Bypasses excess liquid. Adjustable to maintain control of any line pressure within the valve operating range. Selected pressure setting firmly held in place by locknut. Extra large valve passages to handle large flows. Excellent chemical resistance. 1/4" Port for pressure gauge pipe plug included. Model 23120 features 302 stainless steel spring and EPDM O-ring. Model 23120A features 316SS spring and Vitron O-ring. All Valves 150 psi (10 bar) except 23120-PP-60-VI 60 psi (4 bar).