Back pressure in reverse osmosis water treatment or RO Plants describes a circumstance, in which the pressure on the feed water side is higher than the pressure on the product water side.

Let us get some idea of the back pressure in RO Plants and its prevention measures.

Why does back pressure occur in RO Plants?

The open side of a rolled membrane element is connected to a product water centre tube with an open hole, resembling a long, envelope-like membrane pocket. Multiple membrane pockets are woven onto a single product centre in such a way, that the feed water stream passes through the membrane's outer side, allowing fresh water to pass through the membrane into the pockets, and subsequently condense under feed water pressure into the product water centre tube.

A fabric support layer for product water infusion is sandwiched inside the membrane pocket's envelope-shaped structure, to facilitate product water flow. A spacer layer is sandwiched in the feed water channel between the membrane pocket, to cause the feed water to flow unevenly over the surface of the membrane pocket, and to disturb the water flow.

A bonding agent is used to join the membrane pocket's three sides.

Reverse osmosis systems/RO Plants cannot have back pressure because if the pressure on the feed water side is higher, than the pressure on the product water side, these bonding lines will rupture and cause a loss of desalination rate or a significant reduction in the membrane element.

Since, RO membrane filtration is pressure-driven, thus, there is no back pressure during normal operation. However, if the system is shut down normally or in the event of a failure, the valve is not set or opened properly, and there may be back pressure.

How is back pressure created in RO Plants?

Reverse osmosis membrane technical manuals typically have back pressure limit specifications, which assume the highest back pressure that the membrane can withstand is 0.1 MPa, or approximately 1 bar, equal to the pressure created by 10 m of water column.

The water in the production pipe will inevitably create a certain pressure when reverse osmosis is shut down, and the higher the production pipe climbs, the higher the pressure will be. If the production pipe climbs higher than 10 metres, then the back pressure on the water production side of the water production, will be sufficient to damage the membrane.

How is back pressure prevented in RO Plants?

1: The production pipe should have a check valve fitted to prevent pressure from being created by the water in the production pipe, and the reverse osmosis design procedure should define 8 metres as the production pipe's maximum ascending height.

2: The installation of an evacuation pipe after the production pipe's check valve can be used in situations, where the check valve is not strict or where the climbing height of the pipe must be high, to prevent the creation of back pressure.

3: Operational mistakes lead to the generation of another sort of back pressure, if the reverse osmosis process is performed incorrectly. The system pressure will increase, the pressure on the side of the water production will increase, but no water will be generated if the water production valve and water discharge valve are not opened, to switch on the pump.

4: The UPVC water production pipeline is typically made, and if the pressure is too great, it could rupture and result in a safety accident. When the operator opens the production valve to release pressure in an emergency, accidents can be prevented.

5: If the operator chooses to stop the pump, the pressure on the inlet side will quickly drop and the pressure on the production side would rise, damaging the membrane right away due to the high back pressure. As a result, designers must also take this into account when designing. If the bursting pressure of the membrane is 0.3 MPa, a bypass can be added to the side of the discharge valve, and a bursting membrane can be installed on the bypass.

6: Once the system is under pressure, the pressure on the water production side will automatically burst, and release pressure when the pressure exceeds 0.3 MPa to stop further losses. So make sure you adhere to the guidelines and do accurate bursting membrane studies.

7: In order to prevent back pressure accidents, water treatment equipment site commissioning personnel should also pay attention, to the reverse osmosis device operation process. Before starting, remember to verify that the water production valve and the production and discharge valve are both open.

If you want to get high-quality RO plants, call Netsol right away!

Netsol Water is a corporation with our roots in Greater Noida, India. We have been offering India's top Commercial RO Plants for many years. Thus, we are delighted to offer you field services as well as assistance with your choice of treatment products, in addition to providing comprehensive system design and engineering. To find out more, get in touch with us at +91 9650608473 or enquiry@netsolwater.com