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118127 – Gems Sensors LS-77700 Series Bent Stem Level Switch
Available now on the Airparts.aero Marketplace.
The Gems Sensors 118127 is a precision-engineered, single-point liquid level switch belonging to the high-reliability LS-77700 series. Designed with a unique bent-stem configuration, the 118127 is specifically tailored for side-mount installations where a vertical drop is required for the float to actuate. This design provides superior buoyancy and performance in liquids with a low specific gravity (as low as 0.45), making it an ideal choice for monitoring fuel levels, lubricating oils, and hydraulic fluids in both industrial and aerospace ground support applications.
Constructed with a robust brass stem and a high-buoyancy Buna N float, the 118127 is engineered to withstand operating pressures up to 300 PSI and temperatures reaching 300°F. The switch utilizes a reed-switch mechanism that is hermetically sealed within the stem, ensuring the electrical contacts are isolated from the process fluid. This "dry-contact" design ensures long-term reliability and eliminates the risk of spark ignition in volatile fluid environments, provided it is used within its rated electrical limits.
Key Features
Bent-Stem Geometry: Optimized for side-wall mounting while allowing the float to move vertically, providing a small footprint inside the tank (less than 3 inches of protrusion).
Low Specific Gravity Capability: The high-volume Buna N float allows the switch to operate reliably in light oils and hydrocarbon fuels with a specific gravity as low as 0.45.
Hermetically Sealed Reed Switch: The SPST (Single Pole Single Throw) switch is protected from environmental and fluid contamination, ensuring millions of cycles of trouble-free operation.
High-Pressure/Temperature Resilience: Rated for 300 PSI and a temperature range of -40°F to +300°F, suitable for demanding hydraulic and engine oil monitoring.
Durable Brass Construction: The 3/8"-24 UNF threaded stem is machined from high-quality brass for superior corrosion resistance and mechanical strength.
Technical Specifications
Part Number: 118127
Manufacturer: Gems Sensors & Controls
Series: LS-77700
Switch Type: SPST (20 VA)
Switch Operation: Normally Open (Non-Reversible)
Mounting Size: 3/8"-24 UNF-2A (Horizontal Mount)
Stem Material: Brass
Float Material: Buna N
Wetted Materials: Brass, Buna N, Beryllium Copper
Max Pressure: 300 PSI
Temperature Range: -40°F to +300°F (-40°C to +149°C)
Min Liquid SG: 0.45
Electrical Termination: 24" Long, 22 AWG, Polymeric or Teflon-jacketed leads
Aircraft & Support Compatibility
Ground Support Equipment (GSE): Ideal for level sensing in hydraulic power units (HPU), fuel bowsers, and aircraft tug oil reservoirs.
Auxiliary Systems: Used in specialized environmental control units and non-flight-critical secondary fluid tanks.
Industrial Powerplants: Suitable for stationary generators and turbine oil sumps.
Note: For flight-certified applications, refer to the aircraft’s Illustrated Parts Catalog (IPC) to verify the correct TSO-certified equivalent.
Applications
The 118127 is utilized for Point-Level Fluid Detection. Its primary roles include:
Low Fuel/Oil Alarm: Providing an electrical signal to trigger an alarm or shut down a pump when fluid levels drop below a critical threshold.
High-Level Cut-off: Preventing tank overfill in small-volume sumps or specialty chemical tanks.
Leak Detection: Monitoring "dry" sumps or secondary containment areas for the presence of leaked hydraulic fluid.
Why Choose 118127?
The Gems Sensors 118127 is the industry standard for high-buoyancy side-mounting. Unlike standard vertical float switches, the bent stem allows for installation in shallow tanks or areas with limited vertical clearance. Choosing a genuine Gems switch ensures that the internal reed switch is calibrated to the exact magnetic flux of the float, preventing "nuisance tripping" or failure to actuate in low-density fluids.
The 118127 operates via Magnetic Reed-Switch Actuation. The internal mechanism consists of a reed switch—two overlapping, ferromagnetic metal blades—sealed in a glass tube. As the Buna N float (containing an internal permanent magnet) rises or falls along the stem, the magnetic field interacts with the reed blades. When the float reaches the actuation level (typically 2-3/8 inches from the mount), the magnetic force overcomes the mechanical stiffness of the blades, closing the circuit (Normally Open). Because the 118127 uses a bent stem, it leverages a larger float volume than traditional side-mount switches, ensuring that even in non-Newtonian fluids or low-viscosity hydrocarbons, the buoyancy force is sufficient to overcome internal friction. This is critical for preventing "switch hang" in cold-weather oil applications where viscosity is high.
Note: This is a sensitive electrical sensor. Do not subject the switch to loads exceeding 20 VA, as this will weld the reed contacts together; use an isolation relay for high-current loads. Ensure the 3/8"-24 threads are properly sealed with a fuel-resistant compound. Installation must be performed by a qualified technician. Periodically check the float for "water-logging" or debris accumulation that could affect buoyancy.
