HVAC Solenoid Valve Sizing

Key Takeaways

• Valve Types: Solenoid valves come in two types – direct acting (limited to small applications) and pilot operated (requires minimum 1 psi pressure drop)
• Sizing Critical: Never select solenoid valves based on line size alone – always size based on system capacity with minimum 1 psi pressure drop
• Pressure Drop Requirement: Pilot operated valves need at least 1 psi pressure differential to return to normal position after operation
• Connection Adaptation: Using bushings and couplings to adapt connection sizes won’t affect valve performance when properly sized

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Understanding HVAC Solenoid Valve Sizing

Obtaining reliable performance with solenoid valves on refrigeration or air conditioning systems demands careful consideration of application requirements during the selection process. Whether you’re working on a simple split system or complex commercial refrigeration equipment, proper valve sizing can make the difference between smooth operation and recurring service calls.

Sporlan offers a wide variety of solenoid valve sizes and styles that may be employed in refrigeration and air conditioning systems to control refrigerant flow electrically. These electrically operated ‘stop-valves’ are either fully open or fully closed – remember, they do not modulate flow like bi-flow TXVs in heat pump systems.

Two Basic Solenoid Valve Types

Solenoid valves are typically classified according to the stem and plunger action, and understanding these differences is crucial for proper selection:

1. Direct Acting Valves

Energizing the coil directly opens the main port of the valve, allowing full flow. A direct acting valve pulls the plunger against inlet pressure and is typically limited to small applications or where there is a low-pressure differential across the valve. These work well in low-capacity systems but struggle with higher pressure applications.

2. Pilot Operated Valves

Energizing the coil opens a pilot port which releases pressure above the main disc/piston/diaphragm, allowing it to move to an open position for full flow. A pilot-operated valve makes use of a pressure differential across the valve to allow for higher flow capacities without the need for a large solenoid coil.

Critical Point: A minimum of 1 psi pressure differential is required to allow the disc/piston/diaphragm to return to its normal position. Without this minimum pressure drop across the valve once in operation, the main port will not return to normal – this is THE key statement to remember.

Why Proper Sizing is Critical

There has always been a tendency in the industry to select solenoid valves based on line size – a practice that’s both risky and not recommended. This shortcut approach can lead to serious operational problems that affect the entire refrigeration cycle.

For example, if a liquid line solenoid valve is being selected for a system having a 5/8 inch OD liquid line, there’s often a tendency to simply select any valve having 5/8 ODF connections. However, we have 4 valve series with 5/8 OD connection sizes ranging from 6.0 tons to 23 tons – a massive capacity range!

Common Sizing Mistakes and Their Consequences

If a capacity of 15 tons is required, choosing solely based on line size can lead to two detrimental scenarios:

1. Under-sizing: Results in a starved evaporator, poor system performance, and potential compressor damage
2. Gross Over-sizing: The valve won’t have the minimum 1 psi pressure drop, causing its disc/piston/diaphragm to NOT return to its normal position

Proper Sizing Methodology

The correct approach is straightforward: Choose a solenoid valve based on system capacity with a minimum of 1 psi pressure drop. Then select from available connection sizes. If desired connection sizes are unavailable, bushings and couplings can be used to adapt without affecting valve performance.

Practical Example

Let’s walk through sizing a 15 ton, R410A liquid line solenoid valve with 5/8 OD connections:

Available Options:

1. E14 Series: Provides slightly over 3 psi pressure drop across the valve and has a 5/8 OD option
2. E19 Series: Provides slightly over 1 psi pressure drop across the valve, but only offers 7/8 OD option

For detailed specifications, refer to the Sporlan 30-10 bulletin: click here.

Integration with System Design

When incorporating solenoid valves into your system design, consider how they interact with other components. Just as proper heat load calculations ensure correct equipment sizing, proper solenoid valve selection ensures reliable system operation. This is particularly important in heat pump applications where reversing valves and solenoid valves must work in concert for proper seasonal changeover.

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Conclusion

Proper solenoid valve sizing is fundamental to reliable system operation. By understanding the difference between direct acting and pilot operated valves, respecting the minimum pressure drop requirements, and sizing based on capacity rather than line size, you’ll avoid common pitfalls that lead to callbacks and system failures.

Check out the link to my YouTube channel for more tips, tricks, and troubleshooting videos, and check out The HVAC Know It All podcast here or on your favorite podcast app.