Why does the diameter of the impulse piping between a pressure source and a detector have an effect on the rate at which a pressure change is detected?
I know that impulse piping should be as small as possible (without clogging) but why? Why not use 2" diameter piping for a pressure transmitter, assuming cost is not an issue? How does ID affect sensor response time for both a liquid and a gas?
Any amplifying information or links from the technically-minded dopers would be appreciated.
I’ll take a whack at this. It’s because fluid is compressible.
Let’s take it to an extreme. Assume you used a tube 40 feet across and 500 feet long. To raise the pressure inside that tube, you need to compress all the fluid inside, which means you have to pump fluid into the tube. The large the tube, the longer you have to wait until it’s all pumped up to the higher pressure=delay in your response.
I was gonna do a calculation using the bulk modulus of hydraulic fluid as an example, but my little calculator overflowed trying to calculate the volume of that big pipe in cubic inches. 
I thought this was going to be about someone telling Sherlock that he didn’t have to get a big calabash at the checkout lane, because he didn’t have to compensate for anything.
Cost.
2 inch pipe cost a lot more than 1/4 or 1/8 inch pipe.
Check the Jefferies tubes for blockage.
Probably much more important in gases than liquids- gases are very compressible, liquids are usually thought of as “mostly incompressible”.
Additionally, another issue is maintenence - pressure sensors often have to be removed periodically for calibration. You don’t really want to have to loosen a 2" fitting in order to remove your sensor. Not only is this more time consuming to do, but (assuming liquids here), once the fitting is off, you’re going to be losing quite a lot of fluid before you can get a cap back on it.