laid out the cable to valves box – about 40m distance, managed to shorten it. Using 3 x HV100 valves and 1 x DV100. They all work without any water pressure, but they all also buzz like they are going to blow up. Some tremble too while active and buzzing, others just buzz. I think OS even turns them off at times and will not run them for a full minute as I request. Pulled the meter and read 21.6 VAC :-0 – on HVs. DV came out at 20.8 VAC.
Next I have connected two wires together for one valve in order to halve the impedance (one-way, the return wire was not doubled) and read 22.3 VAC- but still the buzz was there. Took out that solenoid and tested it straight at OS outlets. These HV100 valves seem to be a little noisier than humming, but still, I managed to get rid of its buzzing by firmly pressing its wires against OS outlet screws (not so firm /wonky contact resulted in same buzz). There also is another valve box closer to the OS outlets and those valves inside hum, not buzz. I am thinking about attempting with a 30 VAC transformer. Other ideas ?