Do we need the min. flow re-circulation line..?
Do we need the min. flow re-circulation line..?
(OP)
We have the VSD driven LPG pumps(270 m3/hr & I/L pr=20 O/L pr=70 Kg/cm2 ).
As per the operation seq, disch. valve will start open after 50 secs & speed set has reached. For ex. if 2500 rpm, is set then disch. valve will start open after the pump reaches the 2500 rpm.
Valve opening time is 35 secs.
We feel that running the pump for this 1 min, with disch. valve closed, can create cavitation.so we can install one min.flow recirculation line.
Are we right...? do we need min. flow re-circulation line..?
As per the operation seq, disch. valve will start open after 50 secs & speed set has reached. For ex. if 2500 rpm, is set then disch. valve will start open after the pump reaches the 2500 rpm.
Valve opening time is 35 secs.
We feel that running the pump for this 1 min, with disch. valve closed, can create cavitation.so we can install one min.flow recirculation line.
Are we right...? do we need min. flow re-circulation line..?





RE: Do we need the min. flow re-circulation line..?
I doubt you need a recirculation valve.
It seems like you are doing many things wrong, many things without knowing why and wanting to do even more things, still without knowing why, dreaming up reasons partly based in some things you have heard, but don't understand even well enough to know what causes them, never mind how to prevent them. Isn't it time you found someone that knows what's going on around there?
We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky
RE: Do we need the min. flow re-circulation line..?
RE: Do we need the min. flow re-circulation line..?
Are you using 1 common VSD for all the pumps or individually controlled? And why do you need to use VSD?
RE: Do we need the min. flow re-circulation line..?
We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky
RE: Do we need the min. flow re-circulation line..?
We give the input speed in PLC, to get the required flow.
3 seperate VSD for each pump.
RE: Do we need the min. flow re-circulation line..?
RE: Do we need the min. flow re-circulation line..?
We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky
RE: Do we need the min. flow re-circulation line..?
No suction pr drwing much.
This is the operation seq set already..But i dont know y so...?
We just give the start command, after setting the speed.
1)Aux LOP start
2) after 30 secs pump speed start to increase & cooler fan starts.
3)after 20 secs MOV start opening.
so total 50 secs.
I dont know y we start the pump in disch. valve closing position.
RE: Do we need the min. flow re-circulation line..?
In any case, I wouldn't think that you'd normally get any real problems from that, if you can manage to hold the total time to under 1, or even 2 minutes.
We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky
RE: Do we need the min. flow re-circulation line..?
In you later response it seems it is by time setting.
Actually the MOV start to open 20sec after the the main pump started to turn. The first 30 sec only the aux. LOP is running to pre-lube the pump / motor bearing.
Are you saying that you have to set the speed and hence the flow rate every time before you start the pump operation?
There is a NRV in each of the pump discharge, so starting with opened discharge isolation valve is not an issue even with back pressure.
How often do you have to start/ stop the pumps?
RE: Do we need the min. flow re-circulation line..?
Just try working with your permissives in your PLC. You can change start-up sequences and or shave off some time at each step. take notes as to pressures and flows etc..