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Select The Pump For Split Piping System


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#1 duongbq

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Posted 10 May 2019 - 11:20 PM

Hi Everybody

 

I have process system as attachment, product is pumped by one pump from the tank, product is supplied to B and C with minimum requirement of flow rate and pressure. Please show me the solution to select the pump for system

 

Thanks so much,

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#2 thorium90

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Posted 11 May 2019 - 12:42 AM

Select a pump?

Your sketch shows the total flow to be 800*2 l/p and the pressure to be 3.5 kg/cm2.

Why not select a pump for a flow of 800*2 l/p and the pressure to be 3.5 kg/cm2? You can add any other headlosses required and have two control valves on each line to control the flow.

Do you have other considerations in mind?



#3 breizh

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Posted 11 May 2019 - 08:03 AM

Hi,

You should consider a circulation line at the discharge of the pump back to the tank unless there is no risk of overheating i.e always a flow passing either B or C

Good luck 

Breizh



#4 duongbq

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Posted 12 May 2019 - 11:23 PM

Thanks Breizh and Thorium90

 

This system has two pumps (one duty and one standby). To protect overflow I will design one discharge line back to the tanks. 

Total flow rate of the pump can be calculated by Q = q1 + q2 = 800 + 800 = 1600 l/p. 

To select total pressure of the pump, i need to calculated head-losses of system. The head-loss of discharge line = head-loss of line from pump to A + head-loss of AC or head-loss of AB?

 

Please give me the correct  



#5 breizh

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Posted 13 May 2019 - 12:38 AM

Hi ,

You need to size for the worst scenario meaning where you have the maximum head loss due to distance or fittings , etc ,

From the sketch it should be C .

Use the search engine in this forum to find calculator or tips to support your work .

If you have a re circulation line don't forget to take account the flow . Without any info , I will consider 20% of the supply to initiate the calculation.

 

note : what is the meaning of l/p ?

 

Good luck

Breizh


Edited by breizh, 13 May 2019 - 12:42 AM.


#6 Chemitofreak

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Posted 13 May 2019 - 01:36 AM

Hi,

 

First of all please clarify the units for flowrate i.e. l/p

 

Do you require flow control on both the destinations i.e. @ B and C ?, if yes then there should be a control valve on both the lines. If flow control is not required, then there should be a control valve on the non governing case destination to kill the excess pressure developed by the pump.

 

Since, both the destination pressure are the same i.e. 3.5 kg/cm2 (please note that you need to consider Pmax and not Pmin for pump hydraulics), the elevation and line loss will determine which is the governing case. Once, you find out the governing case, a control valve shall be installed in the non governing case to add pressure drop, so that the head for both the cases are the same.

 

If there are control valves on both the lines, then the pressure drop of governing case control valve can be considered as 0.7 bar (general thumb rule), and the pressure drop across control valve in the non governing case shall be compensated accordingly.   

 

Also, there should be a minimum flow protection line / re-circulation line from the pump to the storage tank. 

 

Revert in case of any query.



#7 duongbq

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Posted 13 May 2019 - 02:35 AM

Chemitofreak:

 

Sorry to all, the units for flowrate is LPM.  After checking again, the requirements on both the destinations B and C are as below:

 

Flow rate = qmin = 800 LPM; qmax = 1,000 LPM

Pressure = pmin = 3,5 kg/cm2; pmax = 7 kg/cm2

 

Operating system with two scenarios:

 

1. One pump supply product for one destination (B or C)

2. One pump supply product for both the destinations B and C at the same time

 

Due to economic conditions, we can not use flow control valves instead of using manual valves to change loss or select manual pressure control valve.

 

I don't have experiment to select the pump, please show me the solution step by step for more detail. 

 

For example if I choose flow rate of pump is 100 m3/h (1.666 LPM).  How can I calculate total pressure loss for overall system when pump out to both B and C?



#8 duongbq

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Posted 13 May 2019 - 04:43 AM

Hi Breizh

 

When the pump supplies product to B and C at the same time, maximum head loss is by head loss from pump to A (with flow rate q1 at B +q2 at C) + head loss from A to C (with flow rate q2 at C), is it?



#9 breizh

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Posted 13 May 2019 - 05:16 AM

Hi ,

You need to perform an hydraulic calculation of the system, meaning calculate the TDH vs the flowrate

To do so refer to the document I shared on the post related to "book for hydraulic calculation (zip file) ".

 

TDH = Discharge head -Suction Head

 

In your case it's a bit complicated because the discharge stream is split between B,C and the recirculation.

 

I've added a excel sheet as an example with multiple branches to support your work . more important is to understand the basic (Bernoulli theorem ) and to apply to your situation .

Another important point is the NPSHa calculation to get the right equipment.

 

I cannot offer more .

 

Good luck

Breizh

Attached Files


Edited by breizh, 13 May 2019 - 06:57 AM.


#10 Chemitofreak

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Posted 16 May 2019 - 02:10 AM


 

1) The pump should be designed from maximum destination pressure

 

2) If one pump is not going to cater to both the destination at a time, then it should be sized based on the max flow at destination B and C, also consider the relevant max destination pressure.

 

3) If one pump is going to cater to both the destination, then it should be sized based on the combined max flow max destination pressure of the both.. While carrying out hydraulics don't forget to consider combined flow (@ destination B & C) in common piping.

 

4) Last but not the least, you are not using control valve and will be using normal globe valve for controlling. For me, that is not a good idea, if you try to manually adjust the flow, you might not get the accurate flows

 

Revert in case of any queries






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