Forklift Relief Valve -Full internal type relief valve. Supplied with 3/4″ MNPT inlet connection. Starts to discharge pressure is 375 psig. Enough capacity for DOT 33-1/2 lb. and 43-1/2 lb. lift truck cylinders. Pamphlet 58 2001 edition requires that lift truck relief valves must be replaced 12 years after date of manufacture of the cylinder and every 5 years thereafter.