Questions on DP Transmitter Wet Leg Compensating Impulse Line

Calculate the appropriate LRV and URV pressures for this hydrostatic level measurement system.

Assuming the process liquid has a weight density of 44 pounds per cubic foot at a temperature of 23 degrees Celsius, and that the “wet leg” compensating impulse line is filled with a glycerin/water mix (S.G. = 1.13).

Assume a static vessel pressure of 126 PSI:

Questions on DP Transmitter Wet Leg Compensating Impulse Line

Question 1:

Express your answers in units of inches water column (”W.C. or ”H2O).

Answer:

LRV = +173.7 ”H2O

URV = +94.76 ”H2O

The temperature and static pressure values are extraneous information, included for the purpose of challenging students to identify whether or not information is relevant to solving a particular problem.

Question 2:

As liquid level increases in this vessel, will the transmitter’s signal increase or decrease (i.e. is this level transmitter direct or reverse acting?

Question 3:

If the process liquid heats up and becomes less dense (but the actual level remains the same), will the transmitter’s 4-20 mA signal increase, decrease, or remain the same?

Question 4:

If the wet leg is filled with pure glycerin instead of a glycerin/water mixture (but the process liquid level remains the same), will the transmitter’s 4-20 mA signal increase, decrease, or remain the same?

Question 5:

How would this system respond if someone closed the upper nozzle block valve, isolating the compensating leg impulse line from the process vessel?

Question 6:

Describe a step-by-step procedure for re-filling the wet leg with glycerin, assuming a pressurized vessel.

Do you find any mistake in these questions?

Share with us through below comments section.

Credits: Tony Kuphaldt

Share With Your Friends

2 thoughts on “Questions on DP Transmitter Wet Leg Compensating Impulse Line”

  1. Answer2: decrease
    Answer3:remain the same
    Answer4:remain the same
    Answer5: signal is stay constant with last case before close nozzle
    Answer6:
    The column will be affected by the pressure of the tank, whether it is an increase or decrease, and thus the reading of the transmitter will change if there is a change in the liquid level
    All that by imposing a closed air pressure equalization valve

    -I hope I understand the questions well

    best regards

    Reply
  2. How possible the low side of the DP be connected to the bottom of the Process VESSEL.

    Answer for URV and LRV for the above question is not correct , I’ve got (LRV = -206.79” H2O, URV= -128.79 )

    Formula I used

    LRV= Lmin * SGp – (H1+H2) * SGf

    URV= Lmax* SGp – (H1+H2) * SGf

    Reply

Leave a Comment

Questions on DP Transmitter Wet Leg Compensating Impulse Line

Send this to a friend