Pressure Gauges and Hydrotesting

I have not always seen two guages used, but there absolutely is a static pressure differential between ANY vertically separated guages installed in a hydronic system.

The weight of water will generate a 1.0 PSIG differential every 2.43 feet of vertical separation, assuming the the fluid is water. With other fluids, the differential will be the density divided by 2.43 for each PSIG of pressure differential.

The use of two guages may be solely because the tank / vessel is not expected to be completely full of liquid during "normal" operation and one pressure guage is for static (gaseous) pressure and the other is for the dynamic (with some level of static head) pressure.

Obviously, any tank of vessel that is designed to be "dry" when operating would onlyu display the static pressure of the gaseous contents during operation.

A correction to one of my comments- it was lat at night and I got a little fuzzy.

If the liquid is not water, the pressure will be 2.43 DIVIDED BY THE DENSITY for each PSIG delta. Example- if the liquid has a density of 1.2, the required distance of vertical separation for 1 PSIG will be about 2 feet. A density of 0.8 sill require about 3 feet of separation.

thank you for the answer, but I like to put here a clarification of my question. while hydrotesting,the vessel will be filled full of water/liquid(static pressure exists,guage pressure zero)and if we apply pressure further by means of a pump, will the pressure adjust to be uniform throughout the liquid regardless of location?

Water is a hydraulic medium. The rise in pressure will be uniform throughout the vessel and any piping connected to it. However, any static pressure will still be observed.

A1) Possibly because the witness test protocol requires it.

A2) Certainly. The difference in pressure will be related to the static headof the test fluid between the two <...pressure gauges...>; the one closer to the centre of the Earth will read higher, either because of the laws of gravity or because the Earth sucks.