The older Bunning and ECE spreaders had only a single relief valve on the bed drive thus extensive damage can be caused if the bed is run the wrong way when the spreader is full. We recommend the fitting of double relief valves especially if you are hiring out.
It is important to set these relief valves correctly. Different sizes of spreader and different sizes of motor may need different pressures. Bunning's recommended pressures for their 2014 Lowlander 120 Mk 4 are 2000 psi for empting and 1000 psi for reverse. These valves can be set prior to fitting by connecting them to a tractor hydraulic output. You will need 2 suitable hydraulic hoses, a T piece, a pressure gauge and a blanking plate.
All items are readily available from us or elsewhere, the blanking plate is easily made, just a flat piece of 8mm or thicker plate with 4 bolt holes drilled in it.
Some models of motor won't accept this relief valve. There are numerous valves available but what we do is put one of the same valves in the line, however the motor side of the valve has no threads in the ports, so a suitable adaptor plate will need to be fabricated. We could do this for you or you could do your own, it is not difficult, see the pic below.
We accept no responsibility for any loss or damage caused by following this advice.