Valve leak-test device

[MECE02]

There are some relief valves that could be leaking by into the relief flare header. We are aware of visual observations of valve leakage for propane/propylene such as ice balls around the valves. Are there any suggestions for devices to measure severity of the leak?

Previously used device includes:

Brand: THERMO Electron Corporation
Model: TVA-1000

Is there anything better that you have experience with?

Thanks!