The Scully Five Wire Optic Overfill Prevention System, Model SP-FU Series, is a safety device designed to prevent overfilling of tank vehicles and compartments carrying flammable and combustible liquids. It utilizes optic technology to detect the presence of liquid at a predetermined level, signaling for immediate shutdown of product flow to prevent spills and ensure safety.
Function Description:
The SP-FU sensor employs optic technology to detect liquid. When liquid reaches the sensor's sensing level, it triggers a signal indicating an impending overfill condition. This signal is transmitted to a Scully Socket mounted on the vehicle chassis. A plug and cable then connect these sensors to a Scully Overfill Prevention Controller located at the loading rack or fill stand. This system can be used as part of the Scully IntelliCheck® Overfill & Retained Product Monitoring System, as a stand-alone overfill prevention sensor with an appropriate Scully control monitor, or for "Scully Load Anywhere" applications.
The sensor is designed to be installed in a tank trailer compartment, typically positioned slightly above the compartment's normal fill capacity marker. Upon detection of liquid at this level, the sensor sends a signal to initiate an immediate shutdown of product flow, preventing spills and ensuring compliance with safety regulations.
Important Technical Specifications:
- Operating Temperature Range: -40°F to +140°F (-40°C to +60°C).
- Petroleum Product Range: Suitable for gasoline blends and light fuel oils.
- Exposed Materials: Constructed from aluminum, zinc, borosilicate (Pyrex®) glass, epoxy, conductive nylon, and Viton® seals, ensuring durability and compatibility with petroleum products.
- Detection Level and Size: The detection level is adjustable. Standard sensor shaft length is 7 inches, with longer shaft lengths (12 inches and 15 inches) and different holder cover heights (1 3/8 inches) available to accommodate various tank trailer mounting configurations and detection level requirements.
- Level Repeatability: 0.04 inches (±1 mm), ensuring precise and consistent liquid level detection.
- Electrical Leads: 18 inches (45 cm) long, 18 AWG (0.82mm²) wires for electrical connections.
- Cable Entry: Two holes, 1/2" NPT (M20 X 1.5) threads for conduit entry.
- Approvals: Intrinsically safe for mounting in Class I, Division 1, Groups C & D Hazardous locations, in accordance with Scully Control Unit approval ratings. FM and CENELEC approved.
Usage Features:
- Mounting Options: The SP-FU sensor is available with two main holder types for tank mounting:
- SP-FU/MHC (NPT Threaded Holder): This holder can be threaded directly into a 2-inch NPT opening (bushing) on the tank. This is the preferred method for secure installation and minimal maintenance. An Anti-Seize/Thread Lubricant (e.g., FEL-PRO® C5A® Copper Based Anti-Seize/Thread Lubricant) is recommended for vapor-tight joints and easy disassembly. Alternatively, it can be mounted through a 2 3/8-inch diameter hole using a gasket and conduit nut, though this method requires periodic checks for tightness.
- SP-FU/MHCF (Flanged Holder): This holder features a 6-bolt pattern conforming to the 2 1/2-inch TTMA flange standard, allowing direct mounting onto a man lid or tank shell. A gasket is installed between the holder and the tank, secured with six 1/4” hex head bolts, nuts, and lock-washers to ensure a vapor-tight seal.
- Sensing Level Adjustment: The sensor's sensing level, marked by an arrow on the prism protector, can be adjusted by loosening the extension shaft locking screw inside the sensor holder. The shaft can be slid up or down with a twisting motion to achieve the desired sensing height.
- Shaft Shortening: The sensor shaft can be shortened to a minimum of 5 1/2 inches (140mm) using a three-wheel tubing cutter. Care must be taken not to cut below the specified point and to file the edges to prevent damage to the O-ring. A wire protective cap should be inserted into the shaft to protect the sensor wires.
- Electrical Installation: All electrical connections between the sensor leads and vehicle wiring are made inside the sensor holder. Cable glands are used for strain relief and watertight installation. Unused holes must be plugged. The sensor has five wires: Black (ground/earth), Red (power), Green (diagnostic), Yellow (input signal), and Orange (output signal). Crimp connectors or other permanent means are recommended for connections, with non-conductive grease applied to prevent corrosion. Sufficient wiring length should be left as a service loop for maintenance. The label attached to one of the sensor wires must not be removed or cut off. Scully recommends using their special cable or 18 AWG (1mm²) or larger wires in conduit.
Maintenance Features:
- Sensor Replacement: Sensors are not repairable. A damaged or faulty sensor (shaft) must be replaced with an equivalent Scully sensor assembly. The replacement assembly includes a new O-ring for the holder. When replacing, the old O-ring should be carefully removed from the O-ring groove, and lubricant (petroleum jelly or white grease) should be applied to the new O-ring before installation to prevent damage.
- Periodic Checks: For through-hole mounting, the conduit nut should be periodically checked (at least yearly) for proper and continued tightness to maintain a vapor-tight seal.
- Cleaning: To avoid static charge, the sensor prism should only be cleaned with a damp cloth.
Safety Warnings:
- Always comply with NFPA-30, federal, state, local, and CENELEC regulations when working around the vessel.
- Do not smoke or perform metal work with product in the tank or when fuel vapor is present.
- Do not perform operations that may impair tank safety.
- Work on the vessel only when it is gas and vapor-free.
- Repair or replace leaking tanks before installation.
- Do not install or repair in hazardous areas to prevent ignition of flammable or combustible atmospheres. Maintain a distance of at least 6 feet from any fuel loading facility/operation during servicing/testing.
- Improper connections, component substitution, or tampering can impair intrinsic safety and create hazardous conditions. Regularly inspect sensor connections for wear or damage.
- Always wear safety goggles and protective clothing when working with potentially harmful or hazardous liquids.
- Do not install the sensor in aggressive substances that may attack the exposed materials.
- When setting the sensing level, account for ullage and emergency shutdown times to prevent spills from excess product flow.
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