10 Tips for Selecting a Miniature Check Valve

1. Choosing a Cracking Pressure

Choosing a check valve cracking pressure close to but below the full flow pressure of the system design is key. Full flow pressure is created by normal operating conditions and should be higher than the cracking pressure. This choice ensures the check valve opens fully and provides maximum flow when needed.

Check valves with flexing rubber sealing elements

Flexing diaphragm, duckbill, and umbrella check valves rely on the physical properties of elastomers to create resistance to downstream flow. Engineering this cracking pressure involves selecting the elasticity of the elastomer, the amount of squeeze applied when assembled (seal preload), and the rubber's thickness in the section of the valve that flexes.

The particular case of duckbill check valves

Duckbill check valves are ideal for low pressure, low flow applications, such as medical tubing sets, because they:

• Seal around trapped solids
• Have very low resistance to flow
• Have very low cracking pressures
• Provide tight reseal at low flow rates and low differential pressures

2. Maximum Working Pressure

Maximum working and backflow pressures

Internal media pressures and external environmental pressures affect check valve performance. Make sure the manufacturer's recommended operating pressure range, maximum backflow pressure, and burst pressure suit your application.

Maximum operating pressure is the internal pressure a check valve faces during normal conditions. It's also essential to know the maximum backflow pressure expected in the application. The internal mechanism has limits to the backpressure it can handle without damaging internal parts. A check valve's burst pressure will be higher than both its maximum backflow and operating pressures.

3. Maximum and Minimum Operating Temperatures

Media and environmental temperatures affect check valve performance. Choose a valve with a known working temperature range suitable for your application because internal components might be made of different materials than the valve body. Many metal check valves use rubber seals, and all polymers have higher thermal expansion coefficients than metals.

4. Reseal Pressure

Reseal pressure, spring-loaded check valves, and bubble-tight seals

Spring-loaded check valves can provide a positive seal and often reseal at pressures below the cracking pressure. For a bubble-tight seal, ensure the cracking pressure and system backflow pressure together are enough.

Low-pressure applications and reseal pressure

Spring-loaded check valve reseal pressures tend to be about 20% lower than their cracking pressure. For low-pressure applications needing bubble-tight seals, consider two spring-loaded check valves in series, known as dual or double check valve backflow preventers. This setup essentially creates a reseal pressure of 0 PSI across the valves.

5. Body and Seal Materials

Check valve components could include seal, body, spring, valve seat, connections, and sealing element. Ensure all components are compatible with the fluids or gases.

Metal versus plastic check valve bodies

Metal check valves:

• Higher burst pressures
• Lower thermal expansion
• Greater stress resistance
• Better shock pressure resistance
• Able to handle higher temperatures

Plastic check valves:

• Lower cost
• Lighter weight
• Longer service life
• Less prone to leaking
• Better corrosion resistance
• Better resistance to cavitation
• Broader chemical compatibility

6. Flow Capacity and Efficiency

Check valve flow capacity

Flow capacity is the volume that can pass through a check valve at a minimum pressure to open it fully. Oversized check valves create unnecessary pressure loss and wear on internal parts. Undersized valves restrict flow and reduce efficiency. Choose a valve that allows the system’s maximum required flow rate when between 20% and 80% open.

Check valve flow efficiency

The flow path and surface smoothness inside the valve affect flow efficiency. Optimized flow paths improve efficiency. Plastic check valves generally have smoother inner walls than metal ones. Choose the valve with the highest flow coefficient (Ck or Kv) for the lowest pressure drop. Practical flow calculations are recommended for proper valve sizing. You can also request samples to optimize system performance.

7. End Connection Types

Common miniature check valve connection types include push-in, threaded, hose barb, luer taper, and compression. Many series offer mix-and-match combinations like hose barb by thread.

Threaded connections

NPT and UNF threaded connections are often offered in male by male, female by female, and male by female combinations. UNF threads require rubber gaskets or O-rings for leak-tight seals. Ensure the thread types match for both mechanical strength and leak-tight connections.

8. Check Valve Orientation

Spring-loaded check valves

These can be used for horizontal and vertical installations because spring force, not gravity, closes the valves. Consider the fluid's weight above the valve in vertical installations when selecting cracking pressure. Upward flow adds to the spring's force, and downward flow works against it.

No-spring check valves

Generally intended for horizontal installation, they can be used in vertical installations if gravity on the sealing element creates a proper seal, but likely not bubble-tight. The fluid's weight above the valve affects cracking pressure and reseal quality in liquid handling applications. For more information on miniature check valve applications, Check now.