Fuel pressure gauge question

[pearljam724]

Why do some fuel pressure gauges have a liquid in them ? I assume it’s oil ? Is there any advantage of a gauge having this liquid or not ? I assume it’s for the purpose of preventing the needle from bouncing back and forth too fast. You know, to slow the needle down. But, i’m not sure and always wondered about that.

 

[67Dart273]

Liquid is normally used to dampen pulses, such as from a mechanical pump. Since the gauge must be sealed, the might also help to keep out dust / dirt etc. One disadvantage is that some liquid filled gauges are more prone to outside changes, such as barometric or temperature