RO feed pumps

Larger feed-pump requirements, because the RO feed pump must now pressurize both the influent stream plus the recycled reject stream. As a result, the RO feed pump must be larger, which may mean higher capital for the RO system. 

Some vendors place both passes on a single skid, thereby eliminating the RO feed pump to the second pass RO. The backpressure from the first pass is sufficient to provide the applied pressure required of the second pass. Care must be taken so that permeate backpressure does not exceed the applied influent pressure to the first pass, or osmosis rather than reverse osmosis will occur. Additionally, high back pressure can lead to delamination of the membranes (see Chapter 12.1.2.1 and Figure 12.1)... 

An RO skid includes the pressure vessels in which the membrane modules are contained (see Chapters 43.3 and 6.3 for detailed discussions about pressure vessels). Skids also commonly include cartridge filters in a housing or housings and an RO feed pump, although combinations exist with just pressure vessels or pressure vessels with cartridge filters. Finally, there are included on the skid instrumentation and controls for the system. Figure 6.1 shows an RO skid with these components. 

An RO feed pump requires a certain volume and pressure of make-up water to the suction side of the RO feed pump so as not to... 

Deficient pretreatment design. If pretreatment equipment is designed to backwash with service water while the RO unit is on-line, allowances must be made so that enough flow reaches the suction of the RO feed pump while the pretreatment equipment is in backwash. 

Low influent flow—insufficient flow is available to keep the RO feed pump flooded and operating properly. 

Low influent pressure—this could lead to cavitation of the RO feed pump. 

Low suction pressure is typically a result of inadequate water supply to the RO feed pump caused by upstream demand starving the RO system. Upstream demands include filter backwash water and water diverted for other applications within the facility. Starving of the RO due to equipment backwashing upstream is a system design flaw. Diversion of feed water usually occurs during installation or... 

An RO feed pump requires a certain volume and pressure of make-up water to the suction side of the RO feed pump so as not to cavitate the pump, as discussed above. Low pressure and volume to the suction side of a pump are typically caused by one of the following three problems ... 

Under a typical single-stage SWRO system configmation, each RO train has a dedicated system of transfer pumps for pretreated seawater followed by a high-pressure RO feed pump. The high-pressure feed pump motor/operation is coupled with that of energy... 

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