|National offers a complete line of AST sensors designed to provide high level alarm contacts for above ground storage tanks. All units are fabricated in stainless steel and have a self-checking feature. It should be noted that the self-checking feature is magnetic, and thereby maintains the pressure tight function of the sensor, allowing these units to be installed in pressure vessels! There are three types of AST sensors, each engineered to satisfy the requirements unique to each tank design.
Mono-Check and Duo-Check: Single level and dual level AST sensors for cone roof or fixed roof tanks. They can provide high or high and high-high alarm points. Designed for use with intrinsically safe relays or other I.S. devices, they are built like our multi-level sensors, utilizing a single shaft for one or two levels. All have sealed contacts. These units are a perfect fit for tanks that utilize agitation or aeration with their product.
Versa-Level: Available in single or dual level format. These sensors are truly versatile. Engineered for service in internal floating roof tanks, they are part displacer, part float switch. The main benefit of these sensors is the ability to perform reliably in a tank with a stuck, or jammed floating roof. The displacer type heavy float is normally moved by the roof, causing the alarm contacts to be made; if the roof is jammed, the rising liquid in the tank will lift the float causing the alarm contacts to be made! Different cable lengths can be specified to accommodate alarm points. They may be used in cone of fixed roof tanks as well even though no floating roof is present. They are not a good choice if aeration or agitation is employed in the tank, nor should they be used in open/external floating roof tanks because wind and weather can cause false actuations with the biasing springs.
Adjustable Versa-Level: A variation which allows the end user to easily change the location of the float/s along the cable as needed in the field.
Versa-Level X: The AST sensor developed exclusively for external floating roof tanks. Because external floating roof tanks are open to the environment, they are subject to weather, leaves, debris, and in northern climates snow and freezing rain. The X models are pendant mounted, and actuate when the rising roof or product cause the sensor to topple or tilt into a horizontal position. Mounted individually or in pairs, they can provide High/High-High alarm contacts, and have operated very well under conditions that would cause other types of switches to malfunction. Variations of these units have been used in extremely viscous liquids such as asphalt.