Backflow preventer

Product Overview

The Double Check Valve Backflow Preventer is an anti‑backflow device consisting of two independent check valves connected in series. It is designed to prevent low‑hazard, non‑health‑threatening media (such as slightly contaminated water, air conditioning water, industrial recirculating water, etc.) from flowing back into the upstream potable water supply system. Unlike reduced pressure zone (RPZ) backflow preventers that incorporate an intermediate relief chamber, the double check valve backflow preventer offers a more compact structure, lower pressure loss, and reduced maintenance costs, making it suitable for non‑toxic, non‑carcinogenic contamination protection. This product features flanged connections, with body materials limited to ductile iron or stainless steel, and a minimum nominal diameter of DN50. It is widely used in low‑risk backflow prevention applications such as commercial buildings, industrial cooling, irrigation, and fire protection systems.

Product Structure

The Double Check Valve Backflow Preventer mainly consists of the following parts:

1. Body: One‑piece or modular body made of ductile iron (QT450), stainless steel (CF8/CF8M), or gray cast iron. Flanged ends.

2. First Check Valve (upstream): Spring‑loaded lift or swing type, typically equipped with a rubber soft seal.

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

4. Spring Assembly: Stainless steel springs providing disc closing force and rapid response.

5. Test Cocks (standard): Test ports located in the chamber between the two check valves, as well as at the inlet and outlet, for field verification of each check valve’s sealing performance.

6. Air Release / Drain Valve (optional): For air removal before start‑up or draining during maintenance.

Compact overall length, light weight, and direct flanged installation onto pipelines.

Function

1. Prevents Backpressure Backflow: When downstream pressure exceeds upstream pressure, both check valves close simultaneously. The spring force combined with reverse pressure creates 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. Redundant Sealing Protection: Two independent check valves provide fail‑safe protection – even if one disc is slightly blocked by debris or its seal ages and leaks, the other stage maintains sealing, preventing backflow.

4. Low Pressure Loss Operation: With no intermediate relief valve, the water path is unobstructed; pressure loss is typically below 0.2 bar, suitable for continuous flow systems.

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

Working Conditions

1. Applicable Media: Tap water, air conditioning cooling water, heating hot water, industrial recirculating water, swimming pool makeup water, irrigation water, fire protection water, lightly contaminated water (non‑fecal, non‑toxic chemicals).

2. Temperature Range: 0°C to +80°C (standard EPDM seals); high‑temperature version up to +120°C (FKM or silicone).

3. Pressure Rating: PN10, PN16, PN25 (or Class 125, Class 150, Class 300).

4. Installation Position: Horizontal pipeline (recommended); vertical installation (flow upward) is possible provided effective spring closing is ensured.

5. Typical Applications:

   1. Makeup water lines for commercial building air conditioning systems

   2. Industrial cooling tower makeup pipelines

   3. Fire sprinkler system connections to municipal mains (low hazard)

   4. Landscape irrigation take‑off points

   5. Swimming pool and ornamental pond makeup water

   6. Boiler house auxiliary equipment makeup water

   7. Non‑direct contact process lines in food plants

Summary

    The Double Check Valve Backflow Preventer, with its series dual check valve redundant design, compact structure, low pressure loss, and in‑line test capability, is an economical and reliable choice for low‑health‑hazard (non‑toxic contamination) backflow prevention. This product features flanged connections, body materials of ductile iron or stainless steel, and a minimum size of DN50, making it suitable for medium‑ and large‑diameter pipeline systems.

    Compared with reduced pressure zone (RPZ) backflow preventers, it requires no discharge of water, avoids water waste, and eliminates the need for drain piping, making it more suitable for continuous pressure flow systems. Whether for air conditioning makeup water, cooling recirculating water, or fire protection auxiliary water, the Double Check Valve Backflow Preventer provides effective contamination isolation at low maintenance cost, meeting international and national backflow prevention standards. For pipeline systems that need to prevent non‑health‑hazard backflow, the Double Check Valve Backflow Preventer is an ideal core protection device.