Mechanical Seals

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Our Mechanical Seals

Here at Totally Seals® we offer a vast range of mechanical seals for all pump types and industries. We are proud to distribute Vulcan Seals high quality and UK supplied products with same day dispatch (before 2pm) and next day delivery.

If you would like to discuss your seal requirement please get in touch via email or you can give us a call on 02921 251 998.

If you have an emergency we can offer fast quotations - whilst we are not open 24 hours if you mark your email as urgent we will endeavour to deal with your requirement early on the next working day.

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Totally Seals® Mechanical Seal Guide 

How do they work?

A mechanical seal can be used to create a sealing face in any system where rotating shaft protrudes from or into a housing. The vessel may be filled with fluids or be under pressure but the seal must maintain the rotating action and be reliable. Gland packing was traditionally used for this purpose but in higher specification machinery a mechanical seal is necessary.

In a regular mechanical seal, there are three basic mechanisms working to maintain the seal:

 

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There are slight variations to this but this is the general principle to which all mechanical seals work. 

Mechanical Seal Types

Rubber Diaphragm

Rubber diaphragm mechanical seal totally seals vulcan

The drawing above shows the standard section of a rubber diaphragm seal. The shaft seal is provided by the rubber diaphragm which is squeezed onto the shaft by the drive ring. Once fitted, the rubber diaphragm will grip the shaft giving a strong static seal and very positive drive, via the drive ring, to the seal face.

As there is no relative movement between the shaft and the rubber diaphragm, shaft fretting, wear and hang-up hysteresis are eliminated and the seal can immediately accommodate some shaft run-out and misalignment.

Shaft axial movement and the movement required during the working life of the seal is handled by the elastomer rubber flexing at it’s junction point (Red Area on diagram). The seal head automatically adjusts to compensate for any face misalignment, usually caused by shaft end float / pump body misalignment.

The closing spring force and the seal pumping pressure force maintain the faces in full contact, whilst the rubber diaphragm acts as an elastomeric bellows providing sustained flexibility. Positive drive of the seal face is transmitted via the drive ring and retaining housing and not via the spring, which merely provides some closing force to the mechanical seal faces. These seals can therefore be used to seal shafts rotating in either direction and in vacuum applications.

If you need any help or advice, please don't hesitate to get in touch.

Rubber Bellows

rubber elastomeric bellows mechanical seal totally seals

Rubber (elastomeric) bellows seals are of compact design with a sealing action that provides many benefits. The bellow’s high strength and flexibility is the key to the very reliable performance of this type of seal; as it readily accommodates seal misalignment, end-float and seal face wear.

The convoluted bellows profile makes these seals ideal for media prone to clogging or for hygienic applications. Designed for confined spaces and limited gland depths.

O-Ring Mounted

oring mounted pusher type mechanical seal totally seals pump

‘O’-Ring mounted mechanical seals have a small cross-section and a complete recessed ‘O’-Ring housing. A narrow seal head width allows the seals to easily fit confined DIN 24960 (EN12756) housings, whilst also providing the benefits of reduced face surface running speed, with increased circulation around the seal faces.

Seal loading is provided by conical springs or wave springs, with conical springs being the most common. Seal drive is provided by the conical spring tightly gripping the shaft at it’s base, or by grub-screws in the case of wave-spring seals. Conical Spring seals are supplied as standard with right-hand drive springs for clockwise shafts. Left-hand springs for anticlockwise shaft rotation should be specified on order.

Utilisation of wave spring technology in the seals allows the design of extremely compact seals, in both the axial and radial directions. Wave springs provide equal loading and deflection at a fraction of the free height when compared to helical springs, making them suitable for limited spaces.

Other main advantages for mechanical seal use are their insensitivity to contaminates, whilst providing straightforward fitting. These main characteristics make wave springs ideal for food, chemical and restricted fitting applications which are prone to clogging. Our resilient ‘O’-Ring mounted seal designs are technically efficient (readily accommodating misalignment and vibration) and are highly versatile.

We offer a wide range of face material combinations and spring / seat sizes to suit most applications. Our design standard of a narrow cross-section head with full recessed ‘O’-Ring groove, combined with alternative seal face materials, maximises seal performance and prolongs seal life.

PTFE Wedge

PTFE Wedge Mechanical Seal pump  type totally seals

The chemically resistant P.T.F.E. component is spring loaded, to force the flexible angular lip of the wedge, into tight contact with the shaft. The same spring force impacts a sufficient load to the rotary face to create a suitable seal interface, with a varied choice of standard stationary seats.

The features associated with the wedge seal design make these seals ideally suited for chemical process pumps and many other aggressive media applications.

Other Variations

In addition to the four primary types of mechanical seals it should be noted that some have sub-types that enable to seal to perform under differing environments such as pressure, temperature or the type of media that is being pumped.

Some mechanical seal variants can go by different names to the ones listed above. There can often be some overlap in how various manufacturers might name them so please be aware of possible confusion. But if you are not sure please feel free to ask

These additional variations can be:

Balanced or Unbalanced types

The balance of a seal refers to the distribution of load across the seal faces. If there is too much load on the seal faces, it can lead to a leakage of fluids from within the seal which essentially renders the seal useless. Moreover, the liquid film in between the seal rings runs the risk of vaporising. This can result in higher wear and tear of the seal, shortening its life span.

Seal balancing is therefore necessary to avoid disasters and to also elongate the life of a seal. Most seals are available in both balanced and unbalanced versions; both of which have their advantages and disadvantages. A balanced seal has a higher pressure limit. This means that they have a larger capacity for pressure and they also produce less heat. They can handle liquids that have a low lubricity better than unbalanced seals.

On the other hand, unbalanced seals are typically much more stable than their balanced counterparts as far as vibration, cavitation and misalignment are concerned. The only major drawback that an unbalanced seal presents is a low pressure limit. If they are put under even slightly more pressure than they can take, the liquid film will quickly vaporise and will cause the running seal to run dry and thus fail.

Pusher or Non-pusher

A pusher-type mechanical seal has a primary sealing ring which is put together using springs and a specially designed O-ring (See O-Ring mounted above). This dynamic secondary seal moves axially with the major seal face. The main purpose of a pusher seal is to make sure that the sealing fluid is spread across the face of the seal and that it does not leak out into the atmosphere. A pusher seal is most commonly used in low-temperature settings and in services that have light ends such as ethylene, methane and propane.

On the other hand, a non-pusher seal is made up of a bellows assembly (See Elastomer Bellows above). A bellow is a component of the seal that has two main functions. One, it performs the task of a load element and secondly, it also works as a sealing element. The bellow is the only thing that is needed in this type of seal to prevent any sort of leakage into the atmosphere. There is no use of the dynamic O-ring as the secondary sealing element is the bellow itself. Additionally, a non-pusher seal can also be used in high temperatures as “grafoil” secondary seals help non-pusher seal better handle the rise in temperatures, unlike the pusher type.

Single Spring/Multiple Spring

A single spring mechanical seal is a simple structure that does not require any complex method to be applied when using it. It simply acts as the transmission agent between the two systems in between which it is being used. They are designed as a simple design to take care of liquids that are contaminated. They have a naturally high resistance to pressure and heat which is what makes them suitable for use for a long period of time. Because of the simplicity of their design, they are very easy to assemble and dismantle.

Alternatively, the multiple spring seals are much more complex in structure and in their usage as well. They were initially designed for the chemical industry but their ability to provide an even loading to all seal faces has made them quite useful in almost all types of industries. Many seal and pump engineers regard multiple spring seals as the best.

Our Promise

Mechanical seals are a complex topic and the above information has been provided as an overview of the subject. All of our information is provided in good faith and should be used as a guide. If you have any queries please get in touch to speak to an expert, we will be happy to help.