The use of external, suction inlet control valve appliances is wide spread in the fire service. These valves do a nice job of allowing the control of water intake, bleeding air from LDH supply lines, and providing over-pressurization protection on the supply hose side of the valve. In most all cases, the relief valve feature of these appliances is NOT easily adjustable on the emergency scene and therefore must be set at a known pressure before the appliance is put on the pump's suction inlet.
In some cases, purchasers just put the suction inlet control valves on their pumps without verifying the relief valve setting. This practice will likely result in a problem sooner or later - especially if the relief valve is set low. For example, the brand new, external suction inlet control valve shown in these photos was put on the pumper and the relief valve ended up being set at the lowest possible pressure setting (50 psi) - so this proved problematic from the start at this water supply drill when another pumper had to pump to this pumper.
Therefore, best practice is to know (and verify) the pressure setting of the relief valve on your external suction inlet control valve - and, that pressure should represent the test pressure of your supply hose since that is what the device is meant to protect. Annual hose testing time is a good time to verify these settings.