Wet leg and dry leg

shkoko2000

Member
Join Date
May 2011
Location
cairo
Posts
296
Dear all,
Good day,
Please i need your help as i have a condensate surge vessel and mounted on it two level transmitter(DP type).one for (HH and H alarm that make pump operating) and the other one for (L and LL alarm to make the pump stop). This vessel is containing condensate and above it blanket gas. My question is" what is the configuration of the two transmitter dry or wet leg?"
 
It depends.
~ is there a controller** that the two sensors are inputs to?
~ if not do the controllers have any "intelligence"?
~ is each alarm type a separate dry contact or solid state switxh?

** more information may be needed
 
I know the difference between them but i need to know condensate surge vessel used wet or dry leg from experience or from best practice
 
I would think that you want the high or wet leg on the bottom port, then the lo or dry leg on the top port.
 
I guess that would depend on your medium.

We measure level in hot water and steam boilers. Here both sides of the DP measurement will have water. The lower measures the actual level, the higher will fill up with condensate and be the reference point.
 
I would think that you want the high or wet leg on the bottom port, then the lo or dry leg on the top port.

In an open vessel, the low side of the DP transmitter may be open to atmosphere.

In a closed vessel, the low leg should be connected to the top port in the tank.

If the gasses that accumulate in the top of the vessel will condense and introduce fluid into the low side piping, then you must fill the piping with fluid and recalibrate the DP transmitter for "wet leg" operation. Otherwise, the fluid that accumulates in the low leg piping will create head pressure on the transmitter which introduces a measurement error.
 
In an open vessel, the low side of the DP transmitter may be open to atmosphere.

In a closed vessel, the low leg should be connected to the top port in the tank.

If the gasses that accumulate in the top of the vessel will condense and introduce fluid into the low side piping, then you must fill the piping with fluid and recalibrate the DP transmitter for "wet leg" operation. Otherwise, the fluid that accumulates in the low leg piping will create head pressure on the transmitter which introduces a measurement error.


Another option would be a condensate trap that is drained.
 
That strikes me as a more complex solution than simply using a wet leg on both sides of the transmitter. I'm a fan of the KISS Principle myself.

True. The only thing is that you would not have to rezero and span the transmitter (or figure out scaling taking into account specific gravity etc)
 

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