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Risk Of Blocking For Two Positions Three Way Valve.

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#1 Jalalirad


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Posted 08 July 2020 - 04:09 AM

Hi every body, 


In my system there are two pumps. The discharge lines come together and a relief valve is installed on the jointed discharge line to ensure the maximum pressure pressure on set pressure (= MAWP of pipe). Now I want to install two two-positions Three-Way-Valves on each discharge. Because sometimes the flow shall be conducted to another plants. 

two-positions Three-Way-Valve  means there are two choices for the valve (right or left directions). There is not any other option e.g. blocking the lines. If one way is closed the other way is opened in the same time. The valve are manual. 


My question:

Is any risk of blocking the lines and over pressuring the discharges? I mean shall I think about the fail close of the valves?

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Edited by Jalalirad, 10 July 2020 - 04:32 AM.

#2 fallah


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Posted 08 July 2020 - 06:43 AM



Please upload a simple sketch of the system you described...

#3 Bobby Strain

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Posted 08 July 2020 - 09:05 AM

And what fluid is handled.

#4 Jalalirad


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Posted 10 July 2020 - 04:30 AM

It is uploaded. The fluid is NaCl 30%.


The red lines are the new modifications in the system. 

The question is: should i think about probable blocking the lines by the three way valves?

Normally a two-positions-valve does not block the line. May i think of fail block?

Purposely I want to use these type of valves to avoid any failure to block the lines by operators.  

Edited by Jalalirad, 10 July 2020 - 06:09 AM.

#5 Chemitofreak


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Posted 12 July 2020 - 01:51 AM

What is the type of pump in your service, I guess it will be a positive displacement pump.


The relief valve protecting the discharge piping should be as close as possible to the pump and there should not be any valve in between.


If the fluid is fouling, I would consider the possibility of a blocked outlet, but based on your diagram the relief valve would be of no use in this scenario, because the 3-way valve is at the the upstream of the relief valve, in case the 3 way valve blockage is considered then the piping between the pump and the 3-way valve will overpressurise during a blocked outlet scenario.

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