There are two main designs to consider when selecting a check valve for axial flow applications in piping systems (we also call it axial flow check valve). They are single-disc or poppet-type valves and double-disc check valves. Both types allow flow in one direction while preventing back-flow. However there are some key differences in their operation and suitability for various services that need to be understood.
How Single Disc Valves Work
In a single-disc check valve (also called a poppet valve), a circular disc or “poppet” rests against the orifice. Fluid enters axially around the disc, opening it from its seat. When reverse flow occurs, the valve disc drops and closes under the action of gravity or fluid force to prevent reverse flow.
Pros of Single Disc Valves
- Simple and economical design without springs or hinges.
- Compact inline footprint fits into tight spaces.
- Lightweight poppet responds quickly to flow changes.
- Low popping pressure opens easily with minimal headloss.
Cons to Consider
- Susceptible to disc bouncing at low flows or very rapid reversals.
- Prone to water hammer damage if used with rapidly closing valves.
- Minimal flow capacity – best for smaller pipe sizes.
- Disc can hang up on debris and not reseat fully.
Dual Spring-Loaded Disc Operation
The two adjacent discs in a double disc check valve are held closed on the valve body by a coil spring. On forward flow, pressure forces the discs apart as they pivot on pin hinges. Instead, countercurrent pushes them closed, and the increased pressure compresses the springs.
Benefits of Dual Disc Design
- Very positive closure, less sensitive to transient pressures.
- Higher flow capacities for larger pipe diameters.
- Less bounce and chatter than single disc wafer check valve.
- Springs help crush debris for reliable operation.
- Avoids disc corrosion issues with certain fluids.
Drawbacks of Dual Disc Models
- More complex construction increases cost.
- Larger physical size may not fit in tight spaces.
- Requires higher cracking pressure to open discs.
- Spring wear could reduce closing capability over time.
Overall, the single disc valve is a good budget choice for clean flow service or low pressure rise applications under 3 inches. However, dual disc check valve provides smoother operation and is suitable for higher flow rates, tighter containment requirements or debris handling in larger pipes. When choosing between two axial check valve types, please consider flow rates, fluid characteristics and installation space.