Back-pressure and pressure-relief valves are fittings for dosing systems Depending on the task involved, they are used to increase the dosing accuracy or to protect the system against excess pressure. If the delivery pressure is higher than the dosing pressure, dosing without a back-pressure valve is not possible. With the dosing of fluids, back-pressure valves generate a defined back pressure on the pressure side of a dosing pump. This is required in the following cases: • Strongly fluctuating pressure. Exact dosing results are impossible without a back-pressure valve. • The pressure on the suction side is higher than on the pressure side. • Dosing in a pressureless line is required. Pressure relief valves have an important safety function for protecting the dosing pump and the associated pipes and fittings. The dosing pump can generate a pressure that is many times the rated one. Various reasons, e.g. soiling or operating errors can result in blocked pressure lines. At an appropriate pressure, a pressure relief valve opens a bypass line and protects the system in this way from damage caused by over-pressure. A shutoff valve (A) enables the dosing system to separate the non-return valve from the pressurized system. The shutoff valve enables the maintenance of the non-return valve after separation from the system and should be closed before longer down times because the leak-free nature of the non-return valve could be restricted through soiling particles or wear.