There are different types of valves that perform different tasks in plants and require appropriate approvals and tests.
Safety valves are safety equipment in accordance with Directive 2014/68/EU, Pressure Equipment Directive. As the last link in a series of safety measures, they prevent the plant component from bursting due to an impermissibly high pressure. They are set to the desired response pressure, marked accordingly and sealed. A later change of the setting pressure is only possible in experienced workshops. The set pressure of all safety valves is checked before delivery, if required also in the presence of an inspection company. A safety valve must pass an EU type examination and, if necessary, a TÜV component test before it can be sold in series.
Pressure relief valves fulfil the same function as safety valves. However, they have no safety function and are therefore not classified as safety equipment but only as pressure equipment according to the Pressure Equipment Directive. No special examination is necessary. As a rule, they have a proportional opening characteristic. Pressure relief valves do not achieve the performance of safety valves and can be delivered adjusted, marked and sealed, but do not have to be.
The set pressure within the spring range can be adjusted by the plant operator as required in the case of overflow/control valves. They perform a "pressure control task" in the system. As this is not a safety-relevant function, overflow/regulating valves are only classified as pressure-maintaining equipment according to the Pressure Equipment Directive. No special examination is necessary. These valves have a proportional opening characteristic in order to avoid pressure surges in the system. Overflow valves must always be gas-tight.
Pressure reducing valves require a component approval for building services engineering if they are used for drinking water installations. Their task is to reduce the pressure in a part of the plant. While with pressure relief valves the presence of an excessively high pressure on the inlet side and therefore a flow through the valve is the exception, with pressure reducing valves a higher applied pressure on the inlet side is the rule. They are continuously flowed through and ensure a uniform fluid flow with constant, reduced pressure on the outlet side even with fluctuating pressure on the inlet side (e.g. after a pump).