Converts holo-ACP to apo-ACP by hydrolytic cleavage of the phosphopantetheine prosthetic group from ACP. H2O + holo-[ACP] = (R)-4'-phosphopantetheine + apo-[ACP] + H(+) Belongs to the AcpH family. Could be the product of a pseudogene. The N-terminus is shorter than in related proteins.