Mobile ring sealing: is D-ring the ideal solution at low pressure?

26/02/2015 - posté dans Experience

Is D-ring the optimal answer to all mobile ring sealing issues? Not necessarily.  
We would like to share our experience on low pressures applications.

As required by a Hydro Power Customer, PXL SEALS proceeded to a mobile ring sealing of a spherical valve initially equipped with O-ring seals. Customer requirement was to optimize movable ring sealing by using D-ring profiles. D-ring profile is designed to increase the seal stability in gland (squared base) preventing twisting failures. This type of failure is typically reached by O-ring profile. Phenomenon of twisting damages seals.

Constraints were the following:

  • Low working pressure

  • No differential chamber

  • Dam raw water

  • Temperature from 1 to 20 °C

Further to the maintenance, the customer had movable ring mobility issues: operating time was too long compared to initial values. Another valve (security valve) had to be closed to allow the ring mobility (over pressure created by closing the security valve)!

It was critical to find a solution to allow the mobile rings quicker movement and ensure security. Moreover sealing failures reached by customer was not due to mobility but it was due to twisting failures. Consequently, PXL SEALS studied the failure reasons.

After analyzing the seal behavior using FEA simulation, we realized that the D-ring generated high friction. We found out that D-rings generate a higher friction value than O-rings at low pressure (0 < pressure < 3 [MPa]). This explained the slow mobility of the equipment.

Friction was caused by the D-ring design. Due to its squared base, D-ring generates more contact pressure than an O-ring at low pressure. And more contact pressure equals more friction (using a similar material)!

Consequently, we proposed an alternative solution, a X-ring profile, that guarantees the sealing stability in the housing and significantly reduces friction at low pressure. X-ring has the same behavior (friction, pressure tightening) as the O-ring especially at low pressures levels. Furthermore, the solution suits to any of existing housing, without any modification needed.

Thanks to his experience and his expertise in Hydro applications, PXL SEALS finds solutions to answer specifically to his customers’ critical issues.

Tags : Mobile, ring, sealing, seal, seals, D-ring