Measuring Gas Pipe Pressure

you may needa 2 stage pressure regulating system. A high pressure regulator valve at the main line takeoff and a low pressure regulator near the burner

You mean, to measure pressure in main line, don;t you?

IF so just use Tee or reducer that will fit to your pressure gauge. The size of them don't affect to pressure value.

Maybe you should check the capacity of your regulator, with 2" lines you are driving a big burner I guess and have undersized the regulator ?? or have a very long pipe run the fact that the pilot manages to drop the pressure that much would indicate the latter.

Failing these a 2 stage regulation system would be the easy fix.

Can you please assist me on pressure regulation. What is the difference between pressure control and flow control. Is it that feedback for the controller in flow control is Flow and presure in pressure regulation only. Can shed light in terms of velocity , pressure and flow in both cases

Whoops am sorry I misread your original post I thought you said pressure drops by 3.8KPa not to 3.8KPa big difference!!

That is not to excessive however you should be reading the pressure on the main line close to the burner not 30mt away due to friction in the line the pressure will be less at the burner when it is operating.

The burner has a jet with hole of a size which is calibrated to give the best performance for which it was designed , it requires the gas to be at a certain pressure to give the correct volume of gas to be burnt. The regulator maintains this pressure due to its own design and if the gas line is of the correct size it will maintain close to the required pressure at the burner jet.

Flow Control Instrumentation (FCI) has a great web site with loads of information on this subject and they offer excellent equipment which can accurately measure both pressure and flow.

Pressure is a measurement the force that causes a reaction/movement to occur whereas flow is a measurement of the quantity of medium (gas,liquid,solid) moving (flowing) in the container past a given/established point for a length of time.

The quantity of flow is a result of the pressure applied, ambient temperature, the viscosity/density (specific gravity) of the medium, the volume/size of the container conveying the medium, the quantity and size of restrictions throughout the conveying container, the temperature of the medium being conveyed, the superexpansibility of the medium, and the quantity of moisture in the medium.

Basically if the pressure is dropping below acceptable design limits during operation you do not have the proper "upstream" pressure, the piping is too small, there are too many restrictions (reducers, elbows, contaminants, orfice-plates,etc.) and/or "all of the mentioned" to maintain your system flow demand requirements.

There are many companies that will analyze your system and recommend a "fix" for no-cost if you are in the market for instrumentation or other controls.

Be careful and cautious as gas pressure/flow below design requirements can result in the combustion (fireball) moving/traveling back into the burner and/or the piping and resulting in an explosion. If you are not absolutely sure, get professional help even if you have to pay for it.

The Southern California Meter Association as well as other organizations offer a great handbook full of formulas and other information pertinent to measuring many different types of materials.