What Makes Butterfly Valves Suitable for Both Clean Water and Raw Water Applications?

A Butterfly Valve is often described as a general-purpose valve for water service. That description is misleading. The same valve that performs flawlessly for five years in a treated water distribution line may fail in less than two years in a raw water intake that carries sand, silt, and debris. The difference is not the valve type. It is the material selection and the design details that determine how the valve handles the specific challenges of each water quality. This guide explains the differences between clean water and raw water service and how to specify a Butterfly Valve that performs reliably in both.

1. What Is the Difference Between Clean Water and Raw Water Service?

Clean water, also called potable water or treated water, has been filtered, disinfected, and stabilized. It contains less than 1 part per million of suspended solids. The pH is between 6.5 and 8.5, and the chloride content is low. Raw water, by contrast, is taken directly from a river, lake, or well. It may contain sand, silt, clay, organic matter, and biological organisms. The pH can vary from 5.5 to 9.0, and the chloride content can be high in coastal areas. The table below summarizes the key differences that affect valve selection.

In our factory, we have tested Butterfly Valve units in both clean water and raw water test loops. The raw water loop includes sand injection to simulate river intake conditions. The wear on the seat and disc is 5 to 10 times higher in the raw water loop than in the clean water loop. This is why the material selection must be different.

2. How Does Seat Material Affect Performance in Each Application?

The seat is the most critical component for sealing. In clean water service, the standard seat material is EPDM (ethylene propylene diene monomer). EPDM has excellent resistance to water, ozone, and aging. It operates effectively from -40°C to +120°C. In raw water service, EPDM is still suitable for many applications, but it can be damaged by abrasive particles. The particles become embedded in the seat and cause leakage. For raw water with high sand content, a harder seat material such as nitrile (NBR) or polyurethane (PU) is recommended. Nitrile has better abrasion resistance than EPDM, but it has lower temperature resistance. Polyurethane has the best abrasion resistance but is more expensive. The table below compares the seat materials for different water qualities.

Dafugui Pipe Valve Co., Ltd. manufactures Butterfly Valve units with all of these seat materials. Our factory recommends EPDM for clean water and nitrile or polyurethane for raw water with abrasive particles. We also offer a seat design with a stainless steel insert that protects the seat from abrasion while maintaining the sealing performance.

3. How Does Disc Coating Affect Durability in Raw Water?

The disc is the moving part that controls the flow. In clean water service, the disc can be made from ductile iron with an epoxy coating. The coating protects the iron from corrosion and provides a smooth surface that resists biological growth. In raw water service, the disc must resist abrasion from sand and silt. The epoxy coating can be worn away in high-velocity raw water, exposing the iron to corrosion. For these applications, we recommend a disc made from stainless steel or a disc with a hard chrome coating. The table below shows the disc options and their suitability for each water quality.

In our factory, we apply a hard chrome coating with a thickness of 50 to 80 microns on ductile iron discs for raw water service. The chrome coating has a hardness of 800 to 1,000 HV, which resists abrasion from sand and silt. We also offer a stainless steel disc for applications where corrosion is the primary concern.

4. How Should the Bearing and Stem Design Be Selected?

The bearing and stem are the components that transmit the torque from the actuator to the disc. In clean water service, the bearing can be a bronze bushing. Bronze has good load capacity and corrosion resistance in clean water. In raw water service, the bearing must resist the ingress of abrasive particles. A bronze bushing can wear rapidly if sand enters the bearing clearance. For these applications, we recommend a bearing with a sealed design or a self-lubricating bearing made from a polymer composite. The stem should be made from stainless steel to resist corrosion. The table below shows the bearing and stem options.

Summary for Valve Engineers and Maintenance Planners

Butterfly Valves are suitable for both clean water and raw water applications, but not with the same configuration. The seat material, disc coating, bearing type, and stem material must be selected based on the water quality. Clean water allows the use of standard materials such as EPDM and epoxy-coated ductile iron. Raw water requires more abrasion-resistant materials such as polyurethane, hard chrome, and polymer composite bearings. By specifying the valve for the most demanding condition, engineers can ensure reliable performance in both applications. Dafugui Pipe Valve Co., Ltd. has been manufacturing Butterfly Valve units for over 15 years and supplies to water treatment plants and industrial facilities worldwide.

Dafugui Pipe Valve Co., Ltd. manufactures Butterfly Valve units with EPDM, nitrile, and polyurethane seats, and with ductile iron, stainless steel, and hard chrome discs. We provide material selection guides and velocity calculations for water applications.