Crusader

[iggymiggy]

18d ancient architect to tip home over(7) i???t?p
19d fellow takes pressure with neat form of anaesthetic(7) h???a?e
23a hydrogen and copper sent by a river to railway truck(9) ????e?c?r

[dannyk13]

18d.Imhotep

[mac44]

19d. heptane

[dannyk13]

19d.Heptane

[gangesboy]

23 buffetcar

[maggiebee]

23a coalesce?

[gangesboy]

sorry ignore my post - should be hoppercar

[iggymiggy]

23a the letters i now have are h?p?e?c?r

[gangesboy]

anag of H (hydrogen) and copper + a r(iver)

[gangesboy]

hoppercar

[iggymiggy]

thanks

[netherfield]

Honestly 23a should be (6,3), can't find anywhere where it's one word.