304SS 2.5" 0-5,000 PSI/ 0-350 Bar Liquid Filled Pressure Gauge, 1/4 NPT Bottom Connection

Liquid fill does both. It dampens needle movement caused by vibration and pressure spikes, which makes readings easier to catch at a glance and also reduces wear on the internal mechanism over time. That said, if your system runs with regular pulsation, keep the operating pressure at or below 50% of the full-scale range. On this gauge that works out to 2,500 PSI max under pulsating conditions. Running above that in a pulsating system will shorten the gauge's life regardless of the fill.