jdieck
New member
Carlo:
What controls the ratio of waste to product is not the membrane nor the amount you pump in but how much you restrict the waste. In other words it is the restrictor which for a given inlet pressure dictates how much water is wasted.
A single membrane working with an inlet pressure of 70 psi with a restrictor which is adjusted to produce a backpressure such as to force one gal trough the membrane and let 4 gallons pass to the waste will create almost the same back pressure and allow the same flow to the waste. I say almost because in the second case it will see a pressure of 64 to 65 psi rather than 70 due to the pressure drop from the first membrane to the second.
In round numbers the second membrane sees 4:1 because the restrictor will let pass 4 (as before with a single membrane) The first membrane sees 5:1 because it sees the 4 of waste that the restrictor lets pass plus the 1 that goes as product trough the second membrane.
In round numbers The inlet to the first membrane is 6, the product of the first is 1 and the waste of the first is 5. The inlet to the second membrane is 5, the product of the second membrane is 1 and the waste from the second is 4
Overall you input 6, produce 2 and waste 4 so in round numbers you gate on the overall a waste of 4:2 (2:1) rather than the 4:1 you will get with a single membrane.
Again as mentioned before these are round numbers and the ratio will vary depending on the specific membranes, TDS input, temperature and adjustments for discharge pressure of the booster pump, I have seen anything from 1.75:1 to 2.5:1
What controls the ratio of waste to product is not the membrane nor the amount you pump in but how much you restrict the waste. In other words it is the restrictor which for a given inlet pressure dictates how much water is wasted.
A single membrane working with an inlet pressure of 70 psi with a restrictor which is adjusted to produce a backpressure such as to force one gal trough the membrane and let 4 gallons pass to the waste will create almost the same back pressure and allow the same flow to the waste. I say almost because in the second case it will see a pressure of 64 to 65 psi rather than 70 due to the pressure drop from the first membrane to the second.
In round numbers the second membrane sees 4:1 because the restrictor will let pass 4 (as before with a single membrane) The first membrane sees 5:1 because it sees the 4 of waste that the restrictor lets pass plus the 1 that goes as product trough the second membrane.
In round numbers The inlet to the first membrane is 6, the product of the first is 1 and the waste of the first is 5. The inlet to the second membrane is 5, the product of the second membrane is 1 and the waste from the second is 4
Overall you input 6, produce 2 and waste 4 so in round numbers you gate on the overall a waste of 4:2 (2:1) rather than the 4:1 you will get with a single membrane.
Again as mentioned before these are round numbers and the ratio will vary depending on the specific membranes, TDS input, temperature and adjustments for discharge pressure of the booster pump, I have seen anything from 1.75:1 to 2.5:1