A paint circulating system 10 and a pressure relief module 40 utilised therein are described. The paint circulating system 10 comprises a pressurised paint supply pipeline 22, a tank return pipeline 34 and a pressure relief module 40. The pressure relief module 40 comprises: a first flow chamber 65 through which pressurised paint is provided to said supply pipeline 22; a second flow chamber 69 through which paint returns to said tank return pipeline 34; an orifice 42 interconnecting said first and second flow chambers; and a valve member 46 biased towards the orifice so as to block said orifice. The valve member 46 is moveable in response to a pressure in said first flow chamber 65 exceeding a predetermined relief pressure so as to displace said valve member 46 to open said orifice 42. This allows paint to flow from said first flow chamber 65 into said second flow chamber 69, preventing failure occurring in the paint circulating system 10.