Multi Position Valves and More - Short #293 · HVAC School - For Techs, By Techs summary

Key takeaways

Multiy-position service valves provide full bore flow and are essential in commercial systems for efficient service and recovery operations.
Always loosen the packing nut before turning the valve stem to avoid damaging the packing material or snapping the stem.
Keep multi-position valves mid-seated during brazing to prevent surfaces from warping and to avoid damage from heat.
Never operate the suction or discharge valves while the compressor is running in a front-seated position; doing so can cause severe damage or system failure.
Properly identifying and operating king and queen valves is critical for safe, effective pump-down and service procedures.
Understanding the internal mechanism and correct positioning of these valves is key to preventing costly mistakes and system damage.

Summary

Introduction to Service Valves and the Episode Focus

The episode starts with Bryan introducing the topic of multi-position service valves, a critical component especially when transitioning from residential split systems to larger commercial or industrial systems. The episode aims to clarify the operation of various types of service valves, including traditional Schrader valves, CoreMax, and multi-position valves, highlighting their advantages, limitations, and proper handling techniques.

Overview of Common Residential Service Valves and Limitations

Bryan reviews typical residential HVAC service valves, emphasizing their design featuring brass bodies, hex caps, and Schrader ports. These valves are simple: the valve is accessed via the Schrader core, which is spring-loaded and restrictive, making the process of pressure measurement and refrigerant charging straightforward but restrictive and prone to leaks. He notes these valves are suitable for everyday service but not ideal for systems requiring full port access or frequent operations.

Discussion of CoreMax Valves and Their Pros and Cons

The episode compares CoreMax valves, which resemble a larger Schrader, offering higher flow rates and ease of use with core depressors. However, they come with drawbacks, notably difficulty replacing internal cores and the risk of internal steel failure, which can complicate service operations. Bryan advises caution when using CoreMax valves to avoid damage and misoperation.

Multi-Position Service Valves in Commercial Systems

Bryan explains that large commercial systems often use multi-position service valves, which lack spring-loaded cores and are operated manually with wrenches. These valves feature a solid stem that can be turned to different positions—backseated, cracked off, or front-seated—each serving a specific purpose, such as normal operation, pressure measurement, or isolation. He emphasizes the importance of correct operation, such as loosening the packing nut before turning the stem to prevent damage.

Handling and Operation of Multi-Position Service Valves

Bryan details the correct procedures for operating these valves, including loosening the packing nut to prevent damage during stem rotation, and the importance of keeping the valve mid-seated during brazing to avoid warping. He describes the three main positions: - Backseated: Full flow, no access to service port, system running. - Cracked off: Slight opening for pressure readings. - Front-seated: System isolated, used for repairs, but dangerous if used while running as it can damage compressors.

Risks of Improper Valve Operation in Compressors

The episode covers the serious consequences of improperly using these valves, especially on compressor suction and discharge lines. Front-seating the suction valve while running causes loss of motor cooling and risks electrical arcing, potentially destroying the compressor. Similarly, front-seating the discharge valve while running can cause catastrophic internal damage. Bryan stresses understanding these risks and proper procedures for system safety.

Difference Between King and Queen Valves and Their Uses

Bryan describes king valves, located at the outlet of the receiver for pump-down procedures, which are fully front-seated to trap refrigerant on the high side. Queen valves are similarly designed but located at the inlet of the receiver, mainly used in large systems to isolate the receiver. Proper operation of these valves allows safe service and recovery procedures.

Summary and Additional Tips

The episode concludes with practical tips for handling these valves, such as maintaining clean and cool brazing environments, understanding the internal flow path, and correctly identifying each valve's purpose. Bryan also hints at future visual aids to better illustrate these concepts.

Show notes

In this short podcast episode, Bryan talks about multi-position service valves and more valve types.

Many typical residential systems have brass service valves with a hex cap and Schrader ports; access happens solely through the Schrader ports (where the cores are). Schraders are restrictive and prone to leaking, and they don't have the ability to back-seat or front-seat. In applications where we need that capability, we use multi-position service valves instead. (Note: CoreMax valves have much higher flow rates, but you can't remove the cores except with a highly specialized tool.)

Multi-position service valves are common in commercial refrigeration and allow for unrestricted, full-port flow. They do not have spring-loaded cores in the service port. If you treat these valves like Schrader valves, refrigerant WILL come out if it's not back-seated. You adjust the position by turning the stem with a refrigeration service wrench; loosen the packing nut before attempting to turn the stem, as tightening it down will crush the compressible packing material around the rotating stem. Tighten it back down after making your adjustment.

These valves also require lots of heat to braze, so we must cover heat-sensitive surfaces with wet rags or heat-blocking putty (like WetRag by Refrigeration Technologies). The valve must be mid-seated while brazing, not fully front-seated or back-seated, as the surfaces are more likely to warp otherwise. Mid-seating the valve also provides a high-volume path directly to the system. Back-seating the valve is the everyday running position (stem must be rotated fully counterclockwise) and blocks access to the service port. Cracking off the back seat requires you to rotate the stem slightly clockwise with service hoses securely attached, just enough to allow you to get a reading through a tiny gap. Front-seating the valve is good for isolation with the compressor off but may cause compressor failure or serious injuries if you run the compressor. Front-seating requires you to rotate the stem fully clockwise; it completely blocks the flow of refrigerant through the system, and the service port stays open to the upstream side of the valve body. Catastrophic compressor failure will happen if the suction or discharge valves are front-seated while running.

General multi-position service valves are NOT king valves. King valves are multi-position service valves specifically located at the outlet of the liquid receiver. These valves front-seat to help you pump down the system when you need to do repairs on the low side; it blocks liquid refrigerant from leaving the tank. A queen valve may be located at the inlet of the receiver on the drop leg from the condenser; front-seating it with the king valve will fully isolate the receiver.

Multi-position service valve tech tip: https://www.hvacrschool.com/compressor-multi-position-service-valves/

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Multi Position Valves and More - Short #293