Frequently asked questions

Here you will find answers to questions which we are often asked.

In case you have a special questions please contact us. We will be pleased to help you and give you our advice.


Definition of a safety valve according to DIN EN ISO 4126-1
A safety valve is a valve which automatically, without the assistance of any energy other than that of the fluid concerned, discharges a quantity of the fluid so as to prevent a predetermined safe pressure beeing exceeded, and which is designed to reclose and prevent further flow of fluid after normal pressure conditions of service have been restored.

Safety valves

  • Certified valves with TÜV / PED and/or CE Type Test Approval
  • Normal lift- Full lift opening / closing characteristic
  • Higher blow-off capacities than pressure relief valves

Pressure relief valves

  • Valve without certification/approval (without safety function according to PED)
  • Proportional opening- / closing characteristic
  • Lower blow-off capacities than safety valves

Whether a plant operator is allowed to use a pressure relief valve, or if he must usa a certified safety valve depends primarily on the type of application or plant. Both valve types are intended to be the last safety device in a system. In the case of systems or plants requiring official approval or which fall under the European Pressure Equipment Directive (PED), the valve must hold corresponding approvals and certifications.

The function of a safety valve is based on a simple balance of forces between the force of the pressure spring and that of the medium.

In the closed position, which is the normal position of the valve when installed on the plant, the spring force is greater than the force of the medium and the valve seals the plant tight. In case the set pressure of the valve is exceeded due to an increase in the plant pressure, the valve opens to relieve the excess pressure by blowing-off the medium.

After excess pressure in the plant has been relieved below the closing pressure, the valve closes completely.

An overflow valve is a valve with proportional control characteristics for pressure maintenance, pressure control and for protecting pumps or plant systems against excessive pressures.

Yes, the customer himself can do the setting of an overflow valve within the given spring range.

Depending on the series, the pressure can be adjusted by means of an open-ended spanner, a hex key or by hand wheel.

An overflow valve has a proportional opening characteristic, i.e. the more the pressure of the medium rises, the more the overflow valve opens in order to discharge the required output.

No, an overflow valve is not intended to be the last safety device of a plant. In an installation, an overflow valve carries out a control function.

Goetze overflow valves with metal bellows can compensate back pressure up to a maximum of 4 bar, therefore there is no impact on the set pressure. Overflow valves without bellows however are not back pressure compensated.

  • Back pressure compensation up to a maximum of 4 bar.
  • Protection of sliding parts for applications with sticky or highly viscous media.

A pressure reducing valve (or pressure reducer) is a valve fitted in a pipe system, which in spite of varying pressures on the inlet side (inlet pressure) makes sure that a certain pressure on the outlet side (outlet pressure) is not exceeded, thus protecting the components and equipment on the outlet side.

In the case of a pressure reducing valve, the outlet pressure (pressure prevailing on the outlet side) is set. The set pressure of a pressure reducing valve always refers to the outlet pressure at zero usage. i.e. no medium is flowing through the valve and all draw-off points are closed.

If a draw-off point on the outlet side is opened medium flows through the valve and the outlet pressure falls below the set pressure. Once the draw-off point is re-closed the outlet pressure rises again to the set pressure.

For most pressure reducing valve series valve inserts or repair kits are available. Further information including part numbers are to be found in the technical datasheets.

Pressure gauges are available as separate accessories

The pressure reducing valve controls the outlet pressure – the inlet pressure has no influence on the control of the pressure.

Yes, the outlet pressure can be adjusted within the spring range by means of standard tools or an adjustment handle.

No, the pressure regulation is always based on the static pressure at zero usage of the medium.

No, the pressure reducing valves are described as "fully balanced", this means that varying inlet pressures are compensated by means of the geometry of the valve and thus have no influence on the outlet pressure.

Sealing materials

Seals are there to ensure the tightness of components. But why are there so many of them? The answer is quite simple: The suitable sealing material depends on the medium, the temperature and/or the pressure under which the valve has to operate and guarantee safety. Some of the sealing materials are barely resistant against chemical products, while others prove the opposite and can also withstand extreme temperatures and high pressures.

Learn more about the most important sealing material in use at Goetze:

NBR has good resistance to media like hydraulic oils, mineral oils, mineral oil products, oil in water emulsions, water glycols, animal as well as vegetable oils and petrol. NBR has good mechanical properties making it a versatile sealant. Depending on the type of use the temperature range is 30 °C to +130 °C.

FPM has excellent resistance to high temperatures, oxygen, mineral oils, synthetic hydraulic fluids, fuels, aromatics, many organic solvents and chemicals. Although for water and steam the temperature limit is approx. +60 °C. Additionally, the low permeability to gas allows the use in high-vacuum applications. FPM is often a substitute material for NBR. Depending on the type of use the temperature range is -20 °C to +200 °C. Certain mixtures achieve values between -40 °C to +230 °C. For the use with oxygen, BAM tested materials are in use (BAM= “Bundesanstalt für Materialprüfung”, German institute for material testing).

EPDM has good resistance to oxygen, diluted acids and many chemicals; however it is not applicable with mineral oils. With hot water and steam in closed circuits, temperatures up to 180 °C are possible. EPDM is often used in connection with foodstuffs (Manufacturer authorization according to FDA and elastomer guideline). Depending on the type of use the temperature range is -40 °C to +170 °C. For the use with oxygen, BAM tested materials are in use (BAM= “Bundesanstalt für Materialprüfung”, German institute for material testing).

FFKM is a high performance elastomer with a similar high chemical resistance as PTFE. In addition, it has elastic properties. It is used mainly in applications for O-ring seals in the chemical industry, as well as the food industry with FDA approval. In addition, FFKM is resistant against steam. Depending on the type of use the temperature range is -10 °C to +260 °C.

Generally, PTFE has an excellent chemical resistance. For the use with oxygen, BAM tested materials are in use. (BAM= “Bundesanstalt für Materialprüfung”, German institute for material testing). As sealing material it is only used in modified versions. Special advantages are the reduction of permeation and cold flow. Depending on the type of use the temperature range is -200 °C to +225 °C.

By admixing carbon, significantly higher tensile strength values are achieved. In comparison to modified PTFE, this material is particularly more suitable with higher pressure loads and has a similar chemical resistance. Depending on the type of use the temperature range is -200 °C to +225 °C.

In the case of metal to metal sealing, various materials can be used depending on the application. Special advantages are high temperature ranges and the same chemical resistance as the material of the valve body. Depending on the type of use the temperature range is -270 °C to +400 °C.