Disc springs - fittings

The addition of plate spring kits (live loading) under the valve's eye bolts is suitable for valves that meet at least the following two conditions:

• Sealed with a packing cord
• High number of opening/closing cycles
• Operated by an actuator
• Poorly accessible
• High media pressures and temperatures
• Fittings on critical applications
• Historical leakage problems
• Monitored fittings for emissions

Disc springs have specified mechanical properties depending on the dimensions (inner and outer diameter, thickness and overall height) and material from which they are made.

Their advantages are:

• Space-saving
• High axial force, low deformation
• No permanent deformation or relaxation under the designed load
• Long service life
• Easy adjustment of 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 choosing the appropriate material and spring finish.

Different ways of arranging sets

1. One spring in series
2. Two springs in parallel
3. Two springs in series
4. Two springs in series/two springs in parallel

Each spring has a given load-deflection characteristic. By combining the arrangements, we can vary the deflection or load (e.g. two springs in series will carry the same load at twice the deflection).

Plate springs help designers solve problems of vibration, differential thermal expansion, relaxation, creep (bolt creep) with the current lack of space. Creates and maintains a controlled amount of pressure on the seal.

The advantage of a properly designed set of springs is that they compress the packing goggles even when there is a loss of packing ring circumference (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 drop 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) depends 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 valve was not equipped with disc springs, it would be necessary to tighten 5 times to achieve the same tightness. The kit includes disc springs in designed arrangement and number ready for instant installation, sealing ring sets according to the type of medium and installation instructions.

Pokorný designs and supplies disc spring and packing ring sets for valves, including installation instructions, calculation of tightening torques and friction force.