Picking Your Mechanical Seal

Seals are vital to the functionality of any pump - but how do you pick a seal? The first question is whether you want an internal or an external seal. Internal seals sit inside the pump head with the product. External seals sit behind the pump head and are kept mostly dry and separate from the product. Once you have picked a seal location you can pick your seal type. When choosing your seal you should be considering the product being pumped, the temperatures, and the general pump needs.

Mechanical Seals

While there are many seal options including the packing seal, and o-ring seal, the majority of sanitary pumps use mechanical seals. Mechanical seals are first and foremost sanitary, but they are also durable and easily replaceable. They use pressure to create a seal between the two seal faces with a thin layer of liquid between them for lubrication and use secondary seals to help prevent leaks around the faces.

Mechanical seals often feature:

• Primary rotating seal face on the shaft
• Primary stationary seal face on the housing
• Secondary seal on the rotating seal and shaft
• Secondary seal on the stationary seal and housing
• A method to maintain pressure on the seal faces when the pump is not running
• A mechanism to keep the stationary seal faces, stationary (duh)
• A method of fixing and maintaining the working length of the seal

The primary seals protect the housing or backplate and the shaft from wear. It  is comprised of two pieces: a stationary and a rotating seal. The stationary seal is located on the housing or backplate and the rotating seal is located on the shaft. Both primary seals have a extremely smooth faces to prevent undue friction. When the pump is running the pressure of the liquid presses the two seal faces together. When the pump is not running, a secondary pressure source is required to keep the faces together, this is often a spring, a series of springs, or occasionally a large squishy o-ring. A secondary seal is used between the rotating primary seal and the shaft, and between the stationary seal and the housing. The secondary seals prevent leakage from occurring; it can be a gasket, wedge, cup, or an o-ring seal. Minor leakage between the two primary seals is necessary to lubricate the seals and allow them to continue moving smoothly. The heat and movement of the pump and seal causes the liquid from the leak to evaporate quickly.

Our Mechanical Seals

There are many different ways to make a mechanical seal. Not all mechanical seals are made equal. Our C-series pumps use a polished stainless steel backplate that serves as the stationary seal face. The backplate does not require a secondary seal, because it cannot leak. A ceramic or silicone carbide seat can be added if wanted, to protect the backplate from damage.

Our Hyginox internally sealed pumps and our RF pumps both have a silicone carbide or ceramic seat for the stationary seal face; the seats are pressed in to prevent their movement. The RF pumps and the Hyginox series pumps use an u-cup seal as a secondary stationary seal.

As a secondary seal on the rotating seal face of the C-series pumps we use an o-ring. The RF and Hyginox pumps use a bellows seal. We use one large spring in all of our pumps to serve as the pressure on the primary seals. A drive collar is used on C-series pumps to maintain and fix the working length while the RF pumps use a step in the shaft. Because the Hyginox pumps have an internal seal the impeller serves this function.

External Seals

External seals are easy to install, clean, check and maintain. They are ideal for corrosive materials, because the seal is separate from the product being pumped and will not be affected by corrosion. Because they are external, if the seal does malfunction and a piece comes loose, then it is separate from the product and will not harm anything. External seals have add on options of a seat (DG Seal) or a water cascade (F seal).

D Seal

The CPE D seal is a single mechanical external seal. This is a traditional external mechanical seal. You cannot run the pump dry with this seal. It is recommended for liquids that will not crystalize or solidify.  This seal is often used in the brewing and alcohol, and beverage industries.

DG Seal

The CPE DG is a single mechanical external seal with a ceramic seat. It functions in the same way as a D seal, however there is an addition of a ceramic seat and flat teflon gaskets that protects the back plate from damage. The seat sits between the rotating seal and the back plate. When damage occurs, it is easier to replace a seat than the entire backplate. The DG seal is recommended for more abrasive products that may damage the back plate.

F Seal

The CPE F seal is a single mechanical external seal with a water cascade. This is also known as a flush seal. Water needs to be hooked up to the pump and provides the cascade on the pump seal. The water keeps the seal clean, cool, and lubricated. This can help with the longevity and durability of the seal. An F seal is recommended for products that may crystalize, coagulate, or solidify, because the seal is continuously cleaned. Products that are high in sugar, or are sticky and viscous can leave a powder or residue on the seal, the water cascade washes it off.

Internal Seals

Internal seals are ideal for viscous or hot products. The majority of the rotating portion of the seal is inside of the pump head with the product. Internal seals are constantly lubricated and flushed clean by the product being pumped, and are cleaned by the CIP process because of their handy location. The product serves to keep the seal cool and functioning correctly. Internally sealed pumps are becoming increasing popular in the brewing and craft beverage industry because of the high sugar content of the product being pumped. Our CB+ and Hyginox series pumps are a centrifugal pump that features an internal seal.

Picking a seal can be stressful and confusing. The product, speed, and pump requirements should all be considered when picking the perfect seal for your pump.