WVC France Introduce GRAB (Graphite Ring Adjustable Brake)

The vibration problems occurring on discharging relief valves (liquid application) located at the extremities of piping have been well-known for decades. During opening and discharging, the relief valve may vibrate or chatter.

Vibrations are oscillatory movements of the internals (disc) with high velocity and small amplitude.

Chatterings are movements of internals (disc) with low frequency but with such amplitude the valve will oscillate between closed and opened positions.

Damping systems with fluids have been used in the past. Due to maintenance issues and high costs of this system, it has been necessary to find another solution.

Weir Valves and Controls France discovered the best choice to avoid instability risk is the use of friction.

WVC France has developed a patented system, (patent number 0700890) named GRAB. This is a damping by friction on the spindle’s top end of the PSV. This innovation is coming from the SEBIM know-how and R&D for the nuclear valves, on which graphite rings are used on austenitic stainless steel for improved guidance. This know-how is used, not only to avoid the seizing, but to avoid any jamming as well.

The GRAB system is adjustable on the top of the valve and is composed of pure graphite braking rings with chamfered edge, auto-adjustable in terms of braking, with the use of a spring; compressing the rings against the spindle.

The various performances of the system are as follows:

-          no risk of vibration nor chattering.

-          no alteration of the set pressure out of the allowable tolerance norms

 (ASME Section VIII div.1, ISO 4126).

-          Full lift at the overpressure stated in the norms.

-          No impact on the valve tightness.

-          No risk of seizing or jamming.

-          Auto-adjustable rings (to compensate the wearing away of the graphite)

-          In situ setting if necessary.

-          Maintenance free.

-          Adjustable on an existing valve with modification on the cap only.

-          No problem even if the valve is equipped with a lever, limits switches or test gags.