US Patent 9714534 Door closer

A hydraulic door closer is disclosed. The hydraulic door closer may include a top cap surrounded by an O-ring that is located at the top of the hydraulic door closer housing opposite a spindle to seal the hydraulic fluid within the housing. In addition to or in lieu of the top cap design, the door closer may include a locking washer to secure the valves to the housing; epoxy and an O-ring at the interface between the top cap and the housing of the door closer; use of a dual-walled rubber seal around the spindle; use of dual O-rings on each valve stems; use of caps that are made of the same material as the housing instead of aluminum and use of epoxy on the end caps; and/or use of backcheck with an adjustable spring.