A pressure balance unit for a valve assembly includes a first shell having a tongue extending therefrom, a second shell having a groove indented therein, and a sliding element having a shaft defining an axis. The groove in the second shell is configured to receive the tongue from the first shell for aligning the shells. The first and second shells are united using a sonic welding process. The first shell defines a first bore and the second shell defines a second bore. The first and second bores include inlet ports in circumferential faces thereof, the ports defining openings transverse to the axis. The sliding element includes a first end movable along the axis within the first bore and a second end movable along the axis within the second bore. The ends of the sliding element open and close the inlet ports by sliding across the ports.