I have seen that in some emergency shutdown application is recommended to use a double block and bleed valve arrangement.
Could somebody tell me if each solenoid is connected to a different output channel in the control system or if it possible to use the same output channel to energize both solenoids for the two block valves?

Thanks,

Sergio

 

Good question. I have seen this implemented several different ways.

1. seperate solenoid valves with seperate outputs for each of the 3 valves. this allows the bleed valve to be closed first, than the block valves opened so no chemical comes out the bleed valve.

2. seperate solenoid valves with a single output that first energizes the bleed valve, than once the limit switch closes, power flows through the limit switch to open the block valves.

3. a single output with three seperate solenoid valves.

4. a single output, and a single solenoid valve.

I have also seen schemes where after the chemical injection is complete that the bleed line is flush out with water via another valve. Obviously there are cases where this is totally inappropriate.

The thing is, I think you have to look at your specific case and determine just what is appropriate in this specific case. it may well be different for different instances.

 

Sergio,

It would certainly be possible to have one digital output that provides power to operate the two energize to open block valves and one energize to close bleen valve. To allow gas to flow the output is energized. De-energizing the output, and a failure of the power source, would cause the flow to stop.

John Shaw
http://www.jashaw.com/pid