Mass Flow Controllers & Meters


MCDW–Low Pressure Drop Bidirectional Gas Mass Flow Controllers

The most versatile gas flow controller, with minimal system impact


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“Whisper” series bidirectional mass flow controllers with low pressure drop 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.


  • Available ranges: max -5000 to +5000 slpm, min -0.5 to +0.5 sccm/-500 sμlm to +500 sμlm  (see Part Numbers for stock ranges)
  • Standard accuracy calibration: +/- (0.8% of the reading + 0.2% of the full-scale range in both directions)
  • Optional high-accuracy calibration: +/- (0.4% of the reading + 0.2% of the full-scale range in both directions)
  • Repeatability: 0.2% of the full-scale range
  • Typical control response time constant: 50-100 ms (as low as 25 ms with PID tuning)
  • No warm-up time required

Operating Conditions

  • Compatible gases: 98 pre-loaded selectable gas calibrations; additional mixtures definable with COMPOSER
  • Operating temperature: -10°C to +60°C
  • Max internal pressure (static): 45 psig (60 psia)
  • Proof pressure: 175 psig (190 psia)
  • STP/NTP: user-selectable (defaults to 25°C & 1 atm STP/0°C & 1 atm NTP)

Model Variations

  • Standard configuration, max 160 psia (MCD)

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 standard 16.7 lpm flow rate. This makes possible the operation and calibration of remote air monitoring stations without human intervention.


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