F1 Engines _ Valve technology
All F1 engines have used pneumatic valves for some time, first introduced by Renault on the late versions of the their V6 turbo engine.

Wire spring valve

Previously wire valve springs have been used, they use a coil spring (13) to return the valve (1) to a closed position after the cam has retarded. They required huge amounts of the detail development on their shape and material to reach the rev limits of around 15k RPM. The pressure to deliver power from 3.5l and later 3.0l engines required ever higher rev ceilings and metal springs could not longer be developed at the same rate as the rest of the engine.

Pneumatic valve spring

Pneumatic systems use conventional cams operating the valve (4) via a shim\bucket or finger follower, the valve spring pocket is replaced with a chamber (28) pressurised with nitrogen (held within a cylinder in the sidepods) that runs at a constant pressure to return the valve when the cam timing retards. You often see the teams suffer a loss of pressure in the races through leaks in the system, the driver comes in and mechanics re-pressurises the pneumatic circuit, this rarely works for more than few laps. Also when Engines are changed the un-installed engine needs a remote gas cylinder connected in order for the valves not to drop and hit the pistons.

Wire spring vs Pneumatic valve comparision

Renault Electro-Hydraulic (Camless) valve actuation

Renault have not planned an Electro-mechanical system, which was commonly believed to use actively controlled magnetic coils to open and close the valves. Clearly the electrical and RPM performance required from the this system were not ready or suitable for a F1 engine.
What Renault have is an Electro-hydraulic system, where two pressurised circuits operate the valve (16). Valve return is still handled by the pneumatic system (52, 20), but the opening of the valves discards cams for a hydraulic circuit (50) controlled by a electronic valve (58). As this system can use high pressure hydraulics already on the car to operate the valve at the required RPM ceiling, the system seems almost too simple..! Infinitely variable valve timing plus the loss of the reciprocating weight of the cams and drive gears makes this an enticing solution. This solution has yet to race or to my knowledge even be tested in a car, Renault have admitted that as a broader automotive organisation, that this systems has been tried.