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Seals: Mechanical Seals, Packing Seals and Lip Seals Why Use Them On Industrial Agitators?

When it comes to designing mixers Dynamix knows that environmental and process considerations are just as important as the mechanical mixer design. That is why our Solutions approach considers so much more than just the mixer application. We can configure your mixer to seal according to your process, environment, and pressure requirements.

Knowing which of these requirements is a priority and which technology is most cost effective is critical to your purchase. That is why Dynamix maintains its customized mixer design approach. You can define the seal you need as well as the manufacture, or we can help you make that decision.

  • Mechanical
  • Packing
  • Double Lip Seal
  • Cost / Performance

The  challenges for seals are as follows: To lower operating heat, lower seal and shaft wear, lower required power consumption, and lower parasitic friction. Brief descriptions of each type of seal are portrayed below. Our general options in agitator design are, lip seals, mechanical seals, and stuffing box seals (packing seals). 

LIP SEALS on Industrial Agitators:

In general the goal of a lip seal is to retain fluids or lighter pressures and keep the mixer operating at maximum efficiency. More commonly a lip seal also is a cost effective assurance that contaminants will not enter a mixing vessel. An effective lip seal must always be in contact with the rotating element; like the shaft of a mixer. The key to a lip seal’s success comes from proper material selection, installation, and maintenance. To prevent lip seal leakage, the initial installation is crucial, and following a proper maintenance schedule helps ensure its longevity.

PACKING SEALS on Industrial Agitators:

Packing seals are one of the oldest technologies. They stem back from the days when Miners would stuff their socks around shafts to reduce leakage. Today, the technology has evolved to a much safer and less fragrant materials. They are widely utilized for a vast majority of applications. In general, they are a rope-like material that wraps around the shafts of mixers within the gland to minimize fluid loss. Packing seals are a more economical choice than mechanical seals. By nature, packing seals have a continuous lubricant leak, between the shaft and packing material. Similar to a lip seal, choosing the right packing seal with proper packing material depends largely on the temperature, pressure, and other components of an application. Some industries utilize packing seals more than others. For example, many of our Heavy Industries still prefer them because they’re more forgiving.

MECHANICAL SEALS on Industrial Agitators:

Mechanical seals are utilized when seal pressure and vapor leakage cannot be tolerated. They have a higher initial cost, but the right one is the best option in the long term. Quality mechanical seals are the ideal match for Dynamix industrial agitators. Through customer requests or analysis, we can configure industrial agitators with mechanical seals from the leading mechanical seal manufacturers.

  1. Mechanical seals are more efficient than packing seals and stuffing box seals. I.E., packing seals consume more power to operate than mechanically sealed mixers.
  2. Mechanical seals reduce maintenance requirements. There is generally a large reduction in leakage and contamination possibilities compared to a packing seal.
  3. Mechanical seals reduce shaft or sleeve wear at the point where the shaft connects.
  4. Mechanical seals are often the best option for explosion-proof applications.

At Dynamix, we utilize more than a dozen different mixer seal designs. They can seal anywhere from vacuum tight to 25 Bar (362 psi) of operating pressure. Also, our seals can operate up to a 25 m/s (4921 ft/min) peripheral shaft speed. We fit our mixers with seals designed for pressures up to 20 Bar (290 psi) and peripheral speeds up to 20 m/s (4000ft/min).

With the correct construction materials, our mixer seals can cover the full pH range (0 – 14) of chemicals and can be supplied with FDA approved materials. With thousands of packing seal variations available globally, it may be difficult to assess their value and advantages in general. To keep it simple, we will focus on pressure and PH. Packing seals for mixers and agitators will seal up to 30 Bar (435 psi), with rotating speeds up to 25 m/s (4921 ft/min). Our seals will also cover the complete pH range, along with 3 FDA approved styles. Please keep in mind that packing seals generally have a leakage rate based on shaft diameter and pressure.

One new model is the Short Canister Mixer Seal (SCMS). An SCMS is our latest seal that is designed to meet today’s mixing requirements of faster, more efficient mixing in smaller vessels. The SCMS double seal is certified to ATEX zone 0 /20 for the 30 to 140 mm sizes. This is the equivalent of Class I Div. 1 (gases) and Class II Div. 1, (dusts), and Zone 1 / 21 & 2 / 22 for 30 to 220 mm sizes.

When mixing in closed vessels or tanks, pressure becomes a concern. The use of the right seal to deal with this pressure is important, as pressure by nature moves from high to low. If high pressure is a concern, lip seals are not a good option, as they tend to work better in a low-pressure mixing environment. A better option would be a stuffing box or packing seal. These seals can be used in high vessel pressure environments and obtained at a reasonable cost. Given that packing and stuffing box seals work use the fluid to keep the seal material lubricated, it may become a hazard in more toxic or volatile mixing environments. If volatile dust or vapors are present, a mechanical seal may be your best option.

Have a look at the table below regarding seals and pressure:




Mechanical seals are  more expensive option up front, but if the objective is lower maintenance costs and you have safety concerns regarding pressure, a mechanical seal is ideal. Not only does it work better in pressure mixing vessels, but it also works well at higher temperatures and higher RPM mixing environments. 

Given your specific application, a couple of configuration decisions may need to be made, as mechanical seals can be configured in various ways: Single vs. Double Mechanical Seals, and Solid vs. Split Mechanical Seals. Single Mechanical Seals are generally found in most mixer configurations at Dynamix. Double Mechanical seals are generally used in the Pump Industry, where the actual fluid touches the motor. A double mechanical seal provides a more security for reducing contamination. Of the two, Dynamix chooses to work with Single Mechanical seals. When deciding on whether to use Solid or Split Mechanical seals, it is generally a question of maintenance, accessibility, and cost. In simple terms, Split Mechanical Seals are usually more than double the price of Solid Mechanical seals. Split mechanical seals allow for easy maintenance of the seal without removing the motor. Although it is more expensive upfront, it saves downtime and maintenance costs when the mixer is put into production.

To reiterate, mechanical seals are not an inexpensive option up front. However, like Split mechanical seals, we recommend them for explosion proof situations, high risk product contamination situations, and ease of maintenance.

If you have process, environment, or pressure requirement which needs the right Seal, be sure to talk to one of our Applications Engineers at Dynamix.  We would be happy to walk you through the mixer, drive, mount, and seal configuration for your specific application.

Many of our customers ask for mechanical seals, as it gives them peace of mind for their explosion-proof characteristics. These seals are ideal in high pressure mixing and have lower maintenance requirements, but a higher capital cost up front.

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Split Mechanical Seal