Instead of regulators at each machine what about a pressure relief valve on the main line. When only a few machines are operating the relief valves just dumps the excess flow back into the main tank.
If you do want regulators and it is water mixed coolant I suggest the regulators that are used for domestic water supply. These mey not be appropriate for straight oil because the diaphragm and seals may not handle oil; actually they may not handle coolant.
An open mind is a virtue...so long as all the common sense has not leaked out.