water testing and psi

[Tran901]

i just bought a h20 science ro/di water maker and i was wondering is there a way i can test the purity of the water? and what is a safe psi to run the unit at...i did it today from my bathroom sink at 55psi

the company said that it made 150gpd and according to my calculations at 55psi...it made about 120 gpd....i guess thats not too bad..

 

[rock_lobster]

Yea, just get a cheap TDS meter. Handhelds are 15$ usually

 

[AZDesertRat]

You should not own a RO/DI without having a handheld TDS meter, its the only way you have of knowing if its working or not.
RO membranes function well between 50 and 100 psi, 80 to 90 is best as it not only makes more water but also higher quality water too.

One word of caution, DO NOT try to mix or temper hot and cold water together to warm the water going to the membrane, this is the quickest way there is to ruin a membrane. they absolutely cannot take water over 113 degrees F and your hot water is probably much hotter than that. Remember being in the shower and someone flushes the toilet or starts the clothes washer? You got scalded, and thats the same thing that happens to the membrane which melts the glues that hold the membrane fabic together.

 

[Tran901]

thanks guys for the input...i am going to pick one of those up today and test the water.

i have it hooked up to my bathroom sink and at full blast it only goes up to 60-65...so will try that with my tds sensor

 

[AZDesertRat]

60 to 65 is good.
When you get the TDS meter you will want to test the water from three different points to determine how well the RO/DI is working, or what they call its rejection rate or removal efficiency.
1. Test the tap water TDS straight from the tap.
2. Test the RO only water beofre it gets to the DI. This may require either disconnecting the 1/4" line from the RO membrane to the DI cartridge or temporarily removing the DI cartridge from the housing so you get RO only.
3. Test the final RO/DI TDS.

The RO by itself should be removing 96-98% of the tap water TDS and the final or RO/DI TDS should be 0 or very close to it. When you start to see anything other than 0 TDS from the DI its time to change the DI cartridge or resin as spent DI resin releases trapped substances like phosphates and silicates which are weakly ionized, don't wait too long or you can have a disaster on your hands.

 

[firsttime]

60 to 65 is good.
When you get the TDS meter you will want to test the water from three different points to determine how well the RO/DI is working, or what they call its rejection rate or removal efficiency.
1. Test the tap water TDS straight from the tap.
2. Test the RO only water beofre it gets to the DI. This may require either disconnecting the 1/4" line from the RO membrane to the DI cartridge or temporarily removing the DI cartridge from the housing so you get RO only.
3. Test the final RO/DI TDS.

The RO by itself should be removing 96-98% of the tap water TDS and the final or RO/DI TDS should be 0 or very close to it. When you start to see anything other than 0 TDS from the DI its time to change the DI cartridge or resin as spent DI resin releases trapped substances like phosphates and silicates which are weakly ionized, don't wait too long or you can have a disaster on your hands.

Very good info. Did not know that, thanks.

 

[Y-Diver]

Is there a way to increase the pressure running through the unit? I am not getting quite enough PSI through the unit causing it to not be 100% effective....

Thanks,
Tyler

 

[AZDesertRat]

An RO membrane will never be a 100% efficient device and thats why we add DI resin to the end of the process.
Membranes will work from say a low of 40 psi to well over 150 psi, the upper limitation is the housings and fittings not the membrane whiich should stay below 100 psi.

If you know your homes pressure is borderline, simple things you can do to help the situation are use good quality prefilters and carbon blocks and change them frequently to keep pressure drop through the filters at a minimum. Plugged or fouled filters can cause a significant drop in pressure available to the membrane. Always use a prefilter with the same micron rating as the carbon block and only use a single carbon block, I prefer 1 micron or less for both. A plugged or fouled prefilter can be easy to spot in a clear housing but with many of the factory filters the micron size of the prefilter is 10 microns or more which makes the carbon block act as a secondary prefilter and they are harder to spot when it comes to plugging or fouling. A properly sized prefilter removes the suspended solids and colloidal materials before they reach the carbon so it can function as intended for removing chlorine and volatiles. A pressure gauge on the membrane housing or between the carbon block and membrane is a good tool here. When the flowing pressure drops a few psi change the filters, even if it has not been 6 months.

Another thing very often overlooked is monitor and correct your waste ratio. Most RO and RO/DI units come with a fixed flow restrictor which is non adjustable. The problem here is we do not all have the same water quality, pressure or temperature so our actual waste will vary.
You want to keep your waste ratio in the 3:1 to 4:1 range, 3 if you have very good tap water TDS to begin with and 4 for the rest of us. With fixed restrictors I usually find they are wasting 6:1 or more and you are losing pressure down the drain. Adjust that back to 3 or 4:1 and you gain several psi to the membrane which makes the unit perform better and produce more GPD. This can be done with a capillary tube flow restrictor you trim for your exact conditions or with an adjustable restrictor which usuallky incorporates a needle valve you squeeze down until you get the desired waste stream.

Some homes may have a pressure regulator on the incoming plumbing. Newer building and plumbing codes address pressures on your plumbing and some municipalities require the contractor install a regulator to reduce your pressure. If you have one its usually close to where your water meter and main house valve are located and can be easily adjusted with a crescent wrench or screwdriver.

If you have a drinking water system with a pressure tank you can look at what is called a "permeate pump". You MUST have a pressure tank though so for most reef RO/DI systems these will not work. You install it so it uses the waste stream to help power water through the membrane and they work quite well for those applications.

If all else fails and you just don't have sufficient pressure there are always booster pumps such as the Aquatec 8800. There are others out there but none has the proven reliability and track record the AquaTecs have, they have been around for years and years. Be careful when pricing booster pumps as some do not include the 24v DC power supply or a pressure switch which add to the cost so make sure you are comparing apples and apples.