On-Off Valve or Control Valve ?
On-Off Valve or Control Valve ?
(OP)
Hi, I'm currently working in a Gas Processing design and I'm a little bit confused in one subject.
So here is the case
I have two Feed Gas Scrubbers (upstream and downstream of Compressor). The Feed Gas is normally in 100% vapor form (no liquid flashing expected).
Bottom of these scrubbers will be discharged to close drain vessel. Each of them have a control valve installed to control the liquid level in the vessel.
As I mentioned before that the Feed Gas stream normally contain no liquids, what will be the best design for the control valve, an on-off valve OR a controlling one ?
The on-off valve will be opened if the liquid level reach HLL, then emptying the liquid until it reaches LLL in 3-5 minutes.
OR
Control Valve that will maintain the level of liquid in the vessel ?
Thanks
So here is the case
I have two Feed Gas Scrubbers (upstream and downstream of Compressor). The Feed Gas is normally in 100% vapor form (no liquid flashing expected).
Bottom of these scrubbers will be discharged to close drain vessel. Each of them have a control valve installed to control the liquid level in the vessel.
As I mentioned before that the Feed Gas stream normally contain no liquids, what will be the best design for the control valve, an on-off valve OR a controlling one ?
The on-off valve will be opened if the liquid level reach HLL, then emptying the liquid until it reaches LLL in 3-5 minutes.
OR
Control Valve that will maintain the level of liquid in the vessel ?
Thanks





RE: On-Off Valve or Control Valve ?
Many applications that would have been throttling in the past are going to on/off because of fugitive emissions concerns. A common way to do throttling is to have a continuous bleed that is throttled as the float moves up and down, sending a lower pressure signal to the control valve. This bleed is not a small amount of gas, so if you are using process gas for your control stream then you are putting that gas into the atmosphere. On the other hand if you are using control air there is an energy cost to the bleed stream.
David
RE: On-Off Valve or Control Valve ?
RE: On-Off Valve or Control Valve ?
A control valve will give you more options.
- How many times you need to drain the tank?
RE: On-Off Valve or Control Valve ?
For example, snap acting (on/off) type dump valves are perfered where drain lines could freeze off. A quick flush off fluids out the dump valve are less subseptible to freeze offs especially if the dump valve has an internally mounted stem and set, much like bib valves on your house if you live in cold climates.
Likewise, if you have a drain system that can not handle large swings in fluids, then steady continious dumping of liquids should used, ie throttling systems.