Pressure switches

A pressure switch is a pressure sensor, which switches an electrical contact (open or close) when fluid pressure reaches a set threshold.

Therefore, reaching the preset pressure is converted into an on/off electrical signal, which can be used for instance to trigger alarms, indicate leaks or start machines.

Pressure switches are frequently used in several industries, and are often considered as safety devices of pressure systems.

Mechanical pressure switches

A mechanical pressure switch works without any power supply, being the electrical contacts potential-free.

The fluid pressure enters into the sensor and generates a force on the separating element (diaphragm or piston). This force counteracts the pre-tensioned spring. When the pressure force is greater than the spring force, the internal mechanism moves and switches the electrical contact. The electrical contact will switch back when pressure force is reduced below the hysteresis value.

How to adjust a mechanical pressure switch

Pressure switches are defined by their pressure range, in which the switching pressure can be adjusted.

The switching pressure (also known as switching point or set point) is adjusted by rotating the screw placed on the top of the pressure switch. By rotating clockwise the switching pressure is increased, by rotating anticlockwise the switching pressured is decreased.

Due to the hysteresis, when adjusting the switching point, we need to consider if system pressure will be increasing (rising ramp) or decreasing (falling ramp).

Hysteresis of a pressure switch

The hysteresis is the difference between the switching point when pressure is rising, and the switching-back point when pressure is falling. The hysteresis of a mechanical pressure switch is a function of its design and structural layout. The hysteresis has no constant value, and increases with increasing switching point.
In some pressure switches, hysteresis can be adjusted at factory in the range of 10 to 30% of switching point value.

Diaphragm and sealing materials in a pressure switch

Diaphragm and sealing materials in a pressure switch will depend on the fluid type (media), which is being used.

Pressure switches with NBR diaphragm and seals

NBR (Buna-N) is the standard material most commonly used. It is suitable for most types of hydraulic oils, mineral oils, heating oils, air, nitrogen, etc. Its temperature resistance goes from -40°C to +100°C.

Pressure switch for hydraulic oil (mineral oil)

Pressure switches in zinc-plated steel, with NBR diaphragm and seals are suitable for most standard mineral oils and hydraulic oils. Please choose you pressure switch for oil here.

Pressure switch for compressed air

Pressure switches in zinc-plated steel, with NBR diaphragm and seals are suitable for compressed air and nitrogen. Please choose you pressure switch for air here.

Pressure switches with HNBR diaphragm and seals

HNBR is a special material optimized for ester-based bio oils. It is also suitable for many types of mineral oils and synthetic oils. Its temperature resistance goes from -30°C to +120°C.

Pressure switches with EPDM diaphragm and seals

EPDM is particularly suitable for applications with process water, oxygen, hydrogen, ozone, acetylene, brake fluid, etc. Its temperature resistance goes from -30°C to +120°C.

Important note: EPDM must not come into contact with oils because this would entail swelling and softening of the material, and so failure of the pressure switch.

Pressure switch for water

In addition to the EPDM, it is recommended to use pressure switches in stainless steel, to protect them against corrosion. Please choose you pressure switch for water (process water) here.

Pressure switch for oxygen

In addition to the EPDM, it is recommended to use pressure switches in stainless steel, being the maximum working pressure of 50 bar. Pressure switches need to be delivered completely free of oil and grease to prevent spontaneous combustion. Hence Plasma cleaning is highly recommended to guarantee the elimination of any oil and grease. Please consult us in case you need a pressure switch for oxygen.

Pressure switches with EPDM-TW diaphragm and seals

EPDM-TW is intended for drinking water applications and for use in medical and pharmaceutical applications. Its temperature resistance goes from -20°C to +100°C.

Important note: EPDM-TW must not come into contact with oils because this would entail swelling and softening of the material, and so failure of the pressure switch.

Pressure switch for drinking water

In addition to the EPDM-TW, it is recommended to use pressure switches in stainless steel, to avoid corrosion. It is also suitable to use the SUCO silicone, which is FDA-approved. Please consult us in case you need a pressure switch for drinking water.

Pressure switches with Silicone diaphragm and seals

The SUCO silicone is FDA-approved for the food sector (Food & Drug Administration). Its temperature resistance goes from -40°C to +120°C. Its maximum working pressure is 35 bar.

Important note: Silicone is not suitable for oil applications.

Pressure switch for alimentary fluids

In addition to the SUCO silicone, it is recommended to use pressure switches in stainless steel, to avoid corrosion. Please consult us in case you need a pressure switch for alimentary fluids.

Pressure switches with FKM (Viton) diaphragm and seals

FKM (Viton) exhibits special chemical resistance and has proven to work successfully with critical oils. Its temperature resistance goes from -5°C to +120°C.

Electrical contacts of pressure switches

A pressure switch can have a normally open (NO), normally closed (NC), or changeover (SPDT) electrical contacts.

Rated and maximum voltage and current have to be respected, in accordance to the type of load being powered (utilization category).

It is highly recommended to use an electrical relay to separate the control circuit (where the pressure switch operates), from the power circuit with its bigger loads and currents.

For standard electrical contacts (silver contact) minimum voltage of 10V and minimum current of 10 mA are needed to counter the build-up of impurity layers on the electrical contacts. Above these minimum values, mechanical friction and electrical erosion ensure the electrical continuity of the contact.

For lower voltages and currents pressure switches with gold contacts are highly recommended to ensure electrical continuity.

Responsibility in selection of pressure switches

The specifications on medium compatibility cannot be generalized as they pertain to the diaphragm and sealing materials used by the manufacturer. The information cannot be used for all application scenarios.

Testing the suitability of a SUCO pressure switch for a specific application rests under the responsibility of the user. It may be the case that suitability can only be verified with appropriate field-testing.

Suco pressure switches

Suco pressure switches are manufactured in Germany according to highest quality standards. Suco pressure switches are designed for the most challenging applications, providing exceptional reliability and durability. Please choose your Suco pressure switch with the filters offered in this website.