17 replies to this topic

[farid.k]

Currently there is an argument for the minimum flow line for transfer pump (centrifugal pump). Related info is as per below:

1. The transfer is from a mobile tanker to an atm storage tank.
2. Transfer time is about 2 hours and will be guide by operation.
3. Pump flowrate: 10 m3/h
4. Discharge pressure: 5-6 barg.

 

Argument:

1. For pump protection, I do proposed to have relief valve at discharge, set at shut off pressure or less than that. PSV discharge will be at pump curb and open drain before goes to treatment (since the PSV flow is small [should be 5m3/h or less] and service is not critical and toxic). Basically, the reason to consider relief valve is because if I do consider minimum flow line, I have to route back to the suction which is not good practice. Plus, I need to resize the pump, motor, piping and etc. since minimum flow line using orifice. And by using relief valve, it still can protect the pump in case of shut off condition.
2. Consultant said, centrifugal pump highly preferred to consider minimum flow line for pump protection. It will be rout back to pump suction and should be ok. PSV is not recommended and normally use with PD type pump.

 

Question:

1. Is it PSV valid for pump protection in case of block discharge or shut off pressure?
2. What is another impact (other than undistributed heat in the system) if we have minimum flow line that goes to the suction?
3. Which one is the best method?

 

thank you

[AlertO]

hi farid

 

To have a psv setting at the pump shut-off is not the protection for maintaining minimum flow for the pump because the psv will open at flow = 0 and when the fluid is start to flow through PSV, the pressure will drop and then PSV will be closed. After that the PSV will open and close again and again. This create the damage risk to both pump and PSV.

 

To have minimum flow to the suction line is sometime necessary if we have no other choice. Considering to have some alarm i.e. flow at pump discharge can help operation to solve the problem before the pump is over heated.

[fallah]

farid.k,

 

1- For centrifugal pumps isn't a good and reasonable practice, but if the downstream discharge line not to be designed for pump shut off pressure; a PSV would normally be considered for downstream facilities protection even if the system have already been equipped with minimum flow protection...

 

2- Another impact is considering higher capacity than needed for pump due to adding flow of recirculating minimum flow to the pump capacity...

 

3- The best is considering minimum flow back to the suction drum while the downstream facility being designed based on pump's shutt off pressure...

[breizh]

farid ,

Why not just adding a liquiphant ( E&H ) or fork  at the suction of the pump which will cut off the pump?

 

Breizh

[farid.k]

hi farid

 

To have a psv setting at the pump shut-off is not the protection for maintaining minimum flow for the pump because the psv will open at flow = 0 and when the fluid is start to flow through PSV, the pressure will drop and then PSV will be closed. After that the PSV will open and close again and again. This create the damage risk to both pump and PSV.

 

To have minimum flow to the suction line is sometime necessary if we have no other choice. Considering to have some alarm i.e. flow at pump discharge can help operation to solve the problem before the pump is over heated.

Dear alerto

 

Thanks for the reply,

 

I think minimum flow line that use auto recirculation valve also has set pressure and the working philosophy is just like relief valve (it has internal spring just like psv) whereby when it reached the set pressure, it will open and recycle back to the tank. Do you think this two items working philosophy is same? If same, it also will be open and close just like PSV. Any comment?

 

 

farid.k,

 

1- For centrifugal pumps isn't a good and reasonable practice, but if the downstream discharge line not to be designed for pump shut off pressure; a PSV would normally be considered for downstream facilities protection even if the system have already been equipped with minimum flow protection...

 

2- Another impact is considering higher capacity than needed for pump due to adding flow of recirculating minimum flow to the pump capacity...

 

3- The best is considering minimum flow back to the suction drum while the downstream facility being designed based on pump's shutt off pressure...

 

Dear fallah,

 

Thanks for the reply,

 

Currently we pumping from isotanker to an atmospheric tank. We cannot route back to the isotanker and also try to avoid to route to the suction. Is it ok to route to atmospheric tank?? Yea, it is kinda weird but we try to eliminate to route back to the suction.

 

farid ,

Why not just adding a liquiphant ( E&H ) or fork  at the suction of the pump which will cut off the pump?

 

Breizh

Dear briezh

 

Thanks for the suggestion,

 

I never heard liquiphant ( E&H ) or fork. Kindly explain how it work. I do have some previous project (same working philosophy whereby to transfer from an isotanker to a sphere tank). I do consider flow transmitter at the pump suction and the transmitter will off the motor when the flow decreased up to minimum flow. Is it same to the flow transmitter? Do you have picture for the fork?

[breizh]

https://www.google.fr/#q=liquiphant

 

just provide a T to install the sensor (switch) at the suction line of the pump .  Similar to no flow detection .

 

Breizh

[farid.k]

https://www.google.fr/#q=liquiphant

 

just provide a T to install the sensor (switch) at the suction line of the pump .  Similar to no flow detection .

 

Breizh

so by considering this, i think we dont need the minimum flow line i guess? since when there is no flow, the pump motor should be trip right?

[breizh]

farid ,

 

Yes .

The topic is about draining an Isotank (Mobile tank) . The fork is submerged with product when you line the isotank to the suction line of the pump . As soon as the isotank is empty , taking account the volume in the pipe line , the fork is becoming dry and generates a contact ( LSL or FSL) to trip the pump.

Breizh

Edited by breizh, 23 December 2014 - 09:48 AM.

[fallah]

As far as i know, liquiphant is a liquid level switch not to be affected by flow; and when is mounted on pump's suction line just functions as an empty pipe detection and pump protection for dry running, then nothing to do with minimum flow detection where the flow lower than a prespecified value should be sensed...

Edited by fallah, 23 December 2014 - 03:00 AM.

[farid.k]

As far as i know, liquiphant is a liquid level switch not to be affected by flow; and when is mounted on pump's suction line just functions as an empty pipe detection, then nothing to do with minimum flow detection where the flow lower than a prespecified value should be sensed...

i think should be flow transmitter right?

[fallah]

Farid.k,

 

Yes, in ddition to minimum flow line along which an RO or a control valve is applied to release the minimum flow back to the suction drum, there should be a dedicated flow element/transmitter at the pump's discharge line triggered on LOW LOW LIQUID FLOW to trip the pump when there is a malfunction in operation of minimum flow line...

Edited by fallah, 23 December 2014 - 02:58 AM.

[farid.k]

Farid.k,

 

Yes, in ddition to minimum flow line along which an RO or a control valve is applied to release the minimum flow back to the suction drum, there should be a dedicated flow element/transmitter at the pump's discharge line triggered on LOW LOW LIQUID FLOW to trip the pump when there is a malfunction in operation of minimum flow line...

in addition to minimum flow line? what if i just add the flow transmitter, and set pump to trip at minimum flow and by having this i remove the minimum flow line. having two protection for me is redundant. i just want to make the system simple and reliable. previously they just transfer using gravity flow.

[fallah]

Farid.k,

 

It's up to you and the relevant project specifications and requirements will dictate to consider one or more layers of protections. Considering only minimum flow line makes the system more simple but in the case of, let say, control loop malfunction in minimum flow line leading to control valve closed while needed to be open, there would be no protection for the pump against shut off or a flow lower than prespecified minimum flow value...

[AlertO]

Farid

 

Your system is quite simple and the operation is intermittent. Maybe, only min flow line is sufficient. To have more reliability, adding low flow alarm provide at pump discharge warning your operators is recommended.

 

 

Answer to your question, ARV doesn't same as PSV. It always open allowing fluid pass through during normal flow operation. When the liquid flow is reduced to below pump minimum flow, the valve will be closed and bypassed to min flow nozzle which is restriced for min flow rate only. In additon, ARV operation doesn't relate to the pump shut-off pressure as well.

[farid.k]

Farid.k,

 

It's up to you and the relevant project specifications and requirements will dictate to consider one or more layers of protections. Considering only minimum flow line makes the system more simple but in the case of, let say, control loop malfunction in minimum flow line leading to control valve closed while needed to be open, there would be no protection for the pump against shut off or a flow lower than prespecified minimum flow value...

have you experience the pump motor overload trip? of low amphere trip due to low flow?

[farid.k]

Farid

 

Your system is quite simple and the operation is intermittent. Maybe, only min flow line is sufficient. To have more reliability, adding low flow alarm provide at pump discharge warning your operators is recommended.

 

 

Answer to your question, ARV doesn't same as PSV. It always open allowing fluid pass through during normal flow operation. When the liquid flow is reduced to below pump minimum flow, the valve will be closed and bypassed to min flow nozzle which is restriced for min flow rate only. In additon, ARV operation doesn't relate to the pump shut-off pressure as well.

Yea, it is not same. Just that for me the working philosophy is quite the same since it is spring operated just like the relief valve. Why you said doesn’t relate to the shut off pressure? Yea, it does because, by having that ARV, the pump never run at shut off pressure. Without ARV, the pump has potential to run in shut off pressure. If I not mistaken, the ARV itself has its set pressure and set below the shut off pressure.

Do correct me if I were wrong.

[fallah]

farid.k,

 

Pump's motor has its own protection against overload. In fact, a motor protection relay is designed such that protect motor from overload, excessive heat, phase loss, excessive operational cycles,....

 

If there would be no low flow signal to trip the pump, motor protection relay can't do the job...

[AlertO]

farid

 

ARV is flow sensitive device not same as PSV. At normal flow the flow will pass through the ARV (main line), but when the flow is reduced (pressure is higher) the valve will be closed which is reversed action compared with PSV.