R/o woes

[jimbeaux]

Went to wash and found r/o system was discharging mainly reject water and very little spotfree water. Pump discharge was only about 60# of pressure. We figured membrane had failed so ordered new membrane and installed. Worked good for about a week and then had another failure. By this time we figured the membrane was probably good and the pump was going bad. Replaced pump, NO CHANGE. Now I have a spare pump.

SPECIFICS

Incoming water is 40 grains of hardness, After softener hardness is zero
No chlorine showing up after going through carbon filter
Membrane installed with flow of water correct
Prefilter clean
Removed membrane and have good water flow

Conclusion
Membrane is bad again but the question is WHY!
What am I overlooking?
Any help is appreciated. Thanks

 

[dogwasher]

Incoming water very cold? I know the cold water lowers the volume

 

[MEP001]

Many RO systems have a flush that opens a solenoid to the drain. Yours could be set to flush more often than needed or the solenoid could be sticking open. Membranes don't fail suddenly, they clog over time.

 

[Greg Pack]

I would look for a cause of "lack of back pressure". That's my own broader term there, but as MEP suggested, it could be coming from a partially open flush valve.

Essentially, somewhere there may be a way that too much water is escaping the reject plumbing for the system to maintain adequate membrane pressure. Some systems have a recirculating valve that could be open too far. Some (such as my pur-clean unit) have a needle valve on the reject that could have gone bad, allowing too much water to pass through. Find the ultimate reject line and partially occlude it where reject drops to closer to what it should be, and see if the system pressure rises.

 

[Bob-O]

Had the same thing happen to me last month. Just like MEP said, the reject solenoid was stuck open. Replaced the inner parts of the solenoid, so far no more problems....

 

[jimbeaux]

Thanks for the good replies. The water temp is relatively warm and the r/o system has no reject solonoid to stick open. We have a manual valve to adjust/balance the flow and it seems to be working fine. We double checked the hardness and chlorene levels and they haven't changed.
Any other ideals?
Thanks

 

[MEP001]

What size is the membrane? What pressure is it running?

Check your prefilter and see if there's an unusual amount of stuff on it. I recall someone who had a problem with membranes fouling quickly because the city was purging rust from the lines. He installed an extra-fine (.35 micron) prefilter and had no more membrane problems.

 

[DPD36]

I had a similar issue a year or so ago. Mine turned out to be the pump itself. For whatever reason it would pump at 190 or 200 psi for a day or two then at 60 or 70 psi. This gradually got worse to where the pressure never got over 60 psi. After replacing the membrane and checking the solenoids, valves, and electrical I finally took apart the pump. The discs that are furthest from the motor had started to fail. I talked to a tech at Flint and Walling and he told me that this is usually a sign of the pump being dead headed or run at too high of a pressure. My system prior to this ran at about 220 psi going into the membrane. I talked to an engineer with the company that built my RO system and he said that the 2 horsepower 16 stage pump was overkill for a single membrane system. I never got an explanation as to how it could intermittently provide good pressure. I replaced it with a 1.5 HP 12 or 14 stage and now run about 190 psi going into the membrane.

 

[PaulLovesJamie]

Check your prefilter and see if there's an unusual amount of stuff on it.

+1
I have a carbon tank (pre-filter), then a sediment prefilter. When I changed the carbon in the tank a few years ago, a few weeks later the RO pressure was too low to generate. Turns out there was quite a bit of dust in the new carbon that clogged the sediment prefilter. Replaced that filter (again) and everything was fine.

 

[PaulLovesJamie]

the r/o system has no reject solonoid to stick open.

Is there a solenoid for the backflush cycle?

One way or another, you are either not getting enough pressure on the inlet side, or you are losing pressure on the outlet side.

Try bypassing all your filters coming in to identify whether it is inlet our outlet, then you are half way there.

 

[mac]

Have you replaced the O rings in the end caps? We have started doing this anytime we do a membrane as it's cheap, and the O rings eventually fail.

 

[MEP001]

Failed o-rings on a membrane would make the pressure drop but would appear to make much more RO - it would be water bypassing the membrane and going straight into the tank.

 

[jimbeaux]

PaulLovesJamie,
The only solonoid on the system is the one that starts the pump to make r/o water.
We have removed the membrane from the system and using the pump to keep the r/o tank full. The pump is pumping plenty of water while going through the prefilter, which has only been in use for a couple of weeks. I guess it would be wise to change the prefilter again just in case.

 

[Greg Pack]

PaulLovesJamie,
The only solonoid on the system is the one that starts the pump to make r/o water.
We have removed the membrane from the system and using the pump to keep the r/o tank full. The pump is pumping plenty of water while going through the prefilter, which has only been in use for a couple of weeks. I guess it would be wise to change the prefilter again just in case.

Kill power to the pump. It should still keep it full.

Don't let that membrane dry out.