Description Description Haskel 55828 relief valve set to 4000 PSI. Regulating relief valves were originally developed in response to the need for accurate regulation of high pressure at low flow without the chatter often encountered with valves of this size. They are differential area poppet design with a high ratio between seal and seat area for smooth control, repeatability and low deadband between crack and reseat pressure. State of California Proposition 65 WARNINGCancer and Reproductive Harm - www.P65Warnings.ca.gov. Literature & Docs Accessories