Can Leakage from Gate Valve Packing Drain Downstream Isolated Piping Section?

[invent11]

We have 2 normally closed valves installed on a water line in our plant. One horizontally installed 6" Gate and another 6" globe valve downstream of it. Pressure upstream gate valve is 500 kPa(g). The isolated section of piping between these valves are filled with water at atmospheric pressure (i.e this section was fist filled with water from upstream then pressure brought to atmospheric by opening and closing a vent valve).
My question is in case of any future 6" gate valve packing leakage. can it drain the isolated section (between the valves)?
In other words the leakage source can be EITHER upstream OR lower stream of gate valve independent of their pressures and only is related to the leaking spot on packing or other factors are involved?
Thanks for your input

 

[Danlap]

No, it cannot (completely) drain your pipe-spool between both valves. But never say never.
Leakage rate is simply due to two things: there is leakage path and Delta P.

I am not really sure what you mean with 'horizontally installed', does stem orientation is horizontal OR valve horizontal yet stem is vertical (gland packing facing upwards)?
I am just thinking out loud for some logic:
- Gland is tight, leakage rate on wedge gate valve meaning sealing area (Seat vs wedge) side A (upstream) and side B (downstream) are already damage/compromised.

- Leakage from gland meaning that gland is damage/compromised and top cavity is pressurized wrt atmospheric pressure.
Sources for pressurized cavity meaning either Side A is compromised or side B is compromised and/or both sides are damage.
To drain water on side B, for simplification, meaning that side A, globe valve and drain valve are completely tight whilst gland and side B are completely damage

So the only triple jeopardy that could contribute to drain the volume are (all scenarios should happened at the same time):
- gland facing downwards, just for the sake of water gravity. Otherwise (for ergonomically installed valve) atmospheric air pressure outside gland will be will be equal to pressure within the valve, hence no flow through gland
- gland completely damage --> 500 kPa with all due respect is not much, gland leakage within this range normally happened gradually and not bursting. Even this condition should be noticeable by daily operator
- Seat B is completely damage whilst Seat A and Globe valve are completely tight --> wrt your description, it is highly unlikely that Seat B (downstream, not 'directly' facing flow) will have worst condition compared to Side A and/or globe.

Regards,
MR

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[invent11]

Thanks for input