Circulation unit, liquid discharge head, and liquid discharge apparatus

Abstract

A circulation unit includes first and second pressure adjusters, each including a valve chamber, a pressure control chamber, a communication port providing communication therebetween, a valve configured to open and to close the communication port, a flexible member, and a pressure plate. The valve is opened when in its pressure control chamber is lower than PX, or closed otherwise. The pressure plate and the valve of the second pressure adjuster are in a contact state when pressure in its pressure control chamber is lower than PY, or in a non-contact state otherwise. Here, PX and PY satisfy PX−PY<|ΔP| (upper limit value≥zero, with which the pressure plate and the valve of the second pressure adjuster switch to a contact state before a differential pressure between the pressure control chambers reaches that necessary for starting printing after operation of a circulation pump being stopped is resumed).