HydraulicPneumatic Gauges Hydraulic and Pneumatic Pressure Gauges are rugged, low-cost pressure gauges for hydraulic and pneumatic applications. DME offers low prices and quick shipment. Liquid fill helps dampen pulsations and acts as a natural lubricant. Generally, gauges should be selected so the maximum working pressure is not in excess of 75% of full scale range. Hydraulic: 2-1/2" diameter. Melt Pressure GaugeRigid and Flexible Stems. All stainless steel construction. Requires no electrical power-maintenance free.