Dust and Vapor Seals

Dust seals and vapor seals are used primarily when the main objective is to reduce the possibility of product contamination from external sources, such as dust or rain water. Vapor seals can also be used to reduce evaporation from the tank, or to reduce the odor of a foul smelling product escaping from the tank. The most typical styles of dust and vapor seals are as follows:

• DUST CUPS are essentially an inverted plastic cup mounted on the shaft with an 0-ring. The cup is designed to slip down over a small nozzle on the tank roof which the shaft passes through, acting like an umbrella to divert water and debris from entering the tank. Dust cups are not designed to hold any pressure, in fact vapors can pass around the space between the cup and the nozzle.

• EXCLUDER SEALS are a type of lip seal, but rotate with the shaft. The body of the excluder is usually split and held onto the shaft with a spring or "zip strip". A skirt extends downward and rides directly on the tank roof, creating a simple seal.  Excluder seals are available in rubber and viton.

• SPLIT RUBBER DUST SEALS are comprised of two sheets of 1/4" thick rubber bolted to the tank roof which cover the hole where the mixer shaft enters the tank. Each sheet is split and has a tight clearance hole in the center which rides on the shaft. The splits are staggered to minimize leakage.

• VAPOR LIP SEALS normally consist of two lip seals mounted back to back and ride on the shaft to create a seal. The seals are usually mounted in a flange made of mild steel, mild steel faced with stainless or UHMWPE. The flange can be attached to the mixer drive and perform as a mounting base for the mixer, or remote mounted on the tank roof below the mixer drive. When attached to the drive, vapor seal flanges are registered to guarantee concentricity. If remote mounted, it is critical to adjust the flange so that it is centered around the shaft, or the flange may wear on the shaft and cause damage.