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At some point in the life cycle of older pumps that still use gland packing seals to prevent, or, more accurately, limit process fluid leakage, you&#;ll look at the maintenance records and wonder if gland packing seals are still the best option. Would mechanical seals and seal support systems provide a better long-term solution? It&#;s really an exercise in weighing gland packing seal advantages and disadvantages on a pump by pump basis.
There are multiple factors to consider in making that decision. Based on many years of working with California Bay Area refineries, I&#;ve seen all the ways that they can be weighed&#;and the effects of those decisions. Reliability issues in light of limited budgets and increasingly demanding Cal/OSHA and BAAQMD regulations are always top-of-mind lately. With those priorities at the forefront, I think you&#;ll see that mechanical seals offer some significant benefits compared to gland packing seals.
Compare the Pros and Cons of Gland Packings vs Mechanical Seals
Of course, the weight you put on each of these comparison categories will vary according to your immediate and long-term budget, local HSE requirements, technical considerations, space constraints, and integration with existing equipment. However, I think you'll see that in most circumstances, the benefits of gland packing seals are on the decline&#;especially as mechanical seal technology improves.
Let&#;s take a look at several categories of comparison when deciding about gland packing seal advantages and disadvantages:
Purchase Cost
The initial costs of components and installation are a big lure for refineries to select gland packing seals, especially with many refinery budgets running on such thin margins right now. However, this is just one of the many considerations you should include in your cost/ benefit analysis.
Gland Packing Seal
Mechanical Seal
- Low cost of packing rings
- Depending on the pumping process, can be the most economic sealing solution
- Can be significantly higher cost, depending on the type of seal, accompanying seal support system, and any infrastructure retrofitting costs
Installation Process
From the perspective of time and cost, gland packings have the advantage&#;faster installation because of comparatively simpler design. The skills and experience of maintenance personnel play an important role in deciding the better option as well, though.
Gland Packing Seal
Mechanical Seal
- Quick installation
- No need to open pump housing
- Depending on the type of packing, there may be no need to decouple the driveshaft
- Can be installed by maintenance personnel
- Longer installation time
- Requires skilled maintenance engineers to properly install and align
- Pump housing must be opened and driveshaft decoupled
Durability
There&#;s no question that a mechanical seal&#;when properly maintained by a seal support system&#;wins the durability category. Reliability and process engineers need to justify the upgrade to a seal support system, though.
Gland Packing Seal
Mechanical Seal
- Varies greatly, depending on the tightness of gland packing, seal material, and seal lubrication
- Overtightening will result in rapid wear and loss of lubricity
- With a proper seal support system, mechanical seals should last a minimum of three years
- Monitoring of the seal support system and a preventative maintenance strategy can significantly extend mechanical seal life
Leakage
Depending on process conditions, loss of revenue-producing product, and safety or environmental concerns, the process engineer&#;s&#;and even the financial analyst&#;s&#;definition of acceptable leakage may be the factor that determines the gland packing vs. mechanical seal debate.
Gland Packing Seal
Mechanical Seal
- Ideal leakage is one drop per minute of process fluid per inch of outside shaft diameter. However, leakage can be as much as 10 times greater.
- Only in the event of
mechanical seal failure
- Dual seal arrangements offer the highest level of protection against leakage
Ongoing Maintenance
If you&#;re concerned about reducing maintenance costs associated with the frequency of inspections and replacements, then mechanical seals and seal support systems require a greater up-front investment but reduce maintenance demands in the long run.
Gland Packing Seal
Mechanical Seal
- Periodic tightening of the gland
- Eventual replacement of packing rings, determined by the quality and consistency of maintenance practices
- Monitor seal support system instrumentation to ensure proper seal chamber environment.
- For dual seals, add barrier/buffer fluid as needed to the seal pot
Energy Usage
There&#;s a clear, measurable advantage offered by mechanical seals: they are far more energy-efficient. If you have dozens to hundreds of pumps using gland packing seals, an upgrade to mechanical seals and seal support systems will deliver long-term energy savings, especially with high utility costs in California.
Gland Packing Seal
Mechanical Seal
- Friction between gland packing seal and impeller shaft can use up to six times more energy compared to a mechanical seal
- Results in minimum friction between seal faces and significantly greater energy efficiency compared to gland packing seals
Operational Costs
Energy and maintenance are the main factors here. Some mechanical seal support plans may have on-going supply costs that are canceled out by energy savings. In the long run, mechanical seals may pencil out to be the most cost-effective.
Gland Packing Seal
Mechanical Seal
- Higher energy costs
- Frequent tightening of the gland to minimize leakage
- Replacement of worn-out gland packings
- Lower energy costs
- Supply of seal support system flush, buffer/barrier, or quench fluids&#;water/glycol, hydraulic oil, or nitrogen
Environmental Risk
For refineries operating under Cal/OSHA or BAAQMD regulations, any leakage that brings environmental risks requires immediate attention. When environmental factors weigh heavily in your decision, mechanical seals and seal support systems offer peace of mind.
Gland Packing Seal
Mechanical Seal
- The leakage of wastewater or fugitive emissions can lead to fines or sanctions
- Mechanical seal designs and configurations of seal support system options offer the best choice for minimizing the risk of process fluid leakage that could lead to fines or sanctions
Two other factors to consider with regard to gland packing seal advantages and disadvantages: bearing damage and lost product due to leakage. Depending on their proximity to the driveshaft bearings, even minute leakage over time could contaminate motor and shaft bearings. The result is significant costs tied to unplanned downtime and bearing replacements. The cost of repetitive equipment failures can quickly negate the initial advantage of gland packing seals&#; lower installation and replacement costs.
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The other factor, leakage, is an inherent aspect of gland packing seals. In many instances, the leakage of process fluid, such as hydrocarbons, equates to lost revenue.
Replacing a gland packing seal with a mechanical seal can result in long-term savings that more than repay the cost of the mechanical seal and seal support system installation.
The Switch to Mechanical Seals
After you&#;ve applied the above criteria to your pumps and identified candidates where replacing gland packing seals disadvantages outweigh the advantages. In these cases, replacing them with mechanical seals and seal support systems makes sense. And you should seek the guidance of local mechanical seal and seal support stem vendors. Here&#;s why.
Mechanical seal vendors can advise you on the latest seal technology and variety of mechanical seal designs that best suit your specific processing needs. They&#;ll help you match the mechanical seal solution with the process fluid, temperature, pressure, and environmental conditions of each pump. This will eliminate the need for you to research the mechanical seal options and you&#;ll be assured of the best possible solutions for your specific needs.
Similarly, a local mechanical seal support vendor with substantial industry experience can advise you on the seal support system plans and configuration options available for each of the mechanical seals that are replacing gland packing seals. In comparison to mechanical seals, the range of seal support system options is far more complex. But an experienced mechanical seal vendor can explain why an API Plan 21 will provide longer seal life than API Plan 14, how good panel design and instrumentation reduce maintenance costs, or why API Plan 65B is the best solution to manage condensation of medium temperature fluids.
Swagelok has more than five decades of experience in helping petrochem refineries successfully make the transition from gland packing seals to mechanical seals and seal support systems. From initial on-site consultation and custom design of seal support systems to careful assembly and rigorous testing, Swagelok covers the full spectrum of mechanical seal support system services.
To learn how Swagelok Northern California can help you obtain the best performance from mechanical seals that have replaced gland packaging seals, contact our team today by calling 510-933-.
About Paul Lesnau | Sales Manager, Business Development Manager, and Field Engineer
Paul holds a B.S. in Mechanical Engineering from North Dakota State University. Before joining Swagelok Northern California, he was the West Coast Regional Sales Manager for an organization based in Illinois involved in pneumatic and hydraulic applications where he supervised product distribution throughout the western United States, Canada, and Mexico. While in this role, he was able to help provide technical and application-specific expertise to customers and distribution to drive specifications.
Overview of What Mechanical Seals Are
Mechanical seals are critical components used to prevent leakage in various types of equipment, primarily in pumps, compressors, and mixers. These seals are designed to maintain the integrity of a fluid system by ensuring that the fluid (liquid or gas) remains within the confines of the system and does not leak into the environment or mix with other fluids. The fundamental purpose of a mechanical seal is to create a barrier between the moving parts (typically a rotating shaft) and the stationary parts of the equipment, thereby preventing leakage and contamination.Mechanical seals are composed of several key elements: a rotating seal face attached to the shaft, a stationary seal face fixed to the housing, secondary sealing elements (such as O-rings), and a means of providing mechanical force (like springs) to maintain contact between the seal faces. The seal faces are usually made from materials with high wear resistance, such as silicon carbide or carbon, to endure the friction and pressure they encounter.
Different Types and Their Applications
Mechanical seals come in a variety of types, each designed to suit specific applications and operating conditions. Here are some common types of mechanical seals:
1. Pusher Seals
Pusher seals use springs or bellows to maintain contact between the seal faces. These seals are suitable for a wide range of pressures and temperatures. They are often used in general-purpose pumps and compressors.
2. Non-Pusher Seals (Bellows Seals)
Non-pusher seals utilize a flexible bellows assembly instead of springs to maintain seal face contact. These seals are ideal for applications involving high-temperature fluids or where seal face wear needs to be minimized. They are commonly found in chemical processing and petrochemical industries.
3. Cartridge Seals
Cartridge seals are pre-assembled units that simplify installation and reduce the risk of installation errors. These seals are used in applications where downtime needs to be minimized, such as in the food and beverage, pharmaceutical, and water treatment industries.
4. Gas-Lubricated Seals
Gas-lubricated seals use a thin film of gas (typically air or nitrogen) to maintain separation between the seal faces. These seals are suitable for high-speed applications and environments where liquid contamination must be avoided, such as in semiconductor manufacturing and aerospace.
5. Split Seals
Split seals are designed for ease of maintenance, allowing for seal replacement without disassembling the entire machine. These seals are often used in large pumps and mixers in industries like pulp and paper or wastewater treatment.
Benefits of Using Mechanical Seals Over Other Sealing Methods
Mechanical seals offer several advantages over traditional sealing methods such as packing (rope or braided seals). Here are the key benefits:
1. Leakage Prevention
Mechanical seals provide a much more reliable seal, significantly reducing the risk of leakage. This is crucial in applications involving hazardous or toxic fluids, where even minor leaks can pose significant safety and environmental risks.
2. Improved Efficiency
By minimizing leakage and reducing friction, mechanical seals enhance the overall efficiency of the equipment. This leads to lower energy consumption and improved performance.
3. Extended Equipment Life
Mechanical seals reduce wear and tear on the equipment by minimizing shaft damage and other issues associated with packing. This extends the life of the equipment, resulting in lower maintenance costs and downtime.
4. Reduced Maintenance
Mechanical seals require less frequent maintenance compared to traditional packing. Cartridge seals, in particular, simplify the installation and replacement process, further reducing maintenance time and costs.
5. Enhanced Safety
In industries dealing with volatile or dangerous fluids, mechanical seals are essential for maintaining a safe working environment. By preventing leaks, they protect workers and the environment from exposure to harmful substances.
6. Versatility
With a wide range of types available, mechanical seals can be tailored to suit various applications and operating conditions, making them a versatile solution for many industries.
Conclusion
Mechanical seals are indispensable components in modern industrial machinery, providing reliable and efficient sealing solutions across various applications. Their ability to prevent leakage, enhance equipment efficiency, and reduce maintenance costs makes them a preferred choice over traditional sealing methods. By understanding the basics and benefits of mechanical seals, industries can make informed decisions to optimize their operations and ensure safety and reliability in their processes.
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