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Old August 12th, 2017, 05:21 AM   #1
shkoko2000
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Wet leg and dry leg

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?"
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Old August 12th, 2017, 09:24 AM   #2
RussB
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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
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Old August 12th, 2017, 09:40 AM   #3
shkoko2000
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Mainly i need to know use dry or wet leg
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Old August 12th, 2017, 09:52 AM   #4
Bit_Bucket_07
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Here is an AutomationWiki link: http://automationwiki.com/index.php?...el_Measurement
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Old August 12th, 2017, 10:14 AM   #5
shkoko2000
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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
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Old August 12th, 2017, 12:57 PM   #6
keithkyll
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Sensing liquid. You don't care about the gas. Use Wet leg.
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Old August 12th, 2017, 01:19 PM   #7
ganutenator
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If she owns a dog, it most likely wet leg.
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Old August 12th, 2017, 02:54 PM   #8
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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.
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Old August 13th, 2017, 11:23 AM   #9
boneless
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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.
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Old August 13th, 2017, 11:46 AM   #10
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Something to read..

http://www.instrumentationtoolbox.co...#axzz4pedlpnjh

https://www.google.com/search?rlz=1C...k1.yU8LrRz9APY
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Old August 13th, 2017, 12:20 PM   #11
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Quote:
Originally Posted by g.mccormick View Post
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.
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Old August 13th, 2017, 01:52 PM   #12
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Quote:
Originally Posted by Bit_Bucket_07 View Post
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.
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Old August 13th, 2017, 02:59 PM   #13
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Quote:
Originally Posted by g.mccormick View Post
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.
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Old August 13th, 2017, 03:35 PM   #14
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Quote:
Originally Posted by Bit_Bucket_07 View Post
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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Old August 13th, 2017, 03:59 PM   #15
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Quote:
Originally Posted by g.mccormick View Post
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)
The transmitter will require calibration whether it is set up with a wet leg or a dry leg on the low side.
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