What is a "Self Venting Plug"???

[benzy4]

A Custumer ask me a Self Venting Plug on a valve equipped with low emission packing.

This Plug help to measure the lakage rate of the valve packing.

I really don't know that it is.
Do you know?

Thank you

 

[MortenA]

I think it means a relief valve that reduces the build up overpressure in the body cavity - not into the open but to the low pressure side of the valve when closed so that the upstream pressure will act with full force on the valve seats.

I believe that for ball valves you choose between single pistion or double pistion seats (for tunion mounted balls).

Best regards

Morten

 

[NGiLuzzu]

May be one or more theaded (pluggable) holes on the valve neck in correspondance with one or more lantern rings among the packing rings?

Perhaps others call this option "Packing Flushing", as it allows to suck of flush the possible leakage away...

Hope this helps, 'NGL

 

[roydm]

Sometimes a valve in certain service needs to relieve with temperature change e.g a ball valve on liquid chlorine service,
I quote
"Ball valve design must ensure that excess pressure, resulting from expansion of liquid trapped in the ball and body cavity when the valve is closed, will relieve spontaneously in the direction of the higher line pressure. This relief may be accomplished by providing a relief hole in the ball, providing a passagein the body to the high pressure side, or by using cavity pressure self-relieving seats"
If your liquid has unusual thermal expansion properties perhaps thats what the client is aluding to.
Roy

 

[JimCasey]

I think roydm is onto the intent of what the customer requests. Durco calls it an "upstream relief hole" for their plug valves. If a liquid is trapped in the cavity and then vaporizes, the pressure can be enough to exceed the valve's rating (or worse). Drill a hole between the cavity and the upstream port, and the pressure in the cavity can never exceed the upstream pressure. Referenced low-emission packing would be appropriate for the liquid chlorine service that roydm mentions.

However, the vented plug will NOT help measure the leakage of the valve packing.

A vented BONNET, with lantern ring double packing, WILL let you measure the packing leakage rate, because any leakage that gets through the bottom packing rings will flow out the bonnet vent where it can be measured and directed to a safe reclamation point. The upper packing set will keep anything from making it to the environment.