MD Series Gas Sample Dryers

mdhome1 Further Information:

Perma Pure MD™-Series gas sample dryers use exclusive Nafion™ selectively permeable membrane tubing to continuously dry gas streams removing only water vapor. These dryers operate over a wide range of temperatures, pressures and flow rates, and dry to dew points as low as -60°C.

Product Features:

  • Flow rates up to 4 l/m
  • Operating temperatures to max. 120° C
  • Operating pressures to 100 psi (absolute)
  • Straight or coiled configuration
  • Corrosion resistant
  • Standard dew points to – 25° C, with – 60° C possible in special cases (contact factory)
  • No loss of analytes
  • No moving parts

Principle of Operation

MD-Series gas dryers transfer moisture from one gas stream to a counter-flowing purge gas stream, much like a shell-and-tube heat exchanger transfers heat. Water molecules permeate through the Nafion™ tube wall, evaporating into the purge gas stream. The water concentration differential between the two gas streams drives the reaction, quickly drying the air or gas. Purge gas should be dry (-40°C dew point) air or other gas. If no dry gas is available, a portion of the gas dried by the MD-Series dryer can act as the purge gas in a split-stream or reflux method. Visit the Purge Gas Configurations page to learn more about the purge methods Perma Pure customers deploy in their equipment.

Intelligent Product Numbering System

Perma Pure offers the MD-Series dryer with three sizes of Nafion™ tubing and in a variety of lengths and connection types. Choose the size based on your flow rate and dryness requirement and build your MD dryer according to the selection guide and the part number table below:


1 – Series
MD (Monotube Dryer) Series MD
2 – Tubing Size
0.050″ Nafion™ Tubing 050
0.070″ Nafion™ Tubing 070
0.110″ Nafion™ Tubing 110
3 – Dryer Lengths
12″ (30 cm) 12
24″ (60 cm) 24
48″ (120 cm) 48
72″ (180 cm) 72
96″ (240 cm) 96
144″ (360 cm) 144
288″ (720 cm) 288
4 – Shell and Connector Material
Polypropylene (PP) P
Fluorocarbon (FEP / PVDF) F
FEP Shell, PP Connectors FP
Stainless Steel S
FEP Shell, Stainless Connectors FS
Element Only (for spare part) E
5 – Connector  / Spare Part Type
Sample Gas Connector Type
1/16″ Compression (MD-050 only) 1
1/8″ Compression 2
1/4″ Compression 4
Spare Part Type
Element, PTFE Inserts, EP O-Rings P
Element, PTFE Inserts, Viton O-Rings F
Element, SS Inserts, Viton O-Rings S

Recommended Sample Gas Flow Rates:
0-0.2 lpm: MD-050 Series
0.1-2 lpm: MD-070 Series
1-4 lpm: MD-110 Series

Notes: 1MD-050 dryers are not offered in 96 and 144 inch lengths. 2MD-070 and MD-110 offer approximately the same drying performance. Specify MD-110 when pressure drop is a concern, MD-070 to minimize dead volume. For higher flow rates, please see our PD-Series dryers.

Select Your Dryer by Flow and Target Dew Point (Moisture Level)

MD Dryer Series Performance Curves


NOTE: The pressure drop is per inch of dryer. For example, the pressure drop of 100 ml/min through an MD-050-24 is equal to 2.4 inches of water. These performance curves are based upon an inlet sample dew point of 20°C, a purge gas with a dew point of -40°C, and a purge flow rate which is 2-3 times the sample flow rate. For conditions higher than ambient temperature, it is assumed that the first half of the dryer will be used to bring the dew point down to ambient. For this reason, read the value of the next shorter dryer. For example, a stream with an initial dew point of 50°C, flowing at 2 slpm; an MD-070-48 should yield an outlet dew point of 6°C, the performance of the 24″ unit.


Model Number A B C D E A D E
Single Tube of 0.050″ O.D. Nafion

Fluorocarbon or Polypropylene

Stainless Steel

For Engineering drawings, click part number: MD-050-F or P MD-050-S
MD-050-12 1/8″ 1/8″ 1/8″ 14″ 10-5/8″ 1/8″ or 1/16″ 14″ 11-1/2″
MD-050-24 1/8″ 1/8″ 1/8″ 26″ 22-5/8″ 1/8″ or 1/16″ 26″ 23-1/2″
MD-050-48 1/8″ 1/8″ 1/8″ 50″ 46-5/8″ 1/8″ or 1/16″ 50″ 47-1/2″
MD-050-72 1/8″ 1/8″ 1/8″ 74″ 70-5/8″ 1/8″ or 1/16″ 74″ 71-1/2″
Single Tube of 0.070″ O.D. Nafion Fluorocarbon or Polypropylene Stainless Steel
For Engineering drawings, click part number: MD-070/110-F or P MD-070/110-S
MD-(070 or 110)-12 1/4″ or 1/8″ 1/4″ 1/4″ 14-1/4″ 10″ 1/4″ or 1/8″ 13-3/4″ 10-3/4″
MD-(070 or 110)-24 1/4″ or 1/8″ 1/4″ 1/4″ 26-1/4″ 22″ 1/4″ or 1/8″ 25-3/4″ 22-3/4″
MD-(070 or 110)-48 1/4″ or 1/8″ 1/4″ 1/4″ 50-1/4″ 46″ 1/4″ or 1/8″ 49-3/4″ 46-3/4″
MD-(070 or 110)-72 1/4″ or 1/8″ 1/4″ 1/4″ 74-1/4″ 70″ 1/4″ or 1/8″ 73-3/4″ 70-3/4″
MD-(070 or 110)-96 1/4″ or 1/8″ 1/4″ 1/4″ 98-1/4″ 94″ 1/4″ or 1/8″ 97-3/4″ 94-3/4″
MD-(070 or 110)-144 1/4″ or 1/8″ 1/4″ 1/4″ 146-1/4″ 142″ 1/4″ or 1/8″ 145-3/4″ 143-3/4″

Perma Pure has created a series of short video presentations to describe the basic functionality of some of our products. The videos are posted below.

Nafion™ Tubing Basic Functionality

Perma Pure MD and PD Gas Sample Dryers Basic Functionality


Nafion is not only highly resistant to chemical attack, it also exhibits highly selective absorption and transfer of compounds. Most substances are retained quantitatively. Although they do not attack or damage the Nafion tubing, some polar organic substances are absorbed and consequently lost. Ammonia and amines are also absorbed and lost to some degree. For retention information on specific chemicals, use the following pull down menu.

Perma Pure Dryer App

PP-Apple-App PP-Android-App

Guide to Gas Sample Drying


Free White Paper

All About Nafion


Technical Information

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