Backflow preventer

Product Overview

The Stainless Steel Low Resistance Backflow Preventer is a compact anti‑backflow device consisting of two independent check valves connected in series with no intermediate relief chamber. It is specifically designed to prevent low‑hazard, non‑health‑threatening media from flowing back into the upstream potable water supply. This product features a one‑piece (integral) body construction, flanged connections, and a minimum nominal diameter of DN50.

Compared with conventional brass or cast iron backflow preventers, the stainless steel version offers excellent corrosion resistance, high temperature capability, and a hygienic surface finish, resisting attack from many chemicals, acid/alkali solutions, seawater, and high‑purity water media. The product provides extremely low flow resistance (≤ 0.15 bar pressure loss at full open), no water discharge, and no water waste, conforming to EN 1717 (DC type) and ASSE 1015 standards. The stainless steel construction makes it particularly suitable for corrosive media, high‑purity water, and food/pharmaceutical applications where material integrity is critical.

Product Structure

The Stainless Steel Low Resistance Backflow Preventer (flanged, one‑piece) mainly consists of the following parts:

1. Body: One‑piece precision cast stainless steel body with no welded seams, available in CF8 (304), CF8M (316), or CF3M (316L). Flanged ends conforming to GB/T 9113, ANSI B16.5, EN 1092‑1, etc.

2. First Check Valve (upstream): Spring‑loaded lift or swing type check valve with a rubber soft seal (NBR/EPDM/FKM).

3. Second Check Valve (downstream): Same construction as the first, installed in series within the one‑piece body to provide dual sealing redundancy.

4. Spring Assembly: Stainless steel (304/316) coil springs providing initial closing force and rapid response.

5. Test Cocks (optional): Stainless steel test ports located in the chamber between the two check valves for field verification of sealing performance.

6. Integral Bonnet: Stainless steel bonnet cast integrally with the body or bolted, allowing easy maintenance and cleaning of internal cartridges.

All wetted parts are stainless steel or corrosion‑resistant alloy, with no copper or iron materials. The one‑piece design eliminates potential leak paths between flanges, offering a more compact and reliable construction.

Function

1. Prevents Backpressure Backflow: When downstream pressure exceeds upstream pressure, both check valves close simultaneously, using spring force and reverse pressure to create a dual seal, stopping backflow.

2. Prevents Backsiphonage: When upstream pressure drops sharply to a negative condition, both check valves close quickly, cutting off any siphon backflow from downstream media.

3. Low Resistance Operation: With no intermediate relief chamber, the flow path is unobstructed, and pressure loss is typically ≤ 0.15 bar, making it suitable for continuous flow systems with significant energy savings.

4. Redundant Sealing Protection: Two independent check valves provide fail‑safe protection – even if one disc slightly leaks, the other stage maintains sealing, preventing backflow.

5. No Water Discharge: Unlike RPZ types, this product does not discharge water during normal operation, resulting in no water waste and no need for drain piping.

6. In‑Line Testing: The sealing integrity of each check valve can be tested individually using the test cocks without removing the valve from the pipeline.

7. Corrosion & High Temperature Resistance: The all‑stainless‑steel construction resists acids, alkalis, salts, seawater, chlorides, and many chemicals, with a wide temperature range (–20°C to +200°C).

8. One‑Piece High Reliability: The integrally cast body has no intermediate flange sealing faces, eliminating external leakage risks and ensuring long‑term continuous operation.

Working Conditions (Focus: Stainless Steel Applications)

Why Stainless Steel is Required: In the following conditions, conventional brass or cast iron backflow preventers would suffer corrosion, rust, or media contamination, making stainless steel mandatory.

1. Applicable Media:

   1. Corrosive media: dilute acids, dilute alkalis, salt solutions, seawater, chlorinated water, chemical solvents

   2. High‑purity water: deionized water, reverse osmosis permeate, water for injection (WFI), purified water

   3. Food & beverages: fruit juices, dairy products, syrups, beer, CIP cleaning solutions

   4. Pharmaceutical water: process water, rinsing water

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2. Temperature Range: –20°C to +200°C (depending on seal material; stainless steel body can withstand higher temperatures)

3. Pressure Rating: PN10, PN16, PN25 (Class 150, Class 300)

4. Nominal Diameter: DN50 – DN300 (2″ – 12″); common sizes DN50–DN200

5. Installation Position: Horizontal (recommended) or vertical (flow upward)

6. Typical Applications:

   1. Chemical plant corrosive media makeup water lines (DN50 and above main lines, preventing acid/alkali backflow)

   2. Seawater desalination plant drinking water or process water outlets (resistant to chloride corrosion)

   3. Pharmaceutical purified water / WFI distribution systems (sanitary, contamination‑free)

   4. Food & beverage production line CIP cleaning circuits and raw material water makeup

   5. Electroplating plant deionized water makeup lines

   6. Medium/large laboratory high‑purity water systems

   7. Boiler chemical dosing lines (high temperature and corrosion resistant)

   8. Seawater cooling system makeup water intakes

Summary

The Stainless Steel Low Resistance Backflow Preventer (flanged, one‑piece), with its all‑stainless‑steel corrosion‑resistant body, series dual check valve redundant design, extremely low flow resistance, no water discharge, and one‑piece high‑reliability construction, is the ideal anti‑backflow solution for medium to large bore pipelines (DN50 and above) handling corrosive media, high‑purity water, and sanitary applications.

Compared with brass or cast iron counterparts, the stainless steel version resists long‑term corrosion from acids, alkalis, seawater, chlorides, and many chemicals, while providing a smooth, dead‑spot‑free surface that meets food and pharmaceutical sanitary standards. The one‑piece flanged design eliminates intermediate flange sealing points, offering more reliable installation, especially in demanding services such as chemical, pharmaceutical, food, seawater desalination, and high‑temperature water systems. For pipeline systems with corrosive, high‑purity, or high‑temperature characteristics and diameters of DN50 and above, the Stainless Steel Low Resistance Backflow Preventer is an indispensable safety component.