Live loading provides a constant load over the life of FEC packing set and other critical packing applications (e.g. mixers and kneaders) and therefore helps to maintain lowest leakage levels. This greatly reduces or, in many applications, helps to eliminate your need for packing box adjustment and reduces maintenance.
While many Burgmann Packings FEC products can be used without live loading systems, without compromising product performance we recommend to consider live loading for extreme service applications. In order to get your customized live loading system please reach out to Burgmann Packings Engineering team.
- Sealing Set (compression rate)
- Type of application (valve or mixer)
- Dimensions (stuffing box, surrounding)
- Compression Force (bolts, spring set)
The Burgmann Packings live loading system is a special arrangement of disc springs combined with a stainless steel protection sleeve for Valves, especially control valves, thermal cycling applications and critical nuclear and low emission service.
- Defined compression by customised spring stack
- Sleeve acts as protection for springs
- Springs are guided by the sleeve and not by the bolts
- Gap indicates constitution of packing set
- Ideal compression easy to initiate by gap between sleeve and gland
- Extended service life for FEC packing set
Live Loading for Valves
Throughout the service life of a packing set, the compression load on the sealing system will vary with time, due to relaxation of the packing rings and bolt materials, temperature and pressure cycling, vibration etc. To offset these changes, systems are sometimes used in order to provide a more constant load over time by altering the elasticity of the assembly. This can be achieved by using longer fasteners (with spacers), or live-loading. The latter is usually provided by metal disc springs (often called “Belleville washers”), which are carefully engineered, selected and arranged to provide a known load, so limiting the clamping force in the system.
Effectively, the disc springs are compressed to a specific deflection of load at flat. This offers a form of stored energy as a live-load, and is converted to a compressive load on the flange, and hence, onto the packing. Very careful consideration must be given to the amount of live-loading applied, since it may lead to excessive pressure on the gland and packing. When working as a stack, the design usually allows for a maximum disc spring deflection of around 75% compression of its uncompressed shape (such that the spring retains 25% of its uncompressed shape). Applications may have disc springs stacked in series, parallel and combinations of both. Each combination provides a different level of stored energy under deflection.
Regardless of configuration, the stack of disc springs requires a guide, on the inside or outside diameter, to prevent lateral movement under load. When an outside encasement is used, this can also protect the system from environmental corrosion, adding the advantage of maintaining constant lubrication provided by a high-pressure grease. Alignment of the disc springs and lubrication minimises friction between the contact surfaces. While providing a means of containment, the external encasement may also offer a security lock, to prevent misuse or alteration of the original design, adding to plant operational security. Note that the grade of steel employed may limit the maximum operating temperature of the live loading system.