The clues are:-
23a.A printing machine, an exercise in which a barbell is elevated ovverhead, a juice extractor, or a clamped device for preserving flowers (5)
28d, TYpe of man-made waterway nnavigable by barge or narrowboat (5)
53d.Word linking with 'wear' for jumpers,hats,scarves,cardigans and other woolen items collectively.(4)
54d.Author remembered for children's novels including Stig of The Dump (4)