Perma Pure’s Multitube Dryer for High Flow and High Capacity Drying Applications

Perma Pure PD-Series™ gas dryers are multi-tube Nafion™ tubing gas sample dryers designed for high flow, high performance gas drying applications where having a larger amount of of membrane surface area could improve your drying performance. Multiple tubes are bundled together in parallel to form a high capacity dryer. These dryers can be used to dry to -45°C without removing other compounds. Applications for PD-Series gas dryers include gas sample conditioning for continuous emissions and process monitoring. In these applications, sample gases flowing through the Nafion™ tubing are dried without removing any of the sample analytes. PD-Series gas driers can also be used in small scale process applications. Process applications take advantage of one or more of the unique properties of Nafion™ polymer: highly efficient and selective moisture exchange, ion exchange capabilities, and extreme corrosion resistance.
Product Features:

  • Flow rates up to 40 l/m
  • Lower pressure drop for comparable flow rates
  • Faster response time due to shorter flow path
  • Operating temperatures to max. 120° C
  • Operating pressures to 45 psi (absolute)
  • Straight or flexible configuration
  • Corrosion resistant
  • Standard dew points to – 25° C, with lower values possible (contact factory)
  • No loss of analytes
  • No moving parts

Principle of Operation
PD-Series dryers consists of a bundle of 0.030″ O.D. Nafion™ tubing housed within a single large tube shell. Feed gas flows within the Nafion™ tubing while water vapor absorbs into the tubular membrane walls and is removed. Moisture permeating the tubing is carried away by a dry purge gas within the shell that flows counter-current to the feed. Purge gas should be instrument quality air (-40°C dew point) or nitrogen flowing at two to three times the sample flow rate.

Intelligent Product Numbering System
Perma Pure offers the PD-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 PD dryer according to the selection guide and the part number table below:

1 – Series
PD (Polytube Dryer) Series PD
2 – Number of Tubes
50 – 0.030″ Nafion™ Tubes in Parallel 50T
100 – 0.030″ Nafion™ Tubes in Parallel 100T
200 – 0.030″ Nafion™ Tubes in Parallel 200T
18 – 0.070″ Nafion™ Tubes in Parallel 07018T
60 – 0.060″ Nafion™ Tubes in Parallel 06060T
3 – Dryer Lengths
12″ (30 cm) 12
24″ (60 cm) 24
48″ (120 cm) 48
72″ (180 cm) 72
4 – Housing Material
molded PP fittings, SS shell MPS
molded PP fittings, rubber shell MPR
molded PVDF fittings, anodized aluminum shell MKA
molded PVDF fittings, stainless steel shell MKS
molded PVDF fittings, rubber shell MKR
molded PVDF fittings, corrugated SS shell MKC
machined stainless steel fittings, anodized aluminum shell MSA
machined stainless steel fittings and shell MSS
machined stainless steel fittings, rubber shell MSR
machined stainless steel fittings, corrugated SS shell MSC
dryer element replacement (for two-part fitting) E
dryer element replacement E-M

Recommended Sample Gas Flow Rates:
2-10 lpm: PD-050T Series
4-20 lpm: PD-100T Series
10-40 lpm: PD-200T Series

PD Gas Sample Dryer Performance Curves


The Performance curves above are based upon an inlet dew point of 20°C. 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; a PD-50T-24 should yield an outlet dew point of -6°C, the performance of the 12″ unit. Visit the Purge Gas Configurations page to learn more about the purge methods Perma Pure customers deploy in their equipment.

Calculating PD Series Pressure Drop

ΔP (psid) = 0.0056 * Flow rate (splm) * Length of dryer (inches)
ΔP (psid) = 0.0028 * Flow rate (splm) * Length of dryer (inches)
ΔP (psid) = 0.0014 * Flow rate (splm) * Length of dryer (inches)

PD Series Dimensions

Model Number Overall Length Active Length Port-to-Port Shell
PD-50T-12MPS, MPP 15.3″ 12.5″ 11.8″ 9.7″
PD-50T-24MPS, MPP 23.3″ 20.5″ 19.8″ 17.7″
PD-50T-48MPS. MPP 47.3″ 44.5″ 43.8″ 41.7″
PD-50T-72MPS, MPP 71.3″ 68.5″ 67.8″ 65.7″

Short Video Presentations

Perma Pure has created a series of short video presentations to describe the basic functionality of Nafion™ Tubing and our Gas Sample Dryers. The videos are posted below. View the Nafion™ Tubing video before moving on to the Dryers.

Perma Pure PD Gas Sample Dryers – Full Presentation

Perma Pure Purge Gas Configurations

Nafion™ Tubing Basic Functionality

Perma Pure MD and PD Gas Sample Dryers Basic Functionality