3 Way Valve Drain Port "Vent"

Greetings,

In the liquid fuel system in our power plant, there is a 3 way valve in the turbine compartment that direct either purge air or diesel based on what fuel the turbine is burning.

My question is that there is a drain port in the valv,e and it is stamped "vent". this line goes to the false start drain. what is that benefit of this port? Could you elaborate please? and thank you.
 
If the 3 way valve is a pilot (operates by air another larger valve), it has to have a vent to let the air out (let it bleed to zero).
 
>What does the P&ID indicate the vent is for?

Well, I am not sure, but maybe the vent air well help pushing the liquid in the drain line, to the false start drain.

see the picture in the link. the vent is the blue arrow and the distributor drain is the red arrow. after that they will combine and go to the false start drain.

https://postimg.org/image/9ho82uu4r/
 
> If the 3 way valve is a pilot (operates by air another
> larger valve), it has to have a vent to let the air out (let
> it bleed to zero).

thank you, yes the valve is operated by air. this valve has a test procedure to insure the valve is working properly. it is written that the pressure of pilot air that will actuate the spool is 125psig, and if some air vents out this will be normal.
 
Aptx4869,

I believe the "vent" is actually like a packing leak-off, so that if any liquid fuel leaks out along the valve stem it will go to the gas turbine drains tank, instead of leaking into the turbine compartment where it might contribute to a fire or explosion.

Many years ago, and for decades prior to that, the gas fuel Stop-Ratio Valve and Gas Control Valve packing leak-offs were piped out of the Gas Valve Compartment to atmosphere--to prevent the accumulation of combustible gas in the gas valve compartment should the valve packing leak. I believe this is very similar.

I also believe the reason the valve is shown in dotted lines is because it's really shown in solid lines in ML 0477, the Fuel Purge P&ID. So, there may be more detail there.
 
M
Hi APTX4869,

It would be much easier if you post complete picture of this page, not selected portion only.

Anyhow, as far my experience there are check valves in purge air line that restrict oil flow towards purge lines (When turbine is running on liquid fuel), in-case check valves have some problem to close completely (small quantity of fuel will continue to flow towards purge system), this drain line will direct that oil towards false start drain tank through this vent/drain/port.
 
Dear CSA,

thank you for your explanation. Sounds logical.

Any oil that leaks from the flow stream into the valve body will be drained to the false start drain instead of leaking into the turbine compartment.

Thank you again
 
muz_sindhu,

thank you for your reply. it's a 3-way valve instead of the conventional check valve. I think CSA explanation is logical, please take some time to read it.

Thank you again
 
Top