GESTRA NRS 1-50 Water Level Switch is a high-performance steam boiler water level limiter from German valve brand GESTRA, part of Spirax Sarco Group. Designed for industrial boilers and hot water systems, the product works with NRG series electrodes to provide reliable water level monitoring and prevent low-water dry firing. It complies with the SIL 3 safety standard (IEC 61508), supports various boiler water conductivity conditions, and can be configured for one or two electrodes. As a genuine German-imported valve product, NRS 1-50 is recognized for reliability and durability in energy, chemical processing, and marine applications.

Product Functions and Features

• Low-water protection: When the water level falls below the minimum value set by the electrode, GESTRA NRS 1-50 Water Level Switch immediately triggers an alarm and, after a delay (standard 3 seconds, marine applications 15 seconds), opens the safety circuit and shuts down the heating system to prevent boiler damage.

• Automatic self-test and fault detection: The integrated self-test function continuously monitors electrode and connection status. If a fault is detected, such as a broken wire or interference, the system switches to a safe state and the LED indicates an alarm (green indicates normal operation; red indicates a fault).

• Multiple signal outputs: Equipped with 2 volt-free normally open contacts (6 A 250 V AC/30 V DC) and 2 semiconductor signal outputs (24 V DC, maximum 100 mA), supporting external alarm and interlock integration.

• Flush monitoring support: The standby input can be connected to SRL 6-50 logic unit to monitor the flushing process of connecting pipes (maximum bypass time 5 minutes), ensuring measurement accuracy.

• High safety level: The 1oo2 architecture provides Safety Integrity Level SIL 3, a service life of 20 years, and SFF >90%. The product complies with TRD and EN 12952/EN 12953 standards and carries UL 60730 and FM 7710 certifications.

• Flexible configuration: Code switches adjust the number of electrodes and support emergency single-electrode operation, which must be documented and repaired promptly.

For additional functional details, refer to the official document: GESTRA NRS 1-50 Datasheet (One-Electrode Version).

Technical Specifications

• Supply voltage: 24 V DC ±20% (0.3 A) or optional 100-240 V AC +10/-15% (47-63 Hz, 0.2 A).

• Power consumption: 7 VA/W.

• Response sensitivity: >0.5 ~ 10 ~ <10000 μS/cm (water conductivity at 25°C).

• Enclosure and protection: Polycarbonate enclosure, IP40 (terminals IP20), approximate weight 0.5 kg.

• Dimensions: 100 x 74 x 120 mm, suitable for installation on control cabinet DIN rail (TH 35).

• Environmental conditions: Operating temperature -10°C ~ 55°C, maximum relative humidity 95% (non-condensing), maximum altitude 2000 m.

• Connection requirements: Shielded multicore cable (minimum 0.5 mm²), maximum length 100 m (10 μS/cm sensitivity) or 30 m (0.5 μS/cm).

For complete specifications, download: GESTRA NRS 1-50 Datasheet (Two-Electrode Version).

Applications

GESTRA NRS 1-50 Water Level Switch is widely used for steam boiler water level control, hot water equipment protection, and marine systems. As a representative product from German valve brand GESTRA, it is suitable for:

• Steam boilers (EN 12952/EN 12953 standards).

• Pressurized hot water plants.

• Electric heating boilers and high-availability redundant systems.

• Marine applications (DNV/LR standards). Not suitable for potentially explosive atmospheres; electrodes require an additional barrier.

In industrial applications, NRS 1-50 helps ensure safe boiler operation, reduce downtime risk, and improve system efficiency.

Installation and Maintenance Guide

• Installation procedure: Secure the unit on TH 35 rail and use a safety power supply. When connecting electrodes, use shielded cable and ground it at the central earthing point (CEP) in the control cabinet. The external safety circuit must include an interlock function in accordance with EN 50156.

• Connecting pipe requirements: Steam pipe ≥40 mm and water pipe ≥100 mm. Internal installation does not require flush monitoring. External level vessels must be flushed regularly and equipped with a drain device.

• Maintenance notes: Check switching points annually and use the test button to simulate an alarm. Allow 24 hours for thawing after transport. Avoid high-frequency interference by using an RC network and ferrite rings.

• Safety instructions: Installation must be performed by qualified personnel. Terminals remain live during operation; disconnect power before servicing. External fuse: 0.5 A (semi-time-lag).

Download the installation manual: GESTRA NRS 1-50 Installation Guide (Two-Electrode Version).