There is Differential pressure (DP)

[Sandeepuch]

There is Differential pressure (DP) type level tranmitter to measure level inside the column. There is flushing oil (FLO) connection in both the lower and upper tapings of DP type level. This is because the fluid inside the column is tend to choke the tapings for level measurement, so to avoid this flushing connection provided. A typical drawing attached for your visulatization where blue color represent liquid inside the column. Ideally DP type transmitter should measure the difference in P1 and P2 (As per image). But due to FLO flow in both the upper taping and lower taping it will measure different pressure at both the tapings i.e. P4-P3. What should be the flow of FLO in both the tapings such that it will measure the actual level inside the column. RO valve provided for flow regulation of FLO in both the tapings. what will be the flow so that P1=P3 and P2=P4 OR P2-P1=P4-P3. Consider the concept of entry loss

 

[Compositepro]

The purpose of the flow indicators is, first to insure you have flow to keep the lines flushed, and second to be able to adjust each flow rate so the pressure drop in each sensing line is equal. With equal pressure drops, the dP reading is unaffected by the the pressure drops. There are also dedicated flow controllers available for this purpose. They include a needle valve, rotameter, and pressure regulator, all in one, to keep the flush flow constant.

 

[IRstuff]

Homework problemsshould be posted in the Student Engineer forum

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[georgeverghese]

For services such as this, industry practice is use diaphragm sealed impulse lines leading to LT.

 

[pierreick]

Hi,
Consider this link:

https://www.brooksinstrument.com/en...-lines-of-a-differential-pressure-transmitter

Other technologies are better suited for your application, let say Radar.
Pierre

 

[Sandeepuch]

I thought at upper taping there should not be any entry loss so P1=P3 whatever the flow of FLO. This is because if FLO flows from a pipe falls into a COLUMN (or whatever), the diameter of the FLO stream after the exit does not change, its velocity does not change, there is no turbulence outside the pipe-exit, and there is no entry loss. Am i correct?
Similarly at Lower taping there will be exit loss of 0.5v2/2g and dynamic pressure conversion to static pressure will cancel out the loss. So there should be P2=P4, Irrespective of FLO flow. Am I correct?

 

[LittleInch]

There is entry loss at the higher tapping point,. It does not remain a pipe ID sized column of liquid dies it?

Entry loss is entry loss. The static head is what makes P4 higher than P3.