Tony will underquote anyone, as long as they're outside his area!
Er, problem:
If your mains is that high pressure you really need to take the shower cold supply from the outlet side of the pressure reducing valve on the unvented inlet, so H and C pressures are the same.
This probably means a new pipe into the house from the garage, probably a nightmare. A reasonable workaround would be a pressure reducing valve at the shower, or a pressure equallising valve if you get a good one. Cheapies restrict the flow rather a lot.
Where's the discharge pipe going to go, by the way?
Er, problem:
If your mains is that high pressure you really need to take the shower cold supply from the outlet side of the pressure reducing valve on the unvented inlet, so H and C pressures are the same.
This probably means a new pipe into the house from the garage, probably a nightmare. A reasonable workaround would be a pressure reducing valve at the shower, or a pressure equallising valve if you get a good one. Cheapies restrict the flow rather a lot.
Where's the discharge pipe going to go, by the way?