8 replies to this topic

[rs20170808@gmail.com]

What should be the fail position of pump min flow line control valve? The pump min flow is routed to the suction tank? what should be the rationale for selecting fail position

[Bobby Strain]

I have always applied a philosophy that a control valve should fail closed unless there is reason to do otherwise.

 

Bobby

[Chemitofreak]

Hi,

 

I have a difference in opinion with the above answer.

 

Minimum flow line is provided on a centrifugal pump to save the pump from the following consequences:

1) Impeller damage

2) Overheating of casing and bearing

3) broken shafts etc, etc

 

The pump should always run above the minimum flow, hence the control valve on the minimum flow line shall have fail safe position as 'Open'.

 

Revert in case of any query.

[fallah]

What should be the fail position of pump min flow line control valve? The pump min flow is routed to the suction tank? what should be the rationale for selecting fail position

 

Hi,

 

The fail position of a minimum flow control valve should certainly be "Open"; because in the cases in which the discharge flow is going to be below minimum flow, the minimum control valve might has already been failed hence cannot compensate the flow shortage if it had been set to be failed closed...

[rs20170808@gmail.com]

hi fallah, 

 

thanks for your answer. your clarification makes perfect sense. 

 

one more ques. since we keep the control valve fail open. during emergency shutdown or esd case...so this valve will go fully open. 

is there a problem in that?

 

What should be the fail position of pump min flow line control valve? The pump min flow is routed to the suction tank? what should be the rationale for selecting fail position

 

Hi,

 

The fail position of a minimum flow control valve should certainly be "Open"; because in the cases in which the discharge flow is going to be below minimum flow, the minimum control valve might has already been failed hence cannot compensate the flow shortage if it had been set to be failed closed...

 

[rs20170808@gmail.com]

hello chemitofraek,

 

 

thanks for your answer. your clarification makes perfect sense. 

 

one more ques. since we keep the control valve fail open. during emergency shutdown or esd case...so this valve will go fully open. 

is there a problem in that?

Hi,

 

I have a difference in opinion with the above answer.

 

Minimum flow line is provided on a centrifugal pump to save the pump from the following consequences:

1) Impeller damage

2) Overheating of casing and bearing

3) broken shafts etc, etc

 

The pump should always run above the minimum flow, hence the control valve on the minimum flow line shall have fail safe position as 'Open'.

 

Revert in case of any query.

[breizh]

http://www.idc-onlin...atthewPaper.pdf

Hi ,

To  add to the discussion , the fail position should be open to protect the pump from cavitation , overheating .

 

my view.

Breizh 

[Chemitofreak]

 

hello chemitofraek,

 

 

thanks for your answer. your clarification makes perfect sense. 

 

one more ques. since we keep the control valve fail open. during emergency shutdown or esd case...so this valve will go fully open. 

is there a problem in that?

Hi,

 

I have a difference in opinion with the above answer.

 

Minimum flow line is provided on a centrifugal pump to save the pump from the following consequences:

1) Impeller damage

2) Overheating of casing and bearing

3) broken shafts etc, etc

 

The pump should always run above the minimum flow, hence the control valve on the minimum flow line shall have fail safe position as 'Open'.

 

Revert in case of any query.

 

It will not have an impact as the pump might also trip during the ESD.

[fallah]

 

hi fallah, 

 

thanks for your answer. your clarification makes perfect sense. 

 

one more ques. since we keep the control valve fail open. during emergency shutdown or esd case...so this valve will go fully open. 

is there a problem in that?

 

 

 

Hi,

 

There could be no problem in all situations such as ESD case; as the pump either recirculate (if still operating) the fluid through the kick back line or will trip following to ESD command...