Browse Pressure Instruments
Pressure gauges
Pressure gauges give a direct reading where the pressure is measured. Because they work independently of your control system, they’re a valuable local check for operators and an important part of engineering risk management.
Analogue pressure gauges
Suitable for: Liquids · Gases · Steam (with a siphon)
Most analogue pressure gauges use a Bourdon tube: a curved, flattened metal tube, usually C-shaped but sometimes helical, sealed at one end. As pressure rises inside the tube, its oval cross-section tries to become round, and the tube starts to straighten. A linkage turns that small movement into the movement of the pointer. Bourdon tube gauges measure gauge pressure and can also be made to measure vacuum. For very low pressures, capsule gauges use two thin diaphragms joined together for greater sensitivity.
Teltherm is the only New Zealand manufacturer of Bourdon tube pressure gauges. Our analogue gauges comply with the accuracy requirements of BS EN 837-1:1998 and NZS/AS 1349:1986, and are available with:
• a stainless steel case with brass or stainless steel internals
• low-pressure capsule versions
• dial sizes of 63 mm, 100 mm and 150 mm, with larger sizes in some cases
• a wide range of process connections
• custom scales.
Digital pressure gauges
Suitable for: Liquids · Gases · Steam (with a siphon)
Digital pressure gauges combine an electronic pressure sensor with a digital display. Like analogue gauges, they usually work on their own, but they offer higher resolution and accuracy, and extra features. They’re used for local indication, portable pressure measurement and data logging, and as reference standards for checking other instruments. We supply digital pressure gauges from global manufacturers.
Pressure transmitters and switches
Where a pressure reading needs to reach a control room, PLC or data logger, or trigger an action, you need a transmitter or a switch.
Pressure transmitters
Suitable for: Liquids · Gases · Steam (with a siphon)
Pressure transmitters are the standard way to measure pressure in a process where you need remote indication or control. The transmitter converts the pressure into a proportional signal that your control and data logging systems can read. Signals can be analogue, such as 4–20 mA or 0–5 V, or digital over a range of industry-standard communication protocols. Transmitters are available for gauge, absolute and differential pressure.
Pressure switches
Suitable for: Liquids · Gases · Steam (with a siphon)
Pressure switches detect a single, preset pressure. When the pressure rises or falls past that point, the switch opens or closes a set of electrical or electronic contacts, which can raise an alarm, start or stop a pump or compressor, or shut down a process.
Pressure sensor technologies
Both analogue and electronic instruments rely on a sensing element that moves or flexes under pressure. Electronic instruments then convert that movement into an electrical signal, and the sensor technology they use affects accuracy, stability and suitability for your application.
Strain gauge sensors
Suitable for: Liquids · Gases · Steam (with a siphon)
Strain gauge sensors have resistive elements bonded or deposited onto a diaphragm. As pressure flexes the diaphragm, the resistance of the elements changes in proportion. Strain gauge sensors are rugged, accurate and stable, and are widely used in industrial transmitters.
Piezoresistive (silicon) sensors
Suitable for: Liquids · Gases · Steam (with a siphon)
Piezoresistive sensors use resistors built into a silicon diaphragm. When pressure deforms the silicon, its electrical resistance changes. These sensors are sensitive and compact, and are common in transmitters and digital gauges. They’re sometimes mistakenly called piezoelectric sensors, which work differently.
Capacitive sensors
Suitable for: Liquids · Gases · Steam (with a siphon)
Capacitive sensors use a diaphragm as one plate of a capacitor. As pressure moves the diaphragm, the gap between the plates changes, and so does the capacitance, which the electronics measure. They can be built for absolute, gauge or differential pressure, and are well suited to low pressures and differential pressure measurement.
Piezoelectric sensors
Suitable for: Liquids · Gases
Piezoelectric sensors use a quartz or ceramic crystal that generates an electrical charge when it is squeezed. They need no external power to produce a signal and respond very quickly, which makes them ideal for rapidly changing pressures, such as pulsations and pressure spikes. They aren’t suited to steady, static pressure, and they can be sensitive to shock and vibration.
Seals, relief valves and test pumps
The right accessories protect your instruments and your process, and let you test instruments where they’re installed.
Diaphragm seals
Suitable for: Liquids (including viscous, corrosive and dirty media) · Gases
A diaphragm seal, also called a chemical seal, is a connection that isolates a pressure gauge, transmitter or switch from the process. A flexible diaphragm sits in contact with the process, and the space behind it is filled with a fill fluid that passes the pressure to the instrument. Seals are used where the process is corrosive, viscous, crystallising, hot or hygienic, or contains solids that would block the instrument’s port. They can be mounted directly on the instrument or connected by a capillary.
Pressure relief valves
Suitable for: Liquids · Gases
Pressure relief valves protect equipment and people by opening automatically at a set pressure, releasing enough fluid to stop the pressure rising further. Once the pressure falls back below the set point, the valve closes again.
Comparison test pumps
Suitable for: Liquids (hydraulic) · Gases (pneumatic)
Comparison test pumps are a pressure source for testing. The pump generates pressure, and the instrument under test is compared with a reference gauge or calibrator connected to the same pump. Hydraulic pumps suit higher pressures; pneumatic pumps suit lower pressures and gas service.
Pressure calibrators and calibration
Pressure instruments drift over time, especially where there is vibration or pulsation. Regular calibration keeps your readings trustworthy.
Pressure calibrators
Suitable for: Liquids (hydraulic) · Gases (pneumatic)
Pressure calibrators are used to calibrate or verify the pressure instruments in your process, in the laboratory or on site, and as commissioning tools. They range from simple indicators to advanced units with manual or automatic, self-stabilising pressure generation, a choice of output signals, and data logging and reporting.
Accredited pressure calibration
Our pressure calibration is accredited by IANZ to ISO/IEC 17025, and we can calibrate in our laboratory or on your site. We can also service and repair many types of instruments. See Instrument Calibration NZ for more.
Choosing the right pressure instrument
Start with what kind of pressure you need to measure.
Gauge, absolute or differential pressure?
• Gauge pressure is measured relative to the surrounding atmospheric pressure. It’s the most common measurement, and it reads zero when the instrument is open to the air.
• Absolute pressure is measured relative to a perfect vacuum, using a sealed vacuum reference inside the instrument. Standard atmospheric pressure at sea level is 1013.25 mbar absolute, but the actual value changes with weather and altitude. That means a gauge reading will shift slightly when the weather changes, even if the absolute pressure in your process doesn’t.
• Differential pressure is the difference between two points in a system, such as either side of a filter, orifice plate or pump.
What we consider
• the process connection details
• the fluid’s properties, and any vibration or pulsation
• the pressure and temperature of the fluid and its surroundings
• your preferred units of measurement and output type
• power, installation and maintenance requirements
• hazardous area, compliance and certification requirements.
Which instrument suits your application?
| Instrument | Liquids | Gases | Steam | Output |
|---|---|---|---|---|
| Analogue pressure gauge | ✓ | ✓ | ✓ (with a siphon) | Local display |
| Digital pressure gauge | ✓ | ✓ | ✓ (with a siphon) | Local display, logging |
| Pressure transmitter | ✓ | ✓ | ✓ (with a siphon) | Continuous signal |
| Pressure switch | ✓ | ✓ | ✓ (with a siphon) | Switch point |
| Diaphragm seal | ✓ | ✓ | – | Connection (protects the instrument) |
| Pressure relief valve | ✓ | ✓ | – | Overpressure protection |
| Comparison test pump | ✓ (hydraulic) | ✓ (pneumatic) | – | Pressure source for testing |
| Pressure calibrator | ✓ (hydraulic) | ✓ (pneumatic) | – | Reference reading |
On steam, instruments are fitted with a siphon, a loop of pipe that fills with condensate, so live steam never reaches the sensing element.
Frequently asked questions (optional)
What’s the difference between gauge and absolute pressure?
Gauge pressure is measured relative to the surrounding atmosphere, so it reads zero when open to air. Absolute pressure is measured relative to a perfect vacuum, so at sea level it reads about 1013 mbar when open to air.
Are your pressure gauges made in New Zealand?
Yes. Teltherm is the only New Zealand manufacturer of Bourdon tube pressure gauges. Our analogue gauges comply with the accuracy requirements of BS EN 837-1:1998 and NZS/AS 1349:1986, and can be supplied with a choice of materials, sizes, process connections and custom scales.
Can I use a pressure gauge on steam?
Yes, with a siphon fitted between the process and the gauge. The siphon fills with condensate, which protects the gauge from the high temperature of live steam.
When should I choose a digital gauge instead of an analogue one?
Choose a digital gauge when you need higher resolution or accuracy, data logging or other extra features, or a reference for checking other instruments. Analogue gauges suit simple local indication and need no power.
What’s the difference between a pressure transmitter and a pressure switch?
A transmitter sends a continuous signal proportional to pressure, for monitoring and control. A switch only changes state at a set pressure, for alarms and on/off control.
How often should pressure instruments be calibrated?
As a general guide, every 12 months, unless your equipment documentation or quality system sets a different interval. Our pressure calibration is IANZ-accredited, in our laboratory or on your site.