How do I measure and monitor pressure in my process system?

Measuring process pressure starts with choosing between local indication and remote monitoring. A pressure gauge gives you a visual reading right at the point of measurement — ideal for operator rounds, maintenance checks, and quick local verification. If the pressure data needs to go to a PLC, DCS, or SCADA system for trending, alarming, or closed-loop control, you need a pressure transmitter that converts the measurement into a standard 4–20 mA or digital signal. Many installations use both — a gauge for local visibility and a transmitter for the control system. Pressure switches provide a discrete on/off output when pressure crosses a set threshold, used for high-pressure alarms and safety shutdowns. For corrosive, viscous, or high-temperature media that would damage a standard sensor, a diaphragm seal isolates the instrument with a flexible membrane and fill fluid. Accessories like snubbers (to dampen pulsation from pumps and compressors) and siphons (to protect gauges from live steam) extend instrument life and improve accuracy in challenging conditions.

What is the difference between a pressure gauge and a pressure transmitter?

A pressure gauge is a local, visual indicator — it displays the current pressure on a dial or digital screen at the point where it is installed. Gauges are used for operator rounds, maintenance checks, and local process verification. They do not send a signal to the control system. A pressure transmitter converts the measured pressure into a standard electrical signal (typically 4–20 mA) that is sent to a PLC, DCS, or SCADA system for monitoring, trending, alarming, and control. Transmitters enable remote pressure monitoring and closed-loop pressure control without requiring an operator to be physically present at the gauge. Many installations include both — a gauge for local visual indication and a transmitter for remote monitoring and control. When selecting between them, consider whether the pressure data needs to be available only locally (gauge) or integrated into the plant control system (transmitter, or both).

What is a diaphragm seal and when is it needed?

A diaphragm seal (also called a chemical seal or remote seal) is a flexible membrane that isolates the pressure-sensing element of a gauge or transmitter from direct contact with the process media. The space between the diaphragm and the instrument is filled with a compatible fill fluid (typically silicone oil or fluorinated fluid) that transmits the process pressure to the instrument's sensing element hydraulically. Diaphragm seals are needed when the process media would damage, clog, or contaminate a standard instrument — corrosive chemicals, viscous fluids, slurries, hot media that would damage the sensor, sanitary/food-grade applications requiring cleanable surfaces, or media that solidify or crystallize in instrument cavities. They are also used when the process temperature exceeds the instrument's rating — the diaphragm seal acts as a thermal barrier. Seals are available in a wide range of materials (316SS, Hastelloy, tantalum, PTFE-lined) and mounting configurations (direct mount, remote mount with capillary tubing).

How do I select the correct pressure gauge range for my application?

The gauge range should be selected so that the normal operating pressure falls in the middle third of the dial — between 25% and 75% of the full-scale range. This ensures accurate reading under normal conditions while providing headroom for pressure spikes without pegging the pointer. For example, if the normal operating pressure is 60 psi, a gauge with a range of 0–100 psi or 0–150 psi is appropriate — not 0–60 psi (too close to full scale, no headroom) or 0–300 psi (operating point is in the bottom 20% of the scale, reducing readability). ASME B40.100 recommends that the maximum operating pressure not exceed 75% of the gauge's full-scale range for steady pressure service, and 65% for fluctuating pressure service. Also consider the gauge's accuracy class, dial size (larger dials for better readability), connection size and type (NPT, socket weld), case material, wetted material compatibility, and whether a liquid-filled case is needed for vibration damping.

What are pressure gauge snubbers and siphons, and when are they needed?

Snubbers and siphons are protective accessories installed between the process and the pressure gauge to extend gauge life and accuracy. A snubber (also called a pulsation dampener or restrictor) contains a small orifice or porous element that restricts the flow of media into the gauge, damping out rapid pressure pulsations from pumps, compressors, or reciprocating equipment. Without a snubber, the gauge pointer oscillates rapidly, making reading impossible and wearing out the gauge mechanism prematurely. A siphon (pigtail siphon) is a U-shaped or coiled tube installed between a steam line and the gauge — it traps a column of condensed water that prevents live steam from reaching the gauge's Bourdon tube. Steam temperature would damage the gauge's internal mechanism; the water column transmits the pressure while keeping the gauge at a safe temperature. Use a snubber whenever the process pressure pulsates or fluctuates rapidly, and use a siphon whenever measuring steam or high-temperature vapors.

Pressure Control - Tescom Anderson Greenwood

Pressure control products measure, monitor and regulate pressure in liquids, gases and steam. Accurate pressure control protects equipment and keeps processes stable.

Pressure Control Products

Categories from Tescom Anderson Greenwood (3)

Manifold Valves

Instrument manifold valves mount between process piping and pressure or differential pressure transmitters. A manifold lets technicians isolate, equalize, vent and calibrate instruments without shutting down the process.

Manifold Types

2-valve manifolds – isolate and vent gauge and pressure transmitters
3-valve manifolds – isolate and equalize DP transmitters
5-valve manifolds – add vent and calibration ports for DP service
Direct-mount and remote-mount – fit your transmitter installation
Stainless and alloy bodies – for corrosive and high-pressure service

Choosing a Manifold

Match the manifold to the transmitter type and connection (flanged or NPT), and the process pressure and temperature. Choose hard or soft seats according to temperature and leak-tightness requirements. Integrated manifolds save space and leak points.

Centro supplies instrument manifold valves for pressure and DP transmitter installations.

Related categories: Pressure Control Accessories | Gauge Cock Valve | Pressure Snubber | Instrument Valve | Syphons

Instrument Valve

Instrument valves isolate, vent and control flow to gauges, transmitters and analyzers. They give technicians safe access for maintenance and calibration.

Instrument Valve Types

Needle valves – precise flow control and isolation
Ball valves – quick quarter-turn shutoff
Block and bleed valves – isolate and vent in one body
Gauge valves – compact isolation for gauges
Check and relief valves – protect instrument lines

Choosing an Instrument Valve

Match pressure and temperature ratings, materials and connections. Choose seat materials for the media and temperature.

Centro supplies instrument valves for instrumentation and sampling.

Instrument Valve Accessories

Instrument valve accessories complete instrument installations with handles, mounting brackets, plugs, caps and fittings that keep valves secure and serviceable.

Accessories Available

Replacement handles – standard and color-coded
Mounting brackets – panel and pipe mounting
Plugs and caps – seal unused ports
Locking devices – prevent unauthorized operation
Fittings and adapters – connect tubing and pipe

Choosing Accessories

Match accessories to your valve series and connection types. Color-coded handles help identify functions.

Centro supplies instrument valve accessories.

Related categories: Pressure Control Accessories | PT Plugs | Syphons | Instrument Valve | Gauge Cock Valve

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