Disc springs - fittings
The addition of plate spring kits (live loading) under the bolts of the valve's compression glasses is advantageous for fittings that meet at least the following two conditions:
- Sealed with a sealing cord
- High number of open/close cycles
- Operated by actuator
- Poorly accessible
- High media pressures and temperatures
- Fittings on critical applications
- Historical leakage problems
- Monitored fittings for emissions
Plate springs have specified mechanical properties depending on the dimensions (inner and outer diameter, thickness and overall height) and the material from which they are made.
Their benefits are:
- High axial force, low deformation
- No permanent deformation or relaxation under the designed load
- Long service life
- Easy adjustment of the desired mechanical properties by assembling into sets
Disc springs are capable of operating at temperatures from -240 to +590 °C
depending on the material type. The choice of material depends on the application, the environment and the temperature in which they will operate. Some disc spring materials are susceptible to corrosion cracking, which is prevented by selecting the appropriate material and spring finish.
Different ways of arranging sets
- One spring as standard
- Two springs in parallel
- Two springs in series
- Two springs in series/two in parallel
Each spring has a given load-deflection characteristic. By combining the arrangements, we can vary the deformation or load (e.g. two springs in series arrangement will carry the same load at twice the deformation).
Plate springs help designers solve the problems of vibration, differential thermal expansion, relaxation, creep (bolt creep) with the simultaneous lack of space. They create and maintain a controlled amount of pressure on the packing.
The advantage of a properly designed set of springs is that they compress the goggles even when the volume of the goggle rings decreases
(by relaxation, extrusion, friction). When the volume of the seal is lost, the springs expand slightly, the force on the glasses is slightly reduced, but the decrease in force is significantly less compared to a packing chamber without a set of springs. However, despite the slight loss of pressure, the preload on the sealing cord is safely above the leak class level (minimum pressure on the sealing cord for a given leak). The tightness of valves equipped with disc spring sets is many times longer.
In addition, the time required for the first adjustment (tightening of the packing goggles) is dependent on the quality of the seal and its installation.
In the case of valves with a high number of openings and closings, the sealing rings wear out quickly and float out of the sealing space. This causes the pressure on the seal to drop rapidly and the medium begins to leak. This problem can be solved either by frequent tightening of the packing or by adding a set of disc springs.
If the fitting was not equipped with disc springs
, it would be necessary to tighten 5 times to achieve the same tightness
. The kit contains the disc springs in the suggested arrangement
and number ready
for immediate installation
, sets of sealing rings according to the type of medium and installation instructions.
Pokorny industries designs and supplies sets of disc springs and packing rings for valves including assembly instructions, calculation of tightening torques and friction force.