Company Profile

Inline Flow Sensors: Compact In-Line Fluid Presence and Speed Sinks for Equipment

Quick Answer: Silver Instruments supplies compact inline flow sensors for equipment OEMs, skid builders, and process plants that need fluid presence detection and speed output in DN10 to DN50 lines. These sensors transmit 4-20 mA, pulse, or switch signals to a PLC, pump interlock, or valve controller. Send your pipe size, fluid type, pressure, temperature, and flow range to receive a fixed quotation from our team.

Most engineers look for inline flow sensors when a full flow meter is too large, too costly, or unnecessary for the control loop. We have seen this on customer sites many times. A food plant in Vietnam uses a DN20 inline sensor to confirm CIP return flow before the next wash step. A pump package builder in Chile uses a DN15 speed sensor to detect diesel flow to a burner. Both applications needed a compact device with no bypass line.

Some equipment drawings use the term speed sinks for the pulse or frequency input channel on a controller. In practice, the flow sensor sends a speed signal. The controller input accepts that signal. That is why the phrase appears in OEM specifications. Silver Instruments treats the sensor as the source and the PLC or motor drive as the receiving device.

What an Inline Flow Sensor Does

An inline flow sensor sits directly in the fluid stream. It detects fluid presence, flow speed, or both depending on the model. A flow switch gives a simple on or off signal. A speed sensor gives a frequency or analog output that represents flow velocity. Both outputs are common in equipment control panels.

Here is the thing. A pump interlock only needs to know if liquid is moving. A flow switch with a 24 V DC supply can shut down the pump in under one second. A dosing skid may need more detail. A speed sensor with a pulse output can tell the PLC how fast the fluid moves and confirm that a metering pump is actually dosing.

Common pipe sizes for inline sensors are DN10, DN15, DN20, DN25, and DN50. Standard process connections include NPT, BSP, and tri-clamp. For water and light chemicals, NPT is often the cheapest option. For food and beverage lines, tri-clamp is the preferred connection because it allows quick removal for cleaning.

Sensor Types and Fluid Matching

Silver Instruments offers three main inline flow sensor technologies. Paddle wheel sensors work well in clean water and light chemicals up to 80 °C. They provide a pulse output that is easy to read on a PLC. Thermal dispersion sensors work for oil, coolant, and low conductivity fluids. They have no moving parts and are suitable for flow presence detection in compressors and cooling loops. Compact electromagnetic sensors work for conductive fluids such as wastewater, brine, and chemicals. They provide stable speed output even when the fluid is dirty.

Because clean water is conductive enough for an electromagnetic sensor but oil is not, we always ask for fluid type before quoting. This avoids quoting a sensor that cannot physically work. Material selection also matters. A 316L body with PTFE liner and EPDM O-rings handles many industrial fluids. FKM O-rings suit oil and fuel. Pressure ratings up to 40 bar and process temperatures up to 120 °C cover many mid-range plant applications. ATEX Zone 1 versions are available for hazardous areas in oil and gas or chemical storage.

Do not assume one sensor fits every fluid. A paint manufacturer in Southeast Asia asked for a DN15 inline flow sensor for solvent dosing. The solvent had low conductivity. A paddle wheel sensor was not suitable. We supplied a thermal dispersion version with 316L body and FKM O-rings. The output was a 4-20 mA signal tied to a pump interlock. That solved the issue without a full flow meter.

Installation Rules That Prevent Field Problems

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