New reverse osmosis system. Flow rate seems low. Please advise

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Originally Posted by ditttohead

Ro tank pressure shoud be set to 6 psi empty. The only way to test the tank pressure is when it is empty of water. If anyone tells you otherwise, they are wrong.

Your RO systems pressure is directly affected by line pressure. Adding air to the tank will not increase pressure to the faucet. At least not for the first half gallon. It will only lessen the tanks volume. The permeate pump shoud be installed without an ASOV, or at minimum, a 90% ASOV.

The tube length is always of great concern to flow rate avaiability. It has to do with frictional loss and capillary restriction calculations. I would recommend running any RO line between the tank and the faucet in 3/8" if it is more than 10', 1/2" if it is over 20'.

Hope this helps.

FYI, the flow rate should be approximately .5 GPM if the system is operating properly. Most faucets will flow at approximately 1 GPM. The loss of flow from the posy filter, tubing length, etc. can drop you to the 1/2 GPM range. This is fine since contact time is key for the post filter to provide the best tasting water.

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Thanks for this information Dittohead, and thanks for everyone elses help too.
As you guys can probably tell, I am not a plumber or a water treatment pro as many here are. I am must a consumer trying to educate myself as much as possible.

1. I am pretty sure that there is an ASOV on this system, however, I will go and make sure. I'll check out the manual and call the dealer if possible.
2. I can measure the tube length from the tank to the faucet. I am pretty sure it is less than 10 feet though.

Another question, Do these things have a break in period? I just measured flow rate again today and it seems even better. Filled the same quart container in 23 seconds. I guess that is a little better than .5 gpm which according to you guys is pretty good.

RO units have their own pressure and it has nothing to do with the regular house pressure, regardless of whether it is a pump or city system. The flow rate is ALWAYS "low". It is a combination of the low system pressure and the small tubing size.

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Originally Posted by hj

RO units have their own pressure and it has nothing to do with the regular house pressure, regardless of whether it is a pump or city system. The flow rate is ALWAYS "low". It is a combination of the low system pressure and the small tubing size.

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I am not sure where you got this information. please allow me to correct it. This is a common misconception. FYI, I do training on this topic regularly and to many of the large OEM and distribution houses.

A standard RO design with an ASOV will shut off the system when it reaches 60% of line pressure. So.. an incoming pressure of 60 PSI will = a maximum ro water tank pressure of 36 PSI.

An RO with a Permeate pump will typically shut off at 96% of line pressure, so the same 60 PSI water will yeild 58 PSI of tank water pressure.

An RO with a proper ASOV will shut off at 90% of line pressure. So the same 60 PSI will yield a tank pressure of 54 PSI.

The air on the bladder will be equal to the water pressure, simple physics.

As the water is used from the tank, the air pressure pushes out the water and as the air decompresses and loses pressure, so does the water pressure out of the tank. Simple physics, equal pressures...

The only exception to this would be an RO system with a booster pump. The booster will typically pump the water to 60-80 PSI depending on the internal bypass setting, then, regardless of incoming pressure (assuming ou have adequate flow) the system will produce the same amount of water reagardless of incoming pressure. Booster pumps are not needed for most smaller resdiential style systems, and should be avoided if possible. They are necessary sometimes due to excessive tds, lower temperatures, low incoming pressures, or a combination of these problems, but in general, are not needed.

Quote:

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Originally Posted by ribs1

Thanks for this information Dittohead, and thanks for everyone elses help too.
As you guys can probably tell, I am not a plumber or a water treatment pro as many here are. I am must a consumer trying to educate myself as much as possible.

1. I am pretty sure that there is an ASOV on this system, however, I will go and make sure. I'll check out the manual and call the dealer if possible.
2. I can measure the tube length from the tank to the faucet. I am pretty sure it is less than 10 feet though.

Another question, Do these things have a break in period? I just measured flow rate again today and it seems even better. Filled the same quart container in 23 seconds. I guess that is a little better than .5 gpm which according to you guys is pretty good.

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The systems should be allowed to fill and be fully drained 2-3 times for the first day. After that they are ready for use. Per the membrane manufacturers literature, the membrane does have a 72 hour start-up/wetting time. This is for critical applications where the 99.2% rejection rates are checked, regulate, and monitored, like for USP or WFI installations. For resideantial, 24 hours is fine.

If the system has an ASOV, make sure it is a 90% ASOV, not the standard 60%. The company you purchased it from should know which one they use. The 60% makes no sense and takes away the primary function of the Permeaterpump, high available water pressure, and more water volume in the tank.

The inventor of the permeate pump personally recommends no ASOV. The only time an ASOV should be used with a PP is when there is very low water usage. This can be countered by simply using more water, or purging the system weekly. Most residential applications use plenty of water for a PP.

Hope this helps.