?) commercially available RO units not set up for backwashing? Is it just the cost of the additional plumbing and valves? Or is there something about the membranes that makes backwashing inadvisable?

If this has been discussed previously, someone please refer me to that discussion; my search didn't find it.

Thanks for any replies,
Charlie

[maple flats]

I can't speak for other makes, but my owner's manual calls it backwashing, but it does not reverse the flow, it is just being flushed. One thing that does happen in the beginning of a "backwash" is that most of the sugar is washed to your concentrate tank. I suspect that is where the misnomer backwashing originated. You are washing a high percentage of sugar back where you want it, where it can be made into syrup. By the way, my RO is a Deer Run by Ray Gingerich, a basic RO.

[Clinkis]

Membranes are not designed to be back washed. They have a brine seal in them which is designed to have the flow/pressure on one side and in one direction. I would think that back washing could potentially compromise this seal. I would assume when they are talking about backwash they really mean flush.

[Sugarbush Ridge]

"when they are talking about backwash they really mean flush." When flushing,,, backwash you run the consecrate valve almost wide open to get maximum flow thru the membrane with very little going to permeate line. That washes sugar off the membrane and 'flushes' out any other stuff,,,,, only the special soap,,, acid and off season storage

[CharlieVT]

You gotta love those spell/autocorrect errors: "... you run the consecrate valve almost wide open..."
So that's how to get the sacred syrup, run the consecrate valve wide open. :lol:

Seriously, thanks for all the replies, Gents. The conclusion seems to be that no one is really "backwashing"; the word has just crept into the terminology of RO membrane flushing.

[maple flats]

Amen to that!

[OGDENS SUGAR BUSH]

when people start using the wrong terms its impossible to know what they mean

[Rockport]

Thanks Guys for the jibber jabber ,.... Really ... I was just thinking about this the other day and was going to ask, have been debating on doing a flush .. and seeing if the membrane is ok.