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Pump Flow Switch


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#1 farid.k

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Posted 29 July 2013 - 10:36 PM

hye there,
 
i am a newbie in this forum.
 
i do have one simple question regarding pump flow-switch. where i supposed to put the flow switch? is it at pump discharge or pump suction? normally, by previous design, pump switch located at pump discharge. but for my case, the liquid transfer is from lorry tanker to a vessel. and normally tanker dont have low low level and they will transfer all the liquid to the vessel and there is chance for the pump to suffer (run dry). i dont think by locate the flow switch at pump discharge will protect pump from run dry. so i re locate the flow switch to pump suction. any comment from the senior?
 
thank you


#2 RAM1975

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Posted 30 July 2013 - 01:05 AM

Hello, 

 

 

It is very important to know what fluid you are transfering from the tanker.

I would like to give you my example we are transfering furnace oil from tanker to vessle. we have break tank between these two .

Tankers are unloaded between the small tank. the pump suction is connected to this break tank and then fluid is transfered.

But pls check in your case if its solvent or other flamable liquid which requires other safetyes to be considered.

ajay



#3 farid.k

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Posted 30 July 2013 - 01:54 AM

Dear ajay,

 

 

thanks for the reply,

for my case, i dont have any break tank in between lorry tanker to the vessel. i just directly transfer the liquid from the lorry tanker to the vessel. the fluid properties are as below:

 

name: liquified poly-propylene

vapor pressure: 12.10 bar(a)

density: 500kg/m3

viscosity: 0.09 cP

Flammability: highly flammable

 

so, based on the info given, how does the properties of the fluid relates to the flow switch* location?

 

*the flow switch is just to protect pump from run dry.

 

 

tq



#4 Erwin APRIANDI

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Posted 30 July 2013 - 03:36 AM

Hi bachik_syes@yahoo.com,

 

First of all pump flow switch is mostly put on the pump discharge, because in most application the pump are protected from runnning dry by having a low level switch on the pump tank suction which protect the pump from running dry. So the use of flow switch is to protect the pump from running lower than minimum specified flow.

 

In your case, I see it like a batch process in your case where you are transfering the liquid from Lorry tanker to a vessel. I've seen the usage of Flow Switch to protect the pump from run dry, but to be very carefull with the set point, it should be corelate to the min static head available in the lorry tank in order to prevent pump run in dry condition.

 

In case of very sensitive situation, where pressure/flow switch is unable to be apply and pump run dry can lead to major safety I would preffered to use buffer tank, in between the Lorry tanker and the pump, with a low level switch protection in the buffer tank and to always manned the transfer operation.

 

In other case that I have seen other just put a sight glass on the pump suction pipe and to always manned the transfer operation (this is for stabilized condensate pump transfer)


Edited by erwin.apriandi, 30 July 2013 - 03:39 AM.


#5 manchester

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Posted 30 July 2013 - 09:45 PM

 

 

Bachik,

 

I would prefer to put Pressure Low Switch in your pump suction, rather than Flow Low Switch.

 

The reason: The intention is to protect pump from cavitation. And to prevent cavitation, you need to have sufficient NPSHA which > NPSHR.

 

And to ensure you have sufficient NPSHA, you need to monitor liquid level or suction pressure

 

In case of yours, where you don't have level switch, you may replace it with PSL.

 

Provision of FSL in suction, IMHO, is also can be done. However, unfortunately, you cannot ensure pump will not get damage if you only monitor flow, without ensuring sufficient suction pressure. 






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