The “ heart“ of the NF/RO membrane system—“high pressure pump“

The high-pressure pump is one of the core equipment in the reverse osmosis system. The high-pressure pump provides sufficient pressure for the raw water entering the reverse osmosis membrane element to overcome the osmotic pressure and operating resistance, so that the device can maintain the designed waterflowwithout exceeding the maximum allowable inlet pressure of the membrane element.

There are many types and models of pumps on the market, how to choose?

For common nanofiltration and brackish water reverse osmosis membrane systems, high-pressure pumps generally choose centrifugal pumps; for seawater reverse osmosis systems, high-pressure pumps generally choose high-pressure centrifugal pumps or plunger pumps. The material of the high-pressure pump should be selected from different stainless steel materials according to the raw water.

The selection of high-pressure pump can be determined by calculation and simulation of design software to determine the design inlet flow and operating pressure of the reverse osmosis system, and then select a high-pressure pump with the appropriate flow and head according to the inlet flow and operating pressure. The head is generally reserved for 30% of the design margin. Because the working flow range of each specification of centrifugal pump is wide, two specifications of pumps with similar rated flow may meet the working flow range and working pressure range required by the system design at the same time. In this case, follow the system energy saving principle and select power consumption lower high pressure pump.

High-pressure pump starting method: install an electric slow-openingvalveat the outlet of the high-pressure pump or start the high-pressure pump with frequency conversion. The purpose is to avoid impact damage to the membrane element caused by instantaneous high pressure during startup (ie, water hammer phenomenon), and to ensure that the water supply pressure of the membrane element rises from zero to the rated value for more than 20-30s.

What are the measures to ensure the safe operation of high-pressure pumps?

In order to ensure the safe operation of high-pressure pumps, pump pressure protection devices are generally provided. That is, a low-pressure protection switch is installed at the inlet of the high-pressure pump to interlock with the high-pressure pump. When the inlet pressure is low (less than 0.05-0.1Mpa), the low-pressure protection switch will act to automatically stop the high-pressure pump to prevent the high-pressure pump from running dry. The outlet of the high-pressure pump can also be equipped with a high-pressure protection switch, which is interlocked with the high-pressure pump. When the outlet pressure of the high-pressure pump is too high (more than 30% of the maximum operating pressure), the high-pressure protection switch will act to make the high-pressure pump automatically stop running to prevent the high-pressure pump from being held up operation.