Question about water filters

[grrl]

My wife bought a water cooler/filter. It has a five-stage filter and according to the manual as part of the 2nd and 3rd stages dumps about 40% of all the water that goes into the system. There is a solenoid that controls the flow and it stays open so long as the holding tank is being filled.

I can't imagine why they would need to discard any of the water as part of the filtration process. What purpose could that possibly serve? Does anyone know?

 

[Mark R]

It may use reverse osmosis, in which case you have to lose some of the water.

A reverse osmosis filter works by using water pressure to force water through a semi-permeable membrane, leaving the solutes behind. However, the membranes are fragile and can only tolerate low pressures - as the source solution becomes more concentrated, the filtration becomes slower and slower. In order to maintain efficiency, the water needs to be refreshed.

 

[AbsolutDealage]

Originally posted by: Mark R
It may use reverse osmosis, in which case you have to lose some of the water.

A reverse osmosis filter works by using water pressure to force water through a semi-permeable membrane, leaving the solutes behind. However, the membranes are fragile and can only tolerate low pressures - as the source solution becomes more concentrated, the filtration becomes slower and slower. In order to maintain efficiency, the water needs to be refreshed.

Yes, this is definately a reverse osmosis filtration system.

If you are worried about the waste water, you can buy a kit that will pump the waste water back down into your hot water heater. The relative jump of impurities in your heater tank will be negligable, and you will not be wasting any water.

 

[jagec]

Originally posted by: Mark R
It may use reverse osmosis, in which case you have to lose some of the water.

A reverse osmosis filter works by using water pressure to force water through a semi-permeable membrane, leaving the solutes behind. However, the membranes are fragile and can only tolerate low pressures - as the source solution becomes more concentrated, the filtration becomes slower and slower. In order to maintain efficiency, the water needs to be refreshed.

welll....in order for reverse osmosis to work, the pressure differential has to be pretty darn high...so the membranes aren't as fragile as you'd think.

 

[grrl]

That is probably it, there is a pressure boosting pump on the inlet side. I'll check the output pressure on the label.

The manual suggests you catch the waste in a bucket (I live in an apartment with central hot water so can't pipe anywhere else but the washing machine) yet the problem right now is the solenoid is faulty so always leaks water. :disgust:

 

[DrPizza]

Originally posted by: grrl
That is probably it, there is a pressure boosting pump on the inlet side. I'll check the output pressure on the label.

The manual suggests you catch the waste in a bucket (I live in an apartment with central hot water so can't pipe anywhere else but the washing machine) yet the problem right now is the solenoid is faulty so always leaks water. :disgust:

wouldn't the solenoid simply control a valve? I've only closely worked with one such solenoid - it had a simple diaphragm to replace. (finding the replacement was hard) Replacing it took care of a leak - very easy to do.

 

[grrl]

Dr Pizza. The company came and replaced the solenoid, but it still leaks. You're right, a solenoid valve should either be open or closed, but either I've gotten two bad ones or they have designed this one to allow a little water past even after the reservoir is full and the pump is off (although I took the first one apart and don't see how).

jagec, the pump pressure is 100 psi and the cartridges are rated at 125.

 

[JediJeb]

There could be a constant flow there to regenerate the filter or to keep bacteria from building up. Our ultra pure systems in the lab have a recirculation cycle which kicks in every few hours to make sure there is fresh water on the waste side of the filter, maybe yours just uses a small constant flow. The company should be able to tell you if that is the case. Also there could be a small sand particle or something like that wedged in there that is causing it to leak, if the plumbing is older in the apartment then it could be hard water scale flaking off and sticking in the valve keeping it from closing completely.

 

[grrl]

Originally posted by: JediJeb
There could be a constant flow there to regenerate the filter or to keep bacteria from building up.

That seems to be the system, although the repair guy didn't explain it that way or suggest that the solenoid wasn't faulty because of it. By design it seems to constantly drain a little water through the filters. That sure wastes a lot of water. It woudn't be so bad if I could reuse the water but it fills up my washing machine every 24 hours!