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High Level Shut Off for Filler Arm Loading

High Level Shut Off for Filler Arm Loading
Tank trucks and railroad tank cars carry more than 95% of all liquids and solids transported overland. Products include everything from hydrocarbons and chemicals to food and dairy.

Tank trucks and cars are filled at filling depots. These depots may be part of the production plant or may be storage facilities at marine and railroad depots. Many of these facilities will have filler arms that are positioned over the tanker for filling.

Filler arms in all cases should have a high level shut off switch to indicate when the tanker is full. An overfill can result in loss of product, clean up, potentially hazardous conditions, and EPA spill reporting.

Filler arms are punishing locations for point level instruments. The high level sensor used in these applications is subject to heavy impacts and vibration and exposed to extreme conditions. The products being transported are often sticky and coat heavily. These installations require robust, industrial instruments that can stand up to the severe environment.

Many facilities will underestimate the demands of this application and will install a low priced float or vibrating switch. These technologies will not last long in this environment. It’s important to understand that the prevention of one spill and the associated loss of material, clean up, and fines will pay for a quality level switch many times over.

Level Measurement Technologies
The following is an assessment of the most common point level technologies used for filler arm shut off.

Floats have been used for filler arm cut off but are problematic in this application. The float can jam or hang up preventing the switch to alarm in a high level condition. The float guide arm or tether can easily be damaged while moving the filler arm and the float can be punctured causing it to sink. Also, there is no conclusive way to test the functional integrity of a float without actually using it in the product being transported. 

Tuning Forks and Vibrating Rods
A filler arm is the last place a tuning fork or vibrating rod should be used. Damage to the sensor from impact will cause the resonating frequency to shift resulting in false alarms or total switch failure. This is true of both tuning forks and rod type vibrating switches. With filler arm installations senor damage due to impact is not a question of if but of when.

Ultrasonic Gap Switches
Gap switch sensors such as the VeriGAP product by Drexelbrook are fully potted which protects the crystals from damage due to light to moderate impacts. The electronic unit can be remotely mounted allowing only the sensor to be located on the filler arm. The VeriGAP is available with both manual function check and a Self-check option that ensures the operational integrity of the switch at all times.

Gap switches are suitable for measuring clean, non-coating liquids and are applicable to filler arm installations where these products are being transported.

RF Admittance - The Best Choice!
Drexelbrook RF Admittance switches such as ThePoint and the Intellipoint are the best solutions for filler arm high level cut off. The sensing elements are made of a solid steel rod and have no moving parts making them the logical choice for this type of installation.

Sensing elements are available with diameters up to one inch for the most punishing installations. Materials are available that are chemically compatible with any material being transported. RF Admittance driven shield circuitry ignores even heavy coatings on the sensing element eliminating false high level alarms. Electronic units can be remotely mounted leaving only the sensing element in the abusive environment.

The Intellipoint has a self-check feature that continuously monitors the functional integrity of the switch and indicates a fault if it is not operating properly.

Robust RF Admittance sensors are undoubtedly the best solution for the challenging filler arm installations.

• No Moving Parts
• Solid Rod Sensing Elements
• Cote Shield Eliminates false trips
• Remote mounting puts the electronics in a safe location