The Siemens three-way set with motor drive SFA21 DN25T is commonly used in heating, sanitary and plumbing systems in residential and commercial buildings. It is typically installed in applications where precise flow control is required, such as in underfloor heating circuits, domestic hot water systems or zone control setups. The set is designed for use with two-position control signals and allows for manual override in case of power failure or system maintenance. The combination of a bronze body and a motorised actuator ensures reliable operation in a wide range of temperatures and flow conditions.

Installers working on central heating systems or building services will find this valve set suitable for integration into systems with a nominal pressure of PN16. The internal brass thread allows for secure and leak-free connections to standard piping systems. The valve is intended for use with water-based media and is compatible with control systems that provide a two-position signal. The actuator’s 10-second switching time ensures smooth and efficient operation, while the 1.8 m cable length provides flexibility in positioning the control unit.

Technical parameters

Stroke	2.5 mm
Weight	5 kg
Code	SXI46.25T/SFA21
Brand	SIEMENS

The stroke of 2.5 mm and Kvs value of 5.0 m³/h are critical for determining the flow capacity and control precision of the valve. These parameters influence the system’s ability to regulate flow accurately, especially in applications with variable load conditions. The leakage rate of 0 to 0.05% of the Kvs value ensures minimal flow loss when the valve is in the closed position, which is important for maintaining system efficiency and preventing unwanted .

Installation and connection

The three-way valve set is installed using the internal brass thread (1 inch nominal size). Installers should ensure that the piping system is compatible with the valve’s PN16 rating and that the media remains within the specified range of 1°C to 100°C. The actuator is connected via a 1.8 m cable, which should be routed carefully to avoid damage and interference. Common installation mistakes include incorrect orientation of the valve body or failure to align the actuator with the valve stem. A manual override function is available for emergency or maintenance situations, but it should not be used as a regular control method.

Compatibility and accessories

The SFA21 DN25T is compatible with control systems that provide a two-position signal and operate on 230V AC. It is typically used in conjunction with thermostatic controllers, building management systems or other automation devices. No additional accessories are required for basic operation, but installers should verify that the control system is correctly configured to match the valve’s switching time and signal requirements. No related products are available for this model.

Technical background for designers

The three-way valve operates by directing flow between two outlets, allowing for either mixing or diverting of media. The bronze body provides good resistance and mechanical strength, making it suitable for long-term use in water-based systems. The internal components are designed to withstand the specified temperature range and pressure conditions. The motorised actuator is integrated directly onto the valve body, reducing the need for external mounting brackets or supports. The system’s efficiency and service life are influenced by the quality of the installation, the media’s chemical composition and the regularity of maintenance checks.

Service and operation

The valve set requires minimal maintenance due to its robust construction and sealed actuator design. Regular visual inspections should be carried out to check for signs of wear, corrosion or leakage. The manual override function should be tested periodically to ensure it operates smoothly. No specific service intervals are provided in the technical data, but any issues with the actuator or valve body should be addressed promptly to prevent system downtime. The actuator’s electrical connections should be checked for tightness and insulation integrity.

Frequently asked questions

Can the actuator be connected to a 24V control system?
No, the actuator is designed for 230V AC power supply only. It cannot be used with 24V systems without additional conversion equipment.

Is the valve suitable for use with glycol-based media?
According to the manufacturer’s technical data sheet, the valve is suitable for use with water-based media. Glycol compatibility is not specified in the provided data.

Can the valve be used in a system with a pressure higher than PN16?
No, the valve is rated for a maximum pressure of PN16. Exceeding this pressure could result in damage to the valve body or internal components.

Can the actuator be replaced separately?
According to the manufacturer’s technical data sheet, the actuator is integrated with the valve body. Replacement of the actuator would require replacing the entire valve set.