Modular control valves are normally mounted onto a valve skid with piping at the rear, or underneath, to allow quick changes to be made for maintenance purposes. Piping can, however, be dispensed with almost totally by mounting valves onto a manifold block- with interconnections formed by drilled passages in a solid block or by cut-outs on a plate-formed manifold.

Modular valve assemblies allow piping to be reduced still further. These follow standards laid down by the Comit~ European des Transmission Oleophydrauliques et Pneumatiques and are consequently known as CETOP modular valves.

Modular valves consist of a base plate and a wide variety of modules which may be stacked up on top. At the top of the stack a spool valve or crossover plate is fitted. Quite complicated assemblies can be built up with minimal piping and the ease of a child’s building block model.