1 reply to this topic

[Supriyo Mukherjee]

Dear All,

 

I was currently studying a screw compressor for air compressor -oil flooded type.
Attached is P & ID with legend.

 

I was having a doubt regarding its control system.

 

This compressor can work in two mode-1. Idle.2. Load mode.

 

In idle mode the inlet valve(2) remains closed and  vent valve(19) remains open.

 

As soon as the machine is directed to load from its HMI panel the inlet valve opens(2) and the vent valve opening is controlled by pressure of air ex-compressor.

 

My basic doubt here is what operates the vent valve and inlet valve. As we can see a connection of air through a control valve(18)and also a 3/2 directional control valve(24.4)(It is said in legend it amplifies volume of control air from inlet valve). I asked the vendor about how the valve(inlet valve-2) is being operated is it by current only? They said yes.
But looking at P & ID and legend it becomes quite believable that there is air supply to the valve.

 

 

If I believe that the air is taken from ex compressor outlet to control the valves, that raises two more questions

 

1. At start from "stop to idle" there is no air --how does vent valve open when compressor is started in idle. Also when the compressor is changed from "idle(unload) to load" there is no pressure available, so how does the valve open when machine is just loaded.

 

2. Also the outlet air from compressor is moist .

 

I am basically perplexed at this juncture hoping someone with their experience with these kind of compressor could help me out in deciphering the control valve's action.

 

Also when this compressor is started there is no separate instrument air available nor used.

 

 

Regards,

 

Supriyo Mukherjee

 

 

Attached Files

•  CSD_P&ID.pdf   717.94KB   15 downloads

[Supriyo Mukherjee]

Can Anyone reply me on this issue??