Apeiron

Will air in the capillary tube of a mechanical oil pressure gauge affect its reading?

Vader

Fe Primate,

In theory, no. Pressure exerted on the gauge by any fluid, either gas (air) or liquid (oil) will casue the bourdon tube to deflect the same amount, and indicate the same reading. The air may act as a cushion, however, and make the gauge a bit less responsive, but the sustained pressure will eventually read correctly.

It's very similar to the air in a well water tank, glycol filled tires, or the air in your radiator. There is the same pressure exerted on the air as the liquid, so any gauge connected to it would indicate the pressure of both. The oil pressure gauge doesn't require a hydrostatic columm to operate, but would likely be a bit faster without entrapped air.

Apeiron

Yeah that's what I thought. Trying to figure out which gauge I'm supposed to believe.