Abstract: This invention provides a leak proof seal between a high pressure fluid line and a gauge monitoring the pressure of the fluid in the line. This seal transmits pressure fluctuations between the measured fluid and a dissimilar fluid in the standing line connected to the measuring gauge and prevents the comingling of the two fluids. This invention is particularly applicable in instances where the ambient temperature is below the freezing point of the measured fluid and a non-freezing fluid is required in the standing line and gauge. The gauge protector seal comprises an in-line elastomeric piston and cylinder which passes through variations in the pressure in the measured line to the fluid in the standing line to the gauge while maintaining separation of the two fluids and at the same time allowing the non-freezing fluid in the standing line to lubricate the piston.