Adjustable or non-adjustable flow monitor? Selection guide for the ChemTec FAV, LCA, CCM and LPH series

ChemTec offers two fundamentally different types of flow monitors: adjustable models on which you set the switching setpoint yourself to match your process flow, and non-adjustable models with a fixed, factory-set setpoint. Both are switching flow monitors with a digital output, but they are intended for different situations. This article helps you make the right choice.

⏱ approx. 5 minutes reading time

The fundamental difference

All ChemTec flow monitors work on the same basic principle: a moving element in the liquid or gas path responds to the flow and activates a reed switch at a certain flow value. The difference lies in who determines that activation value: the manufacturer during production, or the engineer during installation.

Both types provide a switching output

Both adjustable and non-adjustable ChemTec flow monitors provide a digital switching contact as output: on at normal flow, off when deviating from the setpoint (or vice versa, depending on the NC/NO configuration). The difference lies solely in the setpoint setting, not in the type of output or the function. Both are suitable for connection to a digital PLC input.

The 10:1 ratio as a guideline

ChemTec uses a practical rule of thumb for the selection of adjustable flow monitors: the ratio between the normal process flow and the desired setpoint must be at least 10:1. This is the so-called flow/setpoint ratio, and it is the most direct selection parameter for the adjustable series.

The background to this rule of thumb is mechanical: the adjustable monitor works with a float or piston that is held in position by the process flow. The switching setpoint is close to the activation flow of the moving element. If the process flow is only two or three times as high as the setpoint, the margin is too small for stable operation: small fluctuations in the process flow cause unwanted switching actions. At a ratio of 10:1 or more, there is sufficient dynamic range for stable, chatter-free switching.

With a ratio of less than 10:1, consider the 125 Bypass series or the non-adjustable LPH series with a fixed setpoint that exactly matches your process flow.

Adjustable series: FAV, LCA, CCM and 125 series

ChemTec's three adjustable series are each optimised for a specific application profile. Within the adjustable category, the flow range, the material composition and the geometry of the connection differ.

FAV Series

Flow range: Air: 14 to 3,398 SLPM / Water: 0.4 to 75 LPM

Media: Gas and liquid

Material: Brass or 316 stainless steel

Max. pressure: Up to 3,000 PSI (206 bar) for stainless steel

Ratio rule: Normal flow / setpoint ≥ 10:1

Applications: Hydraulics, cooling systems, heat pumps, fire suppression systems, industrial analysers

LCA Series

Positioning: Economical version for loss-of-flow detection

Media: Corrosive and non-corrosive liquids

Ratio rule: Normal flow / setpoint ≥ 10:1

Applications: Machine lubrication, cooling water, water treatment, chemical processes

Advantage: Lower cost than the FAV for simpler applications

CCM Series

Special feature: Monitoring from 10 cc/min air; lowest flow range of the adjustable series

Configuration: Compact inline for integration into analytical instruments

Media: Corrosive and non-corrosive gases and liquids

Applications: Gas chromatography, dosing systems, analytical instruments

125 / 125 Bypass

125 Series: Ratio ≥ 10:1 for gas analysers, welding and soldering installations

125 Bypass: Ratio 3:1 to 10:1 for cooling systems and industrial liquid lines where a small ratio is common

Advantage: Wide adjustable range with minimal pressure drop

Non-adjustable series: FS, LFS, LPH and LPH UHP

ChemTec's non-adjustable series comprises four models, each with a factory-set switching setpoint that is fixed during production and cannot be changed afterwards. The right selection is made at model level: you choose the model number with the setpoint closest to your desired switching value, and the housing and material that suit your medium.

The shared operating principle of the LPH, FS and LFS is simple and robust: as the flow increases, the pressure differential across a moving element builds up until it overcomes the resistance of that element. The element moves fully to its end position and activates the hermetically sealed reed switch. This is a snap action that also occurs in the falling direction. No external seals in the fluid path, minimal moving parts. The difference between the four series lies in the medium, the housing and the specific application profile.

LPH Series

Setpoint: Fixed per model number; choose the right model when ordering

Media: Corrosive and non-corrosive liquids and gases

Material: Acrylic (visual), brass, 316 stainless steel or Teflon®

Seals: No seals in the fluid path

Indication: Visual flow indication with the acrylic version

Applications: Analysers, laser cooling systems, dialysis equipment, medical equipment, bubbler systems

LPH UHP Series

Special feature: Specifically designed for ultra-high purity gas: semiconductor, cleanroom

Material: 316L stainless steel, EP surface finish down to 10Ra

Connection: ½" MVCR or ¼"/⅜" tube OD weld/tube stub

Output: Reed switch contact output

Delivery: Selected configurations available within 24 hours

Applications: Wafer production, semiconductor gas panels, cleanrooms, H2 installations

FS Series

Positioning: Economical monitoring of higher flows of corrosive and non-corrosive liquids

Media: Corrosive and non-corrosive liquids

Material: 316 stainless steel, brass or PVC

Special feature: No seals, one moving part, low maintenance

Mounting: Vertical inline

Applications: Laser cooling systems, heat pumps, cooling systems

LFS Series

Special feature: Polypropylene housing for chemically resistant applications in which a metal housing is undesirable

Media: Corrosive and non-corrosive liquids

Mounting: Vertical inline

Applications: Deionised water, chemical processes, cooling systems, heat pumps, laser cooling

LPH UHP: no seals, no risk of contamination

The LPH UHP series has no elastomer seals in the fluid path. This is a hard requirement in ultra-high purity gas lines: every seal is a potential source of outgassing or contamination. The reed switch is hermetically sealed outside the gas path in the body of the instrument, so that the gas only comes into contact with the 316L stainless steel surface with an EP finish down to 10Ra.

When do you choose which?

Selection in four steps

1. Is the setpoint known exactly and stable?

If the process flow is stable and you know the desired setpoint exactly, the non-adjustable LPH series is a simple, compact choice. Select the model number with the nearest fixed setpoint. If the setpoint is unknown or variable, choose an adjustable series.

2. Does it concern ultra-high purity gas?

For UHP gases in semiconductor, cleanroom or hydrogen installations, the LPH UHP series is the only correct choice. The 316L stainless steel construction with EP finish and no seals in the gas path are hard requirements in these applications. Other series are not suitable.

3. What is the flow/setpoint ratio?

Calculate the ratio: normal process flow divided by the desired setpoint. If the ratio is 10:1 or greater, the FAV, LCA or CCM will work well. If the ratio is less than 10:1, consider the 125 Bypass series or the LPH with a fixed setpoint close to your desired value.

4. Which flow range and which medium?

For higher flows and higher pressures: FAV. For corrosive liquids with economical requirements: LCA. For low-flow gas in analytical instruments: CCM. For liquid or gas with known setpoints and compact installation dimensions: LPH. For higher liquid flows with a fixed setpoint and metal housing: FS. For deionised water or chemical liquids requiring a polypropylene housing: LFS. Not sure which series? Inacom will advise you based on your specifications.

Rule of thumb for OEM applications

In standardised OEM installations in which hundreds or thousands of identical units are built, the non-adjustable LPH series has a clear advantage: every unit leaves the factory with exactly the same setpoint, without manual adjustment on site. This eliminates deviations between units and reduces assembly and qualification time. The adjustable series offers more flexibility for prototypes and small series in which the final process parameters have not yet been determined.

Adjustable flow monitors

Non-adjustable flow monitors