Check valves (also called non-return valves or NRVs) are automatic valves that allow flow in one direction and prevent backflow when flow reverses or stops. Selecting the wrong check valve type can cause water hammer, pump damage, reverse flow contamination, or valve failure. The two most widely used check valve types — swing check and dual plate check — look similar on P&IDs but behave very differently in service.
1. Swing Check Valve — How It Works
A swing check valve uses a single disc hinged at the top of the valve body. Forward flow pushes the disc open against a stop. When flow stops or reverses, the disc swings closed under gravity and backpressure.
- Simple, robust design — few moving parts
- Full-bore opening when disc is against stop — low pressure drop
- Disc closes slowly (gravity-dependent) — water hammer risk at high flow velocities
- Must be installed horizontally for proper gravity-assisted closure
- Best for low-velocity, moderate-diameter services
2. Dual Plate Check Valve — How It Works
A dual plate check valve (also called a wafer check, butterfly check, or double disc check valve) uses two spring-loaded half-disc plates hinged on a central shaft. Forward flow pushes both plates open; when flow stops, the spring rapidly closes the plates before significant backflow occurs.
- Compact wafer or lug design — very short face-to-face length
- Spring-assisted fast closure — dramatically reduces water hammer
- Can be installed horizontally or vertically (upward flow)
- Lighter than equivalent swing check — preferred for large diameters
- Slightly higher pressure drop due to central shaft and spring
3. Head-to-Head Comparison
| Parameter | Swing Check Valve | Dual Plate Check Valve |
|---|---|---|
| Design | Single hinged disc | Two spring-loaded half-discs |
| Closure Speed | Slow (gravity-dependent) | Fast (spring-assisted) |
| Water Hammer Risk | High in large sizes / high velocity | Low — rapid closure prevents backflow surge |
| Pressure Drop | Lower (full bore) | Slightly higher (central shaft + spring) |
| Installation | Horizontal only (standard) | Horizontal and vertical (upward flow) |
| Face-to-Face Length | Long (flanged body) | Short (wafer type) |
| Weight (large DN) | Heavy | Light |
| Pulsating Flow | Poor — disc chatters | Good — spring stabilizes disc |
| Sizes | DN 50 to DN 1200 | DN 50 to DN 1200 |
| Applicable Standard | API 6D, BS 1868 | API 6D, API 594 |
4. Water Hammer — The Critical Factor
Water hammer is a pressure surge caused by sudden reversal of fluid momentum when a pump trips or flow is abruptly stopped. A slowly closing swing check valve allows significant backflow before seating — creating a destructive pressure spike when the disc finally slams shut.
Dual plate check valves close in milliseconds due to the spring force, preventing meaningful backflow and virtually eliminating water hammer in most applications. This is why they are mandatory in many pump discharge lines and large pipeline systems.
5. When to Use Each Type
| Application | Recommended Check Valve |
|---|---|
| Large-diameter pump discharge (DN > 200) | Dual plate check valve |
| High-velocity lines (> 3 m/s) | Dual plate check valve |
| Vertical pipeline (upward flow) | Dual plate check valve |
| Space-constrained installations | Dual plate check valve (wafer) |
| Low-velocity, horizontal service | Swing check valve |
| Lines with pulsating flow (compressors) | Dual plate check valve |
| General water, steam, horizontal service | Swing check valve |
| Pipeline pigging required | Swing check valve (full bore) |
Novel Valves manufactures both swing check and dual plate check valves in carbon steel, stainless steel, and alloy materials — API 6D certified and IBR approved where required.
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