Application

Pressure switches are electromechanical devices that are activated by pressure and deactivated by pressure. The pressure point that activates a pressure switch is called the set point, while the pressure threshold that deactivates a pressure switch is called the cut-out point.

The adjustable pressure switches are used in control systems, where at the project level it is necessary or convenient to obtain a change of state for a specific pressure value. For example, in domestic heating systems, the opening of a tap in the domestic water circuit produces lower pressure and consequent activation of the boiler. Or, in air conditioning systems for motor vehicles, a high-pressure switch activates the condenser fan when a certain operating pressure value in the system is exceeded (deactivates compressor if a critical value is exceeded), and a low-pressure switch deactivates the compressor in case of inadequate suction pressure (determined, for example, by an insufficient amount of refrigerant fluid quantity, too low ambient temperature or operating defect of the interior ventilation system).

Other common applications of pressure switches are in safety systems, hydraulic and pneumatic brake systems, convoy vehicles, trains or air compressors.

Controls and switches for pressure: Available Functions

We present you with a wide selection of pressure switches, gauges, and instruments. Our products are certified according to the PED directive with features like blockage prevention and intrinsic safety. Nippon’s devices can be used in gas, flue gas, water, oil, and any other liquid-filled environment. The types of switches we offer are fixed or adjustable differential, as well as manual restart and reset devices with many different types of membranes. These allow for use in autoclave systems, boilers, and compressors, as well as any low or high pressure system that utilizes an IP65 rating.

Pressure Switches Models

There are three types of pressure transmitters: absolute, gauge, and differential.

Pressure at absolute zero

We refer to vacuum pressure as 0 psi (a). Atmospheric pressure is usually 14.7 psi (a).

Pressure gauge

Gauge pressure is the total pressure minus atmospheric pressure, which is commonly used to measure pressure.

Please note that 0 psi (g) is the atmospheric pressure.

Pressure differential

There is a difference in pressure (or differential pressure). Pressure is the force acting vertically on a unit area.

Models Available

The management of technical processes in any field of activity, such as in the manufacturing or automotive industry, requires control of the pressure of the fluids that operate the system. This requires associating a particular pressure value, which is important for the system, to an electrical signal, for instance, to run a machine cycle or indicate particular applications (leaks, alarms, etc).

These operations can be controlled using a kind of pressure sensor, set to suit particular applications. See Pressure Switches.

PRINCIPLE OF OPERATING PRESSURE SWITCHES

Set screws are used to calibrate pressure switches so that they can function correctly. A calibration spring determines the load of the switch by acting on the set screw. In order for the electrical contact to close or open when the pressure setting has been reached, the spring opposes the thrust of the fluid, exerting pressure on the sensitive element (a membrane or piston).

From an electrical point of view, there are three main types of pressure switches:

• With normally open (NO) electrical contacts (SPST)
• Two-way normally closed (NC) electrical contacts (SPST)
• Three-way changeover electrical contacts (SPDT)

NORMALLY OPEN PRESSURE SWITCHES

The NORMALLY OPEN contact is open, i.e. there is no flow current.

The electrical contact closes when the pressure setting is reached.

NORMALLY CLOSED (NC) PRESSURE SWITCHES

The NORMALLY CLOSED contact is closed when the pressure is applied. We can see that the contacts are closed and the signal is present on the external contacts. When the pressure setting is reached, the electrical contact rises and interrupts the signal.

SWITCHING CONTACTS FOR PRESSURE SWITCHES (SPDT)

Using the SWITCHING CONTACTS version a micro switch is activated when pressure is applied to the fluid on the separated element (diaphragm or piston). In this version, we can choose between NC and NO contacts, or both, depending on the application (but not both).