An in-line flow monitor can be permanently installed in a hydraulic circuit to give an immediate indication of flow without connecting temporary test equipment each time a check is required.

Webtec® offers several approaches. The FI750/1500 and WPB ranges provide direct mechanical indication, while WPM adds an adjustable flow alarm and WPR provides an electrical output for external monitoring. FlowHUB® combines digital flow and temperature measurement with switching and/or analogue transmission, depending on the version selected.

The main considerations are the fluid, flow range, pressure, operating temperature and what you need to do with the measurement.

A mechanical FI or WP flow monitor is suitable where a local visual indication is sufficient. A WPM adds one or two flow alarm switches. A WPR transmits the measured flow to external equipment. FlowHUB® provides digital flow and temperature display together with programmable flow switching, analogue transmission, or both.

Specialised models are also available for water, air and gas, phosphate ester fluids and high-temperature liquid systems. 

Yes. The FI750/1500 and WPB direct-reading flow monitors operate mechanically and do not require an electrical supply.

The FI range uses a metering piston magnetically coupled to a pointer. The WP range uses a sharp-edged floating orifice disc, transfer magnet and return spring, with movement displayed on a calibrated scale. These designs are useful for commissioning, maintenance and continuous local monitoring where electrical power is unavailable or unnecessary. 

All three provide in-line flow measurement, but the level of functionality differs.

The FI750/1500 is a direct-reading mechanical indicator with a large 63 mm / 2½ in dial and optional temperature indication on selected versions. The WP family also provides direct mechanical indication but offers a wider range of specialised versions, including alarm, transmitter, pneumatic, high-temperature and phosphate ester models. FlowHUB® is electronic and combines a digital display, built-in temperature measurement and configurable electrical outputs. 
 

Yes, on selected products.

FlowHUB® measures and digitally displays both flow and temperature as standard. Standard FI750 and brass FI750/1500 models can also be specified with a built-in thermometer.

The WPH is a high-temperature flow monitor rather than a temperature measuring instrument. It is designed to measure flow in higher-temperature liquid systems. 
 

Yes. The Webtec® FlowHUB has two programmable switched outputs which can be used to trigger an alarm or shut down equipment if the flow moves out of a set range. The WPM Series uses one or two adjustable Form C dry-contact switches that can signal when flow passes a defined level. The contacts can be used to operate a warning, alarm or process shutdown and can be configured for increasing or decreasing flow.

Yes. FlowHUB® Ultimate combines two programmable switched outputs with either a 0–5 V or 4–20 mA transmitter output.

This allows one component to display the measured condition, operate an alarm or control function and send the flow value to a PLC or other monitoring system. WPM and WPR instead provide dedicated alarm and transmitter functions respectively. 

The WPR Series converts measured flow into an electrical output suitable for external instrumentation and control equipment. Available outputs include 4–20 mA, 0–5 VDC, 1–5 VDC and 20–2,000 Hz square-wave pulse, depending on configuration. Response time is specified at less than 100 ms.

FlowHUB® Transmitter and Ultimate versions provide either a 0–5 V or 4–20 mA output.

Several models are available, but fluid compatibility and calibration need to be selected correctly.

The brass FI750/1500 Series contains no carbon-steel parts and is specifically intended for water, water-oil emulsions and hydraulic oil. WPB is available in brass or stainless-steel construction calibrated for either oil or water,. WPM and WPR can also be configured for water monitoring.

The seal and material combination should always be checked for the actual fluid being used. 

Webtec® offers both FI and WP products specifically for phosphate ester service.

The FI Phosphate Ester Series is a direct-reading FI750/1500 design using EPDM seals and is intended for applications including aviation ground support equipment. It covers calibrated flow ranges up to 250 L/min / 66 US gpm depending on model.

The WPP Series is calibrated for phosphate ester at 1.145 specific gravity and offers ranges up to 500 L/min / 130 US gpm, with aluminium, brass or stainless-steel construction. 

Yes. The WPG Series is specifically designed for pneumatic applications such as checking compressor output, pneumatic-tool air consumption and industrial gas flow.

Its available ranges extend up to 1,300 SCFM / 600 SLPS, with pressure capability dependent on material. Stainless-steel versions are listed up to 69 bar / 1,000 psi.

Pneumatic configurations are also available within the WPM alarm and WPR transmitter families.

The WPH Series is designed specifically for continuous or intermittent flow monitoring in high-temperature liquid systems. It is not suitable for steam.

The current datasheet specifies a maximum operating temperature of 204 °C / 400 °F. Aluminium, brass and stainless-steel constructions are available, and the exact pressure and flow capability should be checked against the selected configuration.

The available range depends on the product family.

Standard aluminium FI750 indicators cover ranges up to 180 L/min / 48 US gpm, while brass FI750/1500 versions extend to 400 L/min / 100 US gpm. WPB hydraulic monitors have selectable ranges up to 550 L/min / 150 US gpm. FlowHUB® metric models extend to 360 L/min, while separate US-unit models are also available.

Selecting a range appropriately matched to the normal operating flow is important because product accuracy is generally specified as a percentage of full scale. 
 

For the current WP liquid-monitor configurations, maximum pressure depends on construction.

Aluminium and brass versions are listed at 240 bar / 3,500 psi, while stainless-steel versions are listed at 420 bar / 6,000 psi. This applies to WPB and is also reflected in the liquid configurations of WPH, WPM, WPP and WPR ordering tables.

Air and gas models use lower pressure ratings. 

Accuracy depends on the product and fluid.

The FI flow indicators are specified at ±4% of full scale. FlowHUB® standard flow accuracy is ±3% of full scale at 21 cSt. WPB, WPH and WPP standard unidirectional liquid versions are specified at ±2% of full scale.

For WPG air and gas monitoring, the detailed specification gives ±2.5% of full scale in the centre third of the measuring range and ±4% in the upper and lower thirds. WPM and WPR use the same air/gas accuracy figures, while their oil and water versions are ±2% of full scale.

Yes. Fluid viscosity can affect flow measurement, although the different product designs address this in different ways.

The FI and WP mechanical ranges use sharp-edged orifice designs intended to minimise the effect of viscosity changes. FlowHUB® is calibrated at a mean viscosity of 21 cSt using ISO32 hydraulic mineral oil, and its datasheet provides specific guidance on the effect of viscosity.

For WPM and WPR, standard viscosities up to 110 cSt are specified, with Webtec consultation recommended between 110 and 430 cSt.

Not with the WP or FlowHUB® ranges.

The current WP datasheets state that straight lengths of pipe are not required at either the inlet or outlet, which can simplify installation where space is limited. WP monitors can also be mounted without restriction to orientation.

FlowHUB® incorporates built-in flow conditioning, so the normal requirement for approximately ten pipe diameters of straight inlet pipe is also unnecessary.

Yes. The FI, WP and FlowHUB® families can all be installed in different orientations, although their installation requirements differ.

The FI750/1500 can be installed horizontally, vertically or between the two, but its magnetic measuring mechanism should be kept clear of nearby ferrous material when panel mounted. WP products have unrestricted mounting orientation. Most sizes of FlowHUB® can be installed in any orientation, although special calibration may be required for some installations. 

The capability varies by product, so reverse flow should not be assumed.
Standard FI750/1500 and FI Phosphate Ester indicators should not be operated with reversed flow because the datasheets state that they may be damaged and act as a non-return valve.

FlowHUB® permits reverse flow but does not measure the reverse flow rate.

WPB and WPH can be specified as unidirectional, reverse-flow or, on selected flow ranges, bi-directional versions. WPG, WPM, WPP and WPR offer unidirectional or reverse-flow configurations rather than a bi-directional option in their current ordering tables. 

Requirements depend on the product family.

WPB, WPG, WPH, WPM, WPP and WPR specify a minimum filtration requirement of 74 micron filtration or a 200 mesh screen.

FlowHUB® requires a maximum 40 micron filter, with oil cleanliness better than NAS 8 or ISO 19/17/14.

The FI datasheets supplied do not state an equivalent filtration figure, so the WP or FlowHUB® requirements should not be applied to the FI range by assumption.

Yes, but the ordering requirements vary.

FlowHUB® and the FI ranges state that calibration certificates are available on request as a chargeable option.

For the WPB, WPG, WPH, WPM, WPP and WPR ranges, calibration certificates are also available at extra cost, but the current datasheets specifically state that they must be requested at the time of order and cannot be requested retrospectively. 

A flow alarm is useful when the main requirement is to take action when flow crosses a defined limit. The WPM provides dry-contact switching which can be used for warnings, alarms or process shutdowns.

A transmitter is more suitable when the actual flow value needs to be sent continuously to a PLC, data acquisition system, display or controller. The FlowHUB® and the WPR provides proportional analogue or pulse outputs for this purpose.

Where both alarm switching and an analogue flow signal are required in one device, FlowHUB® Ultimate provides both functions. 

For a straightforward local check of pump delivery, a direct-reading mechanical flow indicator is often suitable because no power supply or external display is required.

The FI750 is specifically described for quick checks of pump performance and setting flow-control valves. WPB is likewise designed for monitoring pump performance and media flow through hydraulic circuits and cooling systems.

If you need to test the pump performance, Webtec offers dedicated hydraulic testers that measure flow, pressure and temperature and include a built in load-valve, like the RFIK series.