Arag Manual Pressure Relief Valve with Flange Fittings.  Rated for 20 Bar pressure, bypasses liquid to ensure that the maximum line pressure is not exceeded.  Body made from fibre-glass reinforced nylon, spring is 303 stainless steel and gasket material is viton.  Bypass port has 1" BSP Male thread.  Also has 1/4" BSP Female threaded port for optional pressure gauge.