Pump Seals: Most Common Styles

The spring is used to provide tension between the seal surfaces as they wear. It also provides tension on the seal when no product pressure is present. The two seals are machined using a process called lapping to achieve the necessary degree of surface flatness to achieve a leakproof operation.

As previously mentioned, mechanical seals are available in either single seal or double seal varieties. A single Mechanical Seal consists of a pair of sealing surfaces, while a double mechanical seal consists of two pairs.

Single mechanical seals are found in pumps used for simple duties such as pumping water, milk, animal fats, and beverages, as well as many other food processing applications. If the fluid to be pumped is more challenging in certain respects, then a double mechanical seal may be warranted to provide extra security. “Challenging” in this context includes fluids that are abrasive, such as crystalline sugar slurries.

Both single and double mechanical seals may also come with a flush. All types of mechanical seals generate heat from friction between the moving surfaces, and a cooling fluid — called a flush — circulates around the seal to remove the heat.

The flush provides constant lubrication when the product flow is not sufficient; the fluid flow is intermittent (e.g., entrained air in a CIP return pump); or the product is abrasive or sticky (sugar, chocolate, etc). This flush fluid may be the same as the fluid being pumped or an entirely different fluid and may be heated, filtered, or otherwise treated to improve its performance.

Double mechanical seals always come with a flush. Single mechanical seals can also be configured with a flush option (via a lip seal) without adding a second seal.

When you have a sugary or sticky liquid, the flush also helps remove particles that may be left behind in pumping certain products and helps to keep the seal wetted and safe from drying out. In the case of a manufacturer like Alfa Laval, a single mechanical seal with flush is available and solves most product sealing issues. Note: mechanical seals are more complex than O-rings, and require some care when installing.