8 replies to this topic

[Abdullah_28]

Dear ,
1-When do we usually need to install minimum flow line for pumps!?

2-Does cooling water pump need Min.flow line !?
(Cap 360 m3/h. , power75 kw)
Thanks
Abdullah

[fallah]

Dear ,
1-When do we usually need to install minimum flow line for pumps!?

2-Does cooling water pump need Min.flow line !?
(Cap 360 m3/h. , power75 kw)
Thanks
Abdullah

 

Abdullah,

 

1-When there is a minimum stable flow for a pump below which the pump shouldn't be operated...

 

2-In general, yes...

[Saml]

Please, take a look at the following link.

https://www.ekwestre...f-minimum-flow/

 

Now, cooling water pumps are a special case in the plant. If you are in a continous process plant designed as usual you may be facing the following:

- Several exchangers with restricted outlet valve to regulate the flow per equipment.

- Perhaps the common return, or the return to individual cells are also restricted lo limit the maximum pump power, or to avoid flooding the decks.

 

Almost everything in cooling water flow control is manual, excep maybe a couple of special exchangers that may control cooling water flow automatically. If these exchanger can make your pump operate below the continous minimum flow where you get shorter pump life, yes, you need a minimum flow valve.

 

If not, the most common scenario is someone making a mistake and closing a big manual valve in the system. In this case a minimum flow valve is of relative value. Your plant is already down because of loss of cooling water and the bearings life of the cooling water pump is not as important.

 

What I have normally seen installed is a manual recirculation valve for pump startup.

 

Discuss the pros and cons inside your organization. Minimum flow valves are usually specified as fail open. So you have a recirculation valve, that would normally be closed  but when the valve fails will open and cause an upset in your process. You are adding this to protect the pump for an unlikely case of someone closing a manual valve, what would cause other problems beyond the reduced life of the pump.

 

But I am talking about my experience in continous process plants. You may be facing other reality.

[breizh]

Hi ,

Make sure the suction line of your pump is flooded and you have way to remove air to prevent air lock at the start .

 

 Breizh

[Abdullah_28]

Thanks all

But idont see a potential of low flow in cooling water because its closed loop .so flow will be circulated all the time!
As well as all valves are car seal open !
So correct me If iam wrong!

Edited by Abdullah_28, 13 November 2017 - 01:53 PM.

[fallah]

But idont see a potential of low flow in cooling water because its closed loop .so flow will be circulated all the time!
As well as all valves are car seal open !
So correct me If iam wrong!

 

Abdullah,

 

There may be zero cooling water demand case or a case in which cooling water demand is very low due to zero demand for most users; hence a minimum flow line between supply and return headers might be needed.

 

If there is really no potential of low flow and all valves in cooling water cycle are CSO; then it can be say no minimum flow line for pump protection is needed...!

[Abdullah_28]

But idont see a potential of low flow in cooling water because its closed loop .so flow will be circulated all the time!
As well as all valves are car seal open !
So correct me If iam wrong!

Abdullah,

There may be zero cooling water demand case or a case in which cooling water demand is very low due to zero demand for most users; hence a minimum flow line between supply and return headers might be needed.

If there is really no potential of low flow and all valves in cooling water cycle are CSO; then it can be say no minimum flow line for pump protection is needed...!

[Abdullah_28]

Dear fallah,
thanks alot
Umm, how water demand will be reduced ?
In our plant, most of lines are electrical traced
.
So I think for most of the users water demand will be same


By the way I have provide line at the end of header
For construction purpose (if they want to test the system before installing all users)

So can we take advantage of that line !?

[fahad shams]

Dear fallah,
thanks alot
Umm, how water demand will be reduced ?
In our plant, most of lines are electrical traced
.
So I think for most of the users water demand will be same


By the way I have provide line at the end of header
For construction purpose (if they want to test the system before installing all users)

So can we take advantage of that line !?

Dear Abddullah,

 

 

                          Usually there is a jump over line from cooling water supply header to Cooling water return header at the extreme ends of both headers, which is used during commissioning time for flushing the cooling water header keeping the users in isolated condition.

Once you confirm that all cooling water headers are flushed well than can you line up users one by one.

 

thanks