Why should a manual regulating valve be installed after the high-pressure pump in a reverse osmosis system?

The high-pressure pump plays a crucial role in reverse osmosis (RO) equipment, ensuring the smooth operation of pretreatment, reverse osmosis, water supply and withdrawal, and flushing. Therefore, selecting a durable pump is paramount in RO systems.

The high-pressure pump is closely related to water supply pressure. Initially, the system doesn't require high pressure to achieve the designed water output, resulting in excess pump pressure. However, over time, pump wear reduces this excess pressure, diminishing the RO system's efficiency.

So, how can this problem be solved?

Standard reverse osmosis water is virtually impurity-free due to the absence of membrane fouling. However, in practical applications, except for secondary RO systems using primary RO water as feed water, most RO systems use water that has undergone standard pretreatment. Although pretreatment removes some impurities, the feed water quality is still inferior to that used in standard testing conditions. Therefore, the membrane element's design water output should be less than the standard output. If the standard output is still used as the design output, the RO membrane elements will quickly become fouled, leading to damage.

Manufacturers select different design water outputs for membrane elements based on different feed water sources. However, membrane fouling is inevitable and will gradually occur with continued use. Chemical cleaning can partially restore performance, but complete restoration is difficult. Therefore, the design should use a water pump that can maintain the design water output after three years, requiring a higher-pressure pump.

To achieve this, a manual adjustment valve should be installed after the high-pressure pump to regulate water supply pressure, or a variable frequency drive (VFD) should be used to adjust the water supply pressure, ensuring the pump's longevity and achieving the desired water supply.

After installation, the manual adjustment valve usually doesn't require frequent adjustment and remains in a constant position for extended periods. Opening and closing this valve isn't necessary each time the system starts.

However, without another valve after the high-pressure pump, the high-pressure water source directly impacts the membrane elements upon system startup, especially if air is present, causing a 'water hammer' effect that can damage the membrane elements.

To prevent this, an electric slow-opening valve should be installed after the high-pressure pump. This valve slowly opens after the pump starts, gradually applying pressure to the RO membrane. It should be a fully open/fully closed valve with adjustable opening/closing time, typically set to 45-60 seconds. Therefore, an electric slow-opening valve should be installed for membrane element safety.