What is The Flow Restrictor For?
Firstly, to create pressure throughout the membrane element. Secondly and more importantly, to maintain a desired ratio of reject flow (to drain) and permeate (product) flow. Residential membranes require a reject flow rate of at least 3-6 times the product flow rate. Normally this ratio is maintained at approximately 3:1 to 5:1. Therefore, a membrane rated at 10 gallons per 24 hour day should be sized with a flow restrictor of at least 50 gallons per day. Under-sizing the flow restrictor in order to run the system at higher recoveries results in premature scaling of the membrane, and shorter membrane life, and/or an increase in higher-TDS product water. Additionally, scaling of the flow restrictor will alter the flow rate to drain, and decrease the ratio, causing the above problems. To avoid this, flow restrictors should be changed regularly. The flow restrictor should be changed every time the membrane is changed. Flow restrictors are rated by a flow rate expressed as millilitres/min
