Danfoss Introduces Fast-Acting Staging Valves

In centrifugal chillers and heat pumps—used in sectors such as data centers, hospitals and industrial cooling—surge prevention and controlled pressurization during startup are essential for protecting compressors and maintaining overall system efficiency. Danfoss has introduced its PTS staging valves as part of the EXO – Extended Oil-Free program to address these operational challenges in both oil and oil-free systems.

Fast Valve Response to Prevent Compressor Surge
Compressor surge typically occurs when the pressure ratio falls below stable operating limits, especially during startup. The PTS staging valves are engineered to respond within 5 seconds, which is fast enough to counteract rapid pressure drops that can otherwise lead to reverse flow, vibration and internal shock. By opening quickly to connect the discharge line to the suction side via the evaporator, the valves help build pressure before the discharge check valve opens. This stabilizes the compressor’s operating conditions and reduces the risk of surge-related damage.

The rapid response also shortens the overall startup sequence, allowing the compressor to reach steady-state operation more efficiently. When needed, the same valve can function as a load-balancing valve to help maintain stable flow and pressure during transitions.

Pressure Relief and Component Protection During Shutdown
During normal shutdown, the staging valve opens as the compressor slows, allowing pressure to be released in a controlled way. This reduces the likelihood of shaft-bearing contact and excessive mechanical stress on internal components. Because the valves are sized to accommodate demanding compressor pressure ratios, they provide stable shutdown performance even under high differential pressures.

In abnormal conditions, such as faults or power loss, the discharge valve closes while the PTS staging valve opens immediately to relieve trapped pressure and protect critical compressor components.

Design Characteristics and System Integration
The PTS valves are built using corrosion-resistant materials that support long service life in oil-free environments, where lubrication cannot compensate for material wear. Refrigerant compatibility includes all major refrigerants, including A2L types, increasing their applicability in modern low-GWP system designs.

The valves are available in multiple sizes with Kv values between 18 and 38, allowing OEMs to match valve capacity to chiller or heat-pump system requirements without oversizing. Their 5-second actuation time is achieved through a controlled opening profile that promotes tight sealing and stable pressure regulation. Integration is simplified through compatibility with Danfoss drivers such as EKF, EKE 100 and Alsmart^® controls, enabling coordinated motion control without custom interface development.

Performance with Turbocor^® Compressors
Optimized specifically for Danfoss TGx and TTx Turbocor^® compressors, the PTS valves support high pressure-ratio operation, contributing to smoother transient behavior and improved system reliability. When paired with these compressors, the valves help maintain pressure balance during rapid load changes—an important factor in achieving energy-efficient operation in oil-free centrifugal systems.

Comparison with Traditional Valve Technologies
Conventional solenoid valves or standard stepper motor valves often require multiple units to achieve the same flow capacity provided by a single PTS valve. The higher Kv values of the PTS range allow large bypass flows without introducing excessive pressure drop. The valve’s sealing design also improves tightness under high pressure, reducing the risk of internal leaks and associated efficiency losses.

The controlled bypass path reduces pressure spikes by ensuring that recirculation through the evaporator happens in a predictable way. This contributes to reduced mechanical stress and helps maintain stable compressor operation during both transient and steady-state conditions.

Options for OEM Chillers and Heat Pumps
Manufacturers can select from three PTS valve models covering Kv values from 18 to 38, supporting a wide range of system capacities. The PTS product line integrates with Danfoss’s broader component portfolio—including ETS expansion valves, controllers and oil-free ball valves—allowing OEMs to design complete oil-free systems with consistent performance characteristics across liquid, suction and discharge lines.

www.danfoss.com