Superconducting diodes have attracted considerable interest for nonreciprocal device applications owing to their dissipationless transport. Here, we theoretically propose that a tunnel junction based on the Kekulé graphene superlattice can host a finite valley supercurrent that exhibits pronounced nonreciprocity even in the absence of superconductivity, giving rise to a dissipationless valley diode effect. This effect originates from the additional reflection phase acquired by electrons in each transverse channel and supports perfect valley diode rectification with 100% efficiency, which can be readily tuned via the gate voltage. This finding provides a platform for designing dissipationless valleytronics in a more versatile manner.