Different applications for various mechanical seals

Oct. 18, 2019
Mechanical seals can solve a variety of sealing problems. Here are a few that highlight the versatility of mechanical seals and show why they’re relevant in today’s industrial sector. 
About the author: Megan Ray Nichols

Megan Ray Nichols is a STEM writer and blogger. More of her work can be found on SchooledByScience.com, and she can be reached at [email protected].

Mechanical seals can solve a variety of sealing problems. Here are a few that highlight the versatility of mechanical seals and show why they’re relevant in today’s industrial sector.

1. Dry Powder Ribbon Blenders

A couple of problems come into play when using dry powders. The main reason being that if you use a sealing device that requires a wet lubricant, it can result in the powder clogging around the sealing area. This clogging can be disastrous to the sealing process. The solution is to flush out the powder with either nitrogen or compressed air. This way, the powder won't come into play, and clogging shouldn't be an issue.

Whether you decide to use nitrogen or compressed air, make sure the airflow is clean and reliable. If the pressure reduces, then this could allow the powder to come in contact with the packing-shaft interface, which defeats the purpose of the airflow.

A new advancement in manufacturing covered in the January 2019 issue of Pumps & Systems  creates siliconized graphite materials using a chemical vapor reaction that converts the exposed areas of an electrographite to silicone carbide. The siliconized surfaces are more abrasion resistant than metallic surfaces, and this process allows making the material into complex configurations since the chemical reaction does not change the size.  

Installation Tips

To reduce dusting, use a discharge valve with a dust-tight cover to secure the gasket cap

Use lantern rings on the packing gland and maintain a small amount of air pressure during the blending process in order to prevent particles from accessing the stuffing box. This will also protect the shaft from wear.

2. Floating Backup Rings for High-Pressure Rotary Seals

Backup rings are generally used in combination with primary seals or O-rings to help the O-rings resist the effects of extrusion. A backup ring is ideal for using in high-pressure rotary systems, or in cases when significant extrusion gaps exist.

Due to the high pressure in the system, there’s the risk of the shaft becoming misaligned or the high pressure causing components to become deformed. However, using a floating backup ring in a high-pressure rotary system is an excellent solution because it follows lateral shaft motion, and the parts do not become deformed during use.

Installation Tips

One of the primary challenges associated with the mechanical seals in these high-pressure systems is to achieve the smallest possible extrusion gap clearance to minimize extrusion damage. The larger the extrusion gap, the more severe the damage to the seal could be over time.

Another necessity is to avoid metal-to-metal contact at the extrusion gap caused by deflection. Such contact could cause enough friction from heat to ultimately weaken the mechanical seal and make it less resistant to extrusion.

3. Double-Pressurized Seals on Latex

Historically, the most problematic part of a mechanical latex seal is that it solidifies when displayed to heat or friction. When a latex seal is exposed to heat, the water detaches from the other particles, which results in it drying out. When the sealing latex gets into the gap between the mechanical seal face, it is exposed to friction and shears. This leads to coagulation, which is detrimental to the sealing.

An easy fix is using a double-pressurized mechanical seal because a barrier fluid is created within. However, there's a chance that latex can still penetrate the seals because of pressure distortions. A sure-fire way to fix this problem is using a double cartridge seal with throttle to control the direction of the flushing.

Installation Tips

Make sure your pump is aligned properly. Shaft run out, deflection during a hard start, or pipe strains can throw off your alignment and will cause stress on the seal.

Always read the documentation accompanying your mechanical seals to ensure you install them the first time correctly; otherwise, coagulation can easily occur and ruin your process. It’s easier than some people expect to make minor mistakes that could interfere with the seal’s effectiveness and cause unintended consequences.

Controlling the fluid film that comes in contact with the seal face extends the life of the mechanical seal, and double pressurized seals give that control.

Always install your double-pressurized seal with an environmental control or support system to introduce the fluid barrier between the two seals. The liquid usually comes from a tank to lubricate the seals via a piping plan. Use level and pressure meters on the tank for safe operation and proper containment.

4. Specialized E-Axle Seals for Electric Vehicles

The e-axle on an electric vehicle performs the combined functions of the engine and the transmission. One of the challenges in sealing this system is that electric vehicle transmissions run up to eight times faster than the ones on gas-powered vehicles, and the speed is likely to increase even more as electric vehicles become more advanced.

The traditional seals used for e-axles have rotational limits of about 100 feet per second. That imitation means that electric vehicles can only travel short distances on single charges. However, a newly developed seal made from polytetrafluoroethylene (PTFE) successfully handled a 500-hour accelerated load cycle test that mimicked real-world driving conditions and achieved a rotational speed of 130 feet per second. The seals got put through 5,000 hours of endurance testing, too.

A close inspection of the seals after testing showed that there was no leakage or wear on the shaft or sealing lip. Moreover, the wear on the running surface was hardly noticeable.

Installation Tips

The seals mentioned here are still in the testing phase and not ready for widespread distribution. However, the direct coupling of the motor and the gearbox presents challenges related to the mechanical seals for all electric vehicles.

More specifically, the motor must remain dry while the gearbox stays lubricated. Those conditions make it crucial to find a dependable seal. Additionally, installers must aim to choose a seal that lets the e-axle travel at rotations exceeding 130 rotations per minute — the current industry preference — while reducing friction.

Mechanical Seals: Essential for Consistent Operations

The overview here shows that picking the right mechanical seal for the purpose directly influences the outcomes. Furthermore, getting familiar with the best practices for installation helps people avoid pitfalls.

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