Mass Flow Controllers & Meters


Whisper™ MCDW–Series: Low Pressure Drop Bidirectional Gas Mass Flow Controllers

Alicat Whisper™ MCDW–Series low pressure drop bidirectional mass flow controllers are ideal for controlling mass and volumetric flow rates when there is little available system pressure. Low pressure drop minimizes system impact, enabling flow control at near-atmospheric pressures and shortening system response times. Alicat’s MCDW brings the benefits of low pressure drop to our incredibly versatile MCD bidirectional flow controller.

Control flows into your flowing or closed process in one direction, and then reverse flow with multivariate measurement of flow, pressure and temperature in each direction. Or control flow into a closed process using pressure control while monitoring flow rates, and then vent the volume with no need for additional bleed valves. We’ll use your application parameters to customize your valve and PID tuning to ensure that it delivers fast and stable control, in both directions.

  • Versatile. Control flow with positive pressure or vacuum in one or both directions. Or control pressure into flowing or dead-ended processes. (Download our infographic on the right for flow diagrams.) In all cases, flow measurement is multivariate (mass flow, volumetric flow, pressure and temperature), and you can select another gas calibration on the fly or define your own gas composition with COMPOSER™.
  • Connected. Easy integration into your digital industrial network with EtherNet/IP, EtherCAT, DeviceNet, Profibus, Modbus (RTU and TCP/IP) or serial communications options.
  • Durable. Backed by annual recalibrations and our limited lifetime warranty, an Alicat instrument will keep your process running smoothly, even in challenging environments, for years to come.

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  • Available ranges: max –5000 to +5000 SLPM; min –0.5 to +0.5 SCCM
  • Steady state control range: 0.05% – 100% of full scale
  • Standard accuracy calibration, NIST–traceable: ±0.75% of reading or ±0.1% of full scale (most products)
  • Optional high-accuracy calibration, NIST–traceable: ±0.6% of reading or ±0.1% of full scale (most products)
  • Repeatability: ±(0.2% of reading + 0.02% of full scale) (most products)
  • Typical control response time: as low as 30 ms
  • Warm-up time: <1 s
Operating conditions
  • Compatible gases: 98 pre-loaded selectable gas calibrations; additional mixtures definable with COMPOSER™
  • Operating temperature: –10°C to +60°C
  • Full scale operating pressure: 60 PSIA
  • Proof pressure: 80 PSIA
  • STP/NTP: user-selectable (defaults: 25°C & 1 ATM (STP); 0°C & 1 ATM (NTP))
Model variations
Valve options 

Your mass flow controller may be customized with one of the following valving options to ensure optimal performance under your expected process conditions.

  • MCDW: small proportional control valve for flow ranges of 20 SLPM and below
  • MCRDW: nearly frictionless large Rolamite proportional valve for flow rates of 50 SLPM and above
Build options
  • Communications protocols: analog, RS–232, RS–485, DeviceNet, EtherCAT, EtherNet/IP, Modbus RTU or TCP/IP, PROFIBUS
  • Displays: monochrome or color; integrated or panel-mount
  • Process connections: NPT, SAE, AN, BSPP/G, welded compression, or VCR/VCO fittings
  • Elastomers: Viton, FFKM, EPDM, Silicone
Performance options

Alicat’s MCDW–Series uses small proportional valves for control at lower flow rates and is suitable for use with non–corrosive gases.


Alicat’s MCRDW–Series uses nearly frictionless Rolamite valves and a variety of orifice patterns for control at high flow rates and is suitable for use with non-corrosive gases.


Bidirectional flow vs pressure characterization for respiratory devices

Mimic human respiration with bidirectional flow control into and out of a respiratory device at flow rates consistent with the range of breathing. A low pressure drop Whisper™ configuration (MCRDW) also allows the flow controller to “breathe” slowly with minimal pressure applied.

Bidirectional flow control for remote air sampling and calibration

Sample ambient air with a vacuum pump in one direction, and then periodically calibrate your gas analyzer with positive pressure in the other direction, all without disconnecting any part of the system. A low pressure drop Whisper™ configuration permits volumetric flow sampling at the 16.7 SLPM flow rate. This makes possible the operation and calibration of remote air monitoring stations without human intervention.

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