I am building a custom car based on a range rover, I will use the standard valve block for the suspension but I am going to use a touch screen PLC to drive it, and control lots of other things.
Here's my problem, Paulp38a suggests that the feeds to the connector on the driver unit are 12v to operate the solenoids, and indeed I have done this during testing with no apparent problem. However other sites suggest that this is a multiplexed signal which changes once the valve is open, and warn of the dire consequences of maintaining 12v (of course non of the valves should be operating for an extended period, the longest is probably a couple of minutes on the diaphragm solenoid whilst the reservoir pressurizes) .
Can anyone categorically confirm or deny this. If it has to have some special signal I can probably generate it but I need to know what it is.

The corner valves are pulsed by the driver pack on a signal from the ECU. Full voltage to open then voltage is reduced to hold and reduced again to give a soft close over a fraction of a second. This clicking continues until the height sensor tells the ECU that either the corner has lifted or fallen as required. Diaphragm solenoid is powered by compressor circuit and and not driver pack, is on whilst compressor runs and off when compressor is off. Exhaust and inlet solenoids have much weaker springs so are held open, whilst height adjustments are made. Each dependent on direction of travel of suspension required. No lowering height adjustments are possible whilst compressor runs.

Why not re-use the suspension ECU as well. Should be quite easy to create the required inputs. Page-25 in "EAS System Info" doc shows all the required inputs.

Wammers - do you know what voltage they consider to be holding voltage. I don't think the soft close is strictly necessary as industrial solenoids don't have that. I could probably arrange for a lower holding voltage if that were strictly necessary. As I have the valve block located in the boot rather than the engine bay, I don't think overheating should be a problem. I haven't noticed anything getting warm during testing.

pwood999- I am interlocking the door switches to my height control to drop to access height and operate my pneumatic side steps. My touch screen plc gives me constant read out of height and much better diagnostics. It also gives me better control over height without the complexity of normal RR control system.

Ideally you should use both the Valve Block and Driver Pack. This way your PLC can simply use 12V / 0V to Open & Close the valves without fear of damage to the solenoid coils. The regular EAS ECU is simply 12V outputs. As Wammers said the ECU pulses the driver pack until the height is correct. The pulses are to avoid too much overshoot in the height changes.

btw, The 12V on-off is exactly what I do in my Manual Control Box, which uses 12V via the push-buttons.

Here's what the driver pack actually does based on ECU input:

Thanks that's perfect