Pressure switch

Q: What is a pressure switch?

A pressure switch is an electromechanical device that detects a specific pressure level in a system and closes or opens an electrical circuit when that threshold is reached. It converts a physical pressure input into an electrical output, allowing control systems to start or stop pumps, alarms, compressors, or valves. Pressure switches come in various forms, including diaphragm pressure switches, piston pressure switches, and differential pressure switches, and are used across HVAC, water systems, hydraulic and pneumatic applications, and industrial automation. Key sensing elements include diaphragms or pistons that deflect under pressure Output configurations commonly include SPST (on/off) and SPDT (changeover) contacts These devices can be adjustable or fixed-setpoint, depending on the model

Q: How does a pressure switch work and what types exist?

At its core, a pressure switch uses a sensing element (often a diaphragm or a piston) that responds to fluid or air pressure. When the pressure reaches the preset setpoint, a mechanical movement drives a contact to open or close, completing or breaking an electrical circuit. There are several common types: Diaphragm pressure switches: Flexible membrane transduces pressure into a displacement that triggers the switch. They are well suited for clean liquids and gases and offer compact, corrosion-resistant options. Piston pressure switches: A rigid piston translates pressure into movement, enabling robust operation in higher pressure ranges and rugged environments. Differential pressure switches: Monitor the difference between two pressures (P1 and P2) to detect filter loading, flow changes, or filter clogging in HVAC and filtration systems. Typical contact configurations include SPST-NO, SPST-NC, and SPDT, with adjustable or fixed setpoints. Some models provide multiple setpoints, hysteresis control, and electrical ratings suitable for AC or DC circuits.

Q: How do I choose a pressure switch for my application?

Selecting the right pressure switch involves matching the device to your operating environment, media, and electrical requirements. Consider the following factors: Ensure the switch operates within your system’s minimum and maximum pressures, with an adjustable range if future variations are expected. Choose materials (brass, stainless steel, wetted parts) compatible with air, water, oil, refrigerants, or corrosive fluids. Pick thread types (G, NPT, BSP) and port sizes that match your piping or tubing. Determine voltage, current, and whether you need SPST, SPDT, normally open, or normally closed contacts. Consider IP ratings, temperature range, and enclosure styles for flameproof, washdown, or dusty environments. Decide on diaphragm versus piston designs, and materials like brass or stainless steel based on corrosion resistance and mechanical life. Look for certifications (UL, CE, ATEX, IECEx) relevant to your industry. A good practice is to map your system’s required response time, hysteresis (the gap between cut-in and cut-out pressures), and the need for adjustments to select a model that minimizes nuisance alarms and ensures reliable operation.

Q: What are differential pressure switches and where are they used?

Differential pressure switches monitor the difference between two pressure points rather than a single pressure. They are widely used to: Measure filter condition in air and liquid filtration systems Control fan speed or pump operation in HVAC and water processing Detect clogged nozzles, blocked vents, or flow restrictions in industrial processes These switches aid proactive maintenance by triggering alarms or controlling equipment when the pressure drop exceeds a preset threshold, helping avoid system inefficiency or damage. The sensing elements can be diaphragm-based or piston-based, and outputs can be SPST or SPDT with adjustable setpoints.

Q: What are common materials, connections, and installation considerations for pressure switches?

Common materials include brass bodies with stainless-steel wetted parts for corrosion resistance in water and chemical environments, and stainless steel or high-grade alloys for high-pressure or high-temperature service. Port connections often use G1/4, 1/4" NPT, or M20 threads, with compatibility to pipe fittings and quick-connect tubing. Choose material compatibility with the system fluid to avoid degradation or leakage Verify port thread size and installation orientation to prevent backflow and ensure accurate sensing Use proper mounting hardware and consider vibration isolation to extend life Protect electrical connections from moisture and contaminants; employ appropriate enclosures for safety Proper calibration and periodic maintenance help maintain accuracy. Where necessary, differential measurements should be revalidated after installation changes or fluid property shifts.

Q: What are typical electrical configurations and how do I wire a pressure switch?

Most pressure switches provide simple control outputs compatible with industrial controllers and relays: SPST-NO: Close the circuit when the setpoint is reached; opens when below setpoint SPST-NC: Open the circuit at setpoint; closes when below setpoint SPDT: Common terminal with a normally open and a normally closed contact, offering a changeover output When wiring, ensure the supply voltage matches the switch rating, use appropriate fusing, and observe safety precautions. If the load draws significant current, use a suitable relay or contactor to handle the load safely, and consider wiring in a control circuit with proper isolation and protection.

Q: What related products should I consider with pressure switches?

For comprehensive system control and monitoring, RS Components offers a range of related devices: Pressure transducers and pressure sensors for precise measurement and digital interfacing Flow switches and differential pressure transmitters for monitoring flow and pressure dynamics Solenoid valves and pneumatic cylinders to actuate controlled responses based on pressure Pumps, regulators, and filters to maintain stable pressure conditions Gauges and test equipment for calibration and verification Wiring, enclosures, and mounting hardware to complete safe, reliable installations By pairing a pressure switch with compatible transmitters, regulators, and control components, you can design robust automation and safety systems across HVAC, industrial, and process industries.

Q: How do I install and maintain a pressure switch safely?

Safe installation and maintenance extend the life of a pressure switch and improve system reliability: Power off and depressurize the system before installation or servicing Check for compatibility with media, temperature, and environmental conditions Mount the switch in an orientation that aligns with the sensing element’s design and avoids vibration hotspots Ensure correct electrical connections and proper strain relief for cables Conduct a leak test after installation and verify setpoints and hysteresis Periodically inspect for corrosion, residue buildup, or mechanical wear, and recalibrate if necessary If the system uses hazardous fluids or high pressure, follow relevant safety standards and use approved accessories to maintain integrity and safety.

Pressure Reading Type

Absolute, Gauge (135)

Differential (98)

Relative (80)

Gauge (36)

Relative, Vaccum (5)

Absolute (4)

Residual, Vacuum (1)

Control Button/Switch Colour

Black (100)

Red (47)

Blue (34)

Green (16)

White (10)

Grey (3)

Black, Green, Red (1)

Black, Green, Red, Yellow (1)

Chrome (1)

Number of Ports

3 (66)

2 (50)

5 (29)

3/2 (25)

5/2 (13)

1 (5)

4/2 (4)

4 (1)

Thread Standard

G (88)

BSPP (29)

R (15)

Rc (12)

BSPT (11)

Metric (7)

ISO 7 (6)

Push In (4)

NPT (3)

Response Time

≤2 ms (89)

<1.5 (Minimum Switching Output) ms, <3 (Maximum Analogue Output) ms (22)

<3 (Minimum Switching Output) ms (18)

5 ms (13)

≤3 ms (10)

≤10 (Analogue) ms, ≤5 (Discrete) ms (6)

10 ms (6)

4 ms (1)

Analogue Output

4 → 20 mA (78)

0 → 10 V, 4 → 20 mA (22)

0.5 → 4.5 V (17)

0 → 10 V (16)

1 → 10 V (1)

Number of Positions

2 (108)

3 (22)

1 (2)

"Pressure switch"

RS PRO Pressure Switch, G1/8 -1bar to 15 bar

RS PRO Pressure Switch, G1/8 -1bar to 3 bar

RS PRO Pressure Switch, G1/4 0bar to 420 bar

RS PRO Pressure Switch, G1/4 -1bar to 80 bar

RS PRO Pressure Switch, G1/4 1bar to 16bar

RS PRO Digital Hydraulic Pressure Switch, R 1/8 in 0.1kPa to 0.1 → 1 kPa

RS PRO Digital Hydraulic Pressure Switch, R 1/8 in 0.1kPa to 0 → 101 kPa

RS PRO Pressure Switch, G1/4 -1bar to 80 bar

RS PRO Pressure Switch, M12 x 1 1bar to 16bar

RS PRO Pressure Switch, NPT 1/4 0.2bar to 4 bar

RS PRO Pressure Switch, M12 x 1 1bar to 16bar

RS PRO Pressure Switch, M12 x 1 1bar to 30 bar

RS PRO Pressure Switch, M12 x 1 0.5bar to 8bar

RS PRO Pressure Switch, G 1/4 20bar to 400bar

RS PRO Pressure Switch, M12 x 1 0.5bar to 8bar

RS PRO Pressure Switch, M12 x 1 0.2bar to 2 bar

RS PRO Pressure Switch, G 1/4 5bar to 50bar

RS PRO Pressure Switch, G 1/4 10bar to 100 bar

RS PRO Pressure Switch, G 1/4 10bar to 100 bar

RS PRO Pressure Switch, G 1/4 30bar to 250 bar

RS PRO Pressure Switch, G 1/4 0.2bar to 2.5 bar

RS PRO Pressure Switch, G 1/4 1bar to 12 bar

RS PRO Pressure Switch, G 1/4 1bar to 10bar

RS PRO Pressure Switch, G 1/4 5bar to 50bar

What is a pressure switch?

How does a pressure switch work and what types exist?

How do I choose a pressure switch for my application?

What are differential pressure switches and where are they used?

What are common materials, connections, and installation considerations for pressure switches?

What are typical electrical configurations and how do I wire a pressure switch?

What related products should I consider with pressure switches?

How do I install and maintain a pressure switch safely?