Instrument Connections

Instrument connections on different sized pipe.
Temperature Instruments:
- Temperature Instruments come in two basic types, "Insert or Probe type" and "external Contact type"
- Insert Type - These all require a "Temperature Well or Thermo-Well" (TW) that is inserted into the pipe line. The tip or end of the TW should be in the center 1/3 of the line where the temperature of the fluid is not degraded or effected by the outside temperature on the wall of the pipe. The actual Temperature Instrument (TI, TT or other) is inserted into the TW. The Well causes a slight obstruction to the natural flow of the commodity in the line but that is an accepted trade-off to obtain the required reading. The Temperature instrument is inserted into the well.
- TI stands for "Temperature Indicator" - This is just a dial thermometer with a prob that fits in the TW. A TI is normally a local instrument.
- TG stands for "Temperature Gauge" and is just another name for TI. It is not normally used and is not a normal ISA (Instrument Society of America) standard.
- TT stands for :"Temperature Transmitter - This is normally not a "local" read-out instrument. A TT is electronic connected to other items to control some part of the process.

Contact type Temperature just clip or strap on to the outside of the pipe. These are sometimes necessary do to the commodity but are not as reliable or accurate as the probe type.

Line size requirements for TW installation:
There is only limited restrictions on minimum line size for the installation of a TW. You could not put a TW in the side of a 1" line because it would poke out the other side of the pipe. For the length of insertion of a TW study this www.thermowells.com/thermowellspagemain.html go to the "Products" button. It would also block most of the flow path for the commodity. So when the line size is too small then increase the line size for a short distance (1'-0" +/-). This can be done with two Swedge Nipples (Concentric in vertical lines or Eccentric in horizontal lines to allow for free drainage).
Remember only the tip end (1" +/-) of the TW (and the inserted probe) needs to be in the center of the pipe line. To do this you can use a straight-in "O-Let" fitting or an angled (Lateral O-Let) fitting to place the "Tip" where it needs to be. For most larger pipe sizes you just use a straight-in method.

The actual attachment to the side of a line should be in accordance with the Line Class "Branch Table" and the same as for any other branch. For low pressure/low temperature Thread-O-Lets are the best. For systems where Socket-weld connections are required I would use Flanged Wells in a size appropriate flanged end Socket-Weld or Butt-Weld branch.

Pressure Instruments are all externally attached instruments. Pressure Instruments include:
- PI stands for Pressure Indicator (or Pressure Gauge) This is a local instrument and provides direct read-out
- PT stands for Pressure Transmitter. This is normally not a "local" read-out instrument. A PT is electronic connected to other items to control some part of the process.

Pressure Instruments do have some connection related advisories. Locate all PI connections as follows: - 1) Do not locate so sediment can plug in the instrument. 2) Do not locate close downstream of a TW. 3) Place any Pressure connection upstream of any projection into the line or far enough downstream so that turbulence does not influence the pressure reading.

You wrote:
"I am now in a modeling project. The problem I am facing is I have to attach a pressure gauge & a temperature gauge in a pump discharge line. The vertical distance is only 100 mm (4") between reducer and the valve. Do they need any upstream and downstream length? In the horizontal side it is hardly 1500mm (59.5"). In that section I want to fix tg and a branch connection of 50nb (2"). My parent pipe size is 250nb (10")."

Yes I cleaned up some of your grammar and spelling.

1. "I am now in a modeling project. The problem I am facing is I have to attach a pressure gauge & a temperature gauge in a pump discharge line. The vertical distance is only 100 mm (4") between reducer and the valve. Do they need any upstream and downstream length?
No, you do not need any upstream or downstream runs for Pressure or Temperature connections. This is normally true on centrifugal pump discharge lines if the flow is running smooth. However, if you have a Positive Displacement pump you may want a pulsation dampener on the pressure gauge.

2. In the horizontal side it is hardly 1500mm (59.5"). In that section I want to fix tg and a branch connection of 50nb (2"). My parent pipe size is 250nb (10")."
I do not understand these:
- What "horizontal side"?
- What do you mean by "fix"?
- What does "tg" mean?
- Which "parent pipe size"? (the pump discharge in question #1 or something in question #2?)

No!