Pressure Transmitter Tapping Point

"Will it be acceptable if instrument was installed above the tapping point..."

followed by:

"company standard states that the instrument should be below the tapping point."

follow the standard, it was written for a reason...

I agree with RVZ717.

You'd need an authorization to deviate from company standards. Before installation.

I would be interested to know their rationale. Some things come to mind:

If the PT is much above or below the tap, the vertical difference will affect the reading, which can be corrected for. This correction will be more difficult if the PT is above the tap, because part of the connecting pipe/tube will contain air. On the other hand, tapping off the bottom of the main pipe may allow debris to collect, blocking the connection to the PT. Just can't win, can we?

For liquids tap should be on side. Bottom tap will cause sludge to settle in impulse piping as pointed out by others.

The drawings at my post #4 are just schematic sketches, for detailed sectional drawing for that instrument connections, I recommend to see and read my post #7.

Our liquid lines are filled with liquids with no entrained gasses so we are not concerned with gasses in the sense lines. Therefore we place our instrument taps for liquid filled lines in the upper 1/3 of the liquid line. This is to ensure that there is no debris to clog the sense line. The instrument can be above the tap point if the total head in the liquid line is high enough to ensure positive pressure at the instrument. However, calibration will have be adjusted for the configuration. In short every instrument installation needs to be designed by a qualified I&C engineer with experience in the system being monitored and instruments being applied. Blind adherence to "standards" and "cookbook" design without an understanding of the system and instrumentation being applied is a guaranteed recipe for failure and a non, or poorly working design.

You are correct, not understanding what it is you are designing is not smart practice, and can be quite dangerous.

However, not conforming to the rules, and standards which are currently in place is a great way to loose your job, find yourself in the gun-sights of a hungry lawyer, or worse. If you see something wrong with a standard, you must take the correct steps to change the standard for the better. If you can prove that something in the standard needs modification, or is wrong, present it to whomever is responsible for it, and suggest (in good taste) what it can be changed to. In today's world, you can't simply "Cowboy up" anymore and really get things done, Far too much red tape surrounds everything.

• Our liquid lines are filled with liquids with no entrained gasses so we are not concerned with gasses in the sense lines.

No experienced engineer can say like that, because any liquid line is subjected to locate some traces of gases or vapour (from liquid itself) or may be a pockets of air entrapped into the liquid piping.

• Blind adherence to "standards" and "cookbook" design without an understanding of the system and instrumentation being applied is a guaranteed recipe for failure and a non, or poorly working design.

Very great words from unknown person with unknown experience, to the extent we don't know his name/nickname. In addition, we didn't find any reason for him to say like that.

• ABC piping design for a Junior piping engineer to clearly understanding of my schematic (just schematic) sketch of orifice flanges at my post #4, where the detailed drawing of the instrument connections is accomplished by staggered connections with 90^o to facilitate assembly and disassembly of instrument fittings and valves. And these detailed drawings may be cleared through the isometric drawings, or through a standard drawings, or specifications for the whole project.

• In addition, in case of liquid connections, the staggered connections help avoiding collection of debris and deposits and intern avoiding clogging the tubes and instrument fittings.

• The prescribed good practices was experienced and applied for a lot of hundreds projects designs in piping systems for more than 30 years ago.

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The general rule is exactly what Mr. Abdel says about gas and liquid services. Materials such as pulp that are a cross of solids, liquids with a little gas thrown in as well as restricting physical situations may require special attention for the installation of some instruments. You should follow the manufacturers recommendations always because they probability done the research to know how it works best. If you have a special situation ask them or your vendoer if in your circumstance if it would be ok to mount it different. I have seen and done this before many times in the past when installing something that just would not go any other way. They will probably tell you 1 of three things:

1 fine and you can keep the warranty,

2 it doesn't really mater except it may not last as long and you will lose your warranty

3 no you cannot because it won't work that way and you fail if you tdo it

Once you get your answer you will have to decide if mounting it against the manufacturer's recommendations is worth it. Many times I have seen it be worth it in my situations as long as it fell in the 1 or 2 catagoies above. It is always best to know what the man that built or sold it thought before you decide to mount an instrument or really do anything different than recommended.

The tap(s) need to be at or below the pipe centerline. Good practice is at 45 deg below. The instrument "should" also be mounted below for reasons already explained in previous comments. You are stuck with the floor, but the way around the problem is to use a diaphragm seal. You can then mount the transmitter in any configuration....

We had 2 pumps discharging cold water to a common pipe to supply AHU systems. A pressure transmitter (Px) is install on top of the horizontal pipe before entering the common pipe. For some reasons, the reading of the pressure transmitter was not noticed since commissioning of the system. But the reading of the local pressure gauge (Pg) mounted on vertical pipe just after the discharge of the pump showing 8 bar was often refered. The pressure trans is not the diffential pressure type, just a tapping point)

Recently, reference was made on Px and notice that it reads between 0 to 1 bar. The questionable Px was replaced with new and calibrated pressure transmitter and the Px reading remain at 0 to 1 bar from the trend plot.

Question: As I am away from the instrument trade for some good no of years, but I remember from my training that Pressure transmitter tapping (take off point) should be taken from the side of the pipe, like what you guys are talking about. Is what we experience due to tapping installation ?

It is probable that you have entrained compressibles in the transmitter impulse line and body when a liquid application is taken from the top of pipe. Suggest side mount at 45 deg down to allow for a full liquid leg.