This vacuum valve is designed to protect your spectrometer from oil contamination and damage during a loss of power. When incoming power is lost to the instrument, usually due to a storm or unexpected maintenance issue, the vacuum level at the pump becomes less than at the spectrometer. Without the necessary protection, this pressure difference causes the oil in the pump to be sucked out and deposited in the spectrometer, damaging delicate optics. Although many vacuum pumps have a built in back flow check valve, these are cheap seals hidden inside that fail over time - with out you knowing it! Don't find out the hard way during the next power outage. This is cheap insurance compared to the downtime and expense of a service call to repair oil contamination damage.