[Mike_G]

Any advice gladly recieved. I am about to change the pre filter on my merlin for the first time (reading up from 11ppm to 39) Is it just a case of swapping the filters or is there more to it than that?

[cybersye]

Hi Mike,
I'm going to have to do the same soon,
hope it is that straight forward
Wheres best to buy replacement pre filter from and does anyone recommend adding an additional pre particle filter before the merlin, if so what? (I'm in a very hard water area 350ppm +)
cheers
Simon

[Mike_G]

Got mine from window cleaning warehouse £21.15 inc vat   Free delivery this month.

[JM123]

Hi Guys I'm just back in from the shopping centre cleans (have to do them during the night - its crazy but crazy I do).

The prefilter on the merlin should be changed every 19000gallons/3 months whichever is sooner.  You should backflush the membranes at the same time.  Other than that just be careful not to let any of the dirt off the prefilter get into the membrane inlet.

[freshwater]

The pre-filters primary job is to remove chlorine wich degrades the membrane letting more TDS through. Changing the pre-filter will reduce your TDS by a bit, but not back to the original level. As JM123 says 19,000 gallons (US) thats about 80,000 litres, and thas input not output so at the average ratio 1 pure to 4 waste thats evey 16,000 litres of pure. If you are using 300 a day, 5 days a week that 10 weeks.

Changing pre-filters is important it will prolong the life of your membranes, and in a Merlin youve got two them. Its cheaper to the pre-filter than the membranes or ro use extra resin. Ths goes for all RO systems.

[surecleansystems]

Hi Guys

Please check out link below, the carbon prefilter in the merlin needs to be changed every 19,000 litres not gallons

And as freshwater says thats input water so depending on how you have your merlin tweaked you need to be changing the carbon prefilter very regularly.

does anyone recommend adding an additional pre particle filter before the merlin, if so what? (I'm in a very hard water area 350ppm +)
cheers
Simon

Osmonics recommend if you are using the merlin for commercial purposes then a sediment prefilter is necessary. A 5 micron sediment filter is fine for the job.




http://www.gamurdock.com/gam/files/documents/MerlinBrochure.pdf

[JM123]

Please check out link below, the carbon prefilter in the merlin needs to be changed every 19,000 litres not gallons

does anyone recommend adding an additional pre particle filter before the merlin, if so what? (I'm in a very hard water area 350ppm +)
cheers
Simon

Osmonics recommend if you are using the merlin for commercial purposes then a sediment prefilter is necessary. A 5 micron sediment filter is fine for the job.

http://www.gamurdock.com/gam/files/documents/MerlinBrochure.pdf

very true art - sorry I'm mistyping everydind larteley, leeters insted of galions

[surecleansystems]

No problem glad to be of help

[Mike_G]

How exactly do you backflush the membranes?

[freshwater]

Mike,

Its not so much a backflush as a forward flush. Under normal use muck settles on the surface of the membrane, by allowing water to run to drain without restriction this flushes the membrane. I have never tried it on a merlin but I would asume you need the flushing tank/kit. I'll get one out of stock in the morning and have a play around with it and see if it can be made to flush without the flush kit.

We have Merlin pre-filters at £20 inc vat & carriage, and a 5microm polyprop pre-filter in a housing with 3/4" connections, spanner & bracket also at £20 inc vat & carriage.

steve@freshwatersystems.co.uk

[Mike_G]

Cheers Steve, just checked water going in and it is 436 so maybe 33 coming out is not so bad. I look forward to your results tomorrow

[thewindowcleaner1]

How exactly do you backflush the membranes?

Its not so much a backflush as a forward flush

I diconect the waste pipe from the merlin,shut off the water to the holding tank and turn on the water, and let it run for 15 minutes, this was sugested to me by some one from RO man apparently the waste water out let has a restricted flow and by diconecting it you alow the water to flush through, and yes change the pre filters as much as possible, I have an additional 30" pre filter and I still had to change the membrains after 12 months, and I ve heard rummers that this is common.
 On the briht side if you cost out replaceing membrains 12 months and prefilters 2months it cost out at around £5 to £6 per week (less than one house) well worth it

[freshwater]

Mike,

Thats no to bad on a Merlin with 400+ on the inlet side, I asume from your high TDS you are in a hard water area and the calcium & magnesium that make up the hardness are not the easiest elements to remove with an RO.

steve@freshwatersystems.co.uk

[freshwater]

thewindowcleaner1

I think the restrictor is built into the manifold (the big grey bit) and not into the tube as on a standard RO system. When I do the test on the flushing in the morning & will also have a look a the drain to see where the restriction is.

steve@freshwatersystems.co.uk

[JM123]

the merlin is built with a series of check valves in the manifold, when the product line is sealed off the permeate which has already gone into the tank is forced back over the membranes and out through the waste, think of it this way, when running the merlin some of the permeate goes into the pressure tank until equilibrium is reached (press same in tank as in merlin), when you block the product line and switch off the supply the check valves will allow the water in the pressure tank to blast back through thus flushing the membranes, hope you all got that ok!!

[freshwater]

Had a Merlin out today. The only restrictor I can see is the drain elbow on the manifold unless there is one in the manifold, so I don’t think just pulling pipe out will give a flush. However when I took the elbow out of the manifold I got a good flow to drain and reduced flow on the outlet. I will try the flushing mechanism in the morning.

Question for JM123 so its back flush or forward flush?

[JM123]

strictly speaking I think it would be considered forward flushing as the check valve stops the permeate water from re-entering product line although the water has already came through the membrane, if in any doubt check with GE

[freshwater]

Using the info provided by JM123 I put a vale on the output of a Merlin. Then I put a tee on the inlet and fed it through another valve to the connection for the flush tank. On turning off the outlet the check valves inside the Merlin (as JM123 described) shut off the inlet to prevent water running to waste. I the opened the pipe to the flush tank connection and the membrane flushed to drain. As the Merlin is designed for domestic used I assume this a good way to flush the membrane during down periods such as over night when no water is being used, and could be of benefit to those WFPs who only have the melin in used for a few hours a day, but if you are running your Merlin for a long period each day with only short periods shut down its probably not worth it.

steve@freshwatersystems.co.uk

[JM123]

hhmmm, generally we flush them by connecting the flushing tank to the 6mm connection on the manifold, once the merlin has ran for 10 mins we open the valve on top of the tank to allow permeate into the tank, we then close off the product outlet,  after another 5 mins the pressure is equally balanced between tank and system.  next we close off the inlet and the pressurised tank will force the water back through over the membranes and flush them clean.

or you could do it as freshwater says, I think, have to try it that way myself.

[freshwater]

JM,

It was just an exercise to see how it worked, personally if I was going to use the flush I would use the expansion vessel to do it automatically. I wouldn't sit there opening and closing a valve every hour or so, there's not much point in having it if its not automatic.

steve@freshwatersystems.co.uk