PD-Series Gas Sample Dryers

Powered by Nafion™ tubing, Perma Pure gas dryers selectively remove water vapor from a gas sample. This selectivity for water vapor allows our dryers to remove more moisture than other gas drying solutions, while keeping analytes in the gas sample.

Unlike our other single-tube gas dryers, Polytube Dryer Series (PD-Series) gas dryers contain multiple Nafion™ tubes bundled together allowing for a higher volume of gas movement in a shorter sample path. This makes the PD-Series the ideal choice for high flow rate gas drying applications (up to 40 lpm). Because of this greater surface area of Nafion™ tubing, the PD-Series offers our highest drying capacity.

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How it Works

Flow your sample gas through the Nafion™ tubing and flow a dry purge gas outside the Nafion™ tubing, countercurrent to the sample gas flow.

While the partial pressure of water in the purge gas is less than in the sample gas, Nafion™ polymer will selectively transfer water and water vapor from the sample gas across its membrane and into the purge gas flow, yielding a drier sample gas at the sample gas output.


Number of Nafion™ Tubes Inside 50 (PD-50T), 100 (PD-100T), or 200 (PD-200T)
Max Flow Rate 10 lpm (PD-50T), 20 lpm (PD-100T), 40 lpm (PD-200T)
Housing Materials Available Polypropylene, Fluorocarbon, or Stainless Steel
Max Operating Temperatures 80 °C for polypropylene housing, 100 °C for fluorocarbon or stainless steel housing
Sample Gas Port – End Fittings Port 1/4” NPT
Purge Gas Port – End Fittings Port 1/8” NPT
Purge Gas Recommendations
  • Purge gas must be drier than sample gas
  • Purge gas can be instrument quality air (max -40 °C dew point) or nitrogen
  • Purge gas should flow at 2 or 3 times the sample rate

Alternate methods to using a purge gas are possible, such as recycling the dry sample gas, or pulling vacuum through the purge gas flow path.

Performance by Model

PD-50T Model: Flow rates up to 10 lpm


PD-100T Model: Flow rates up to 20 lpm


PD-200T Model: Flow rates up to 40 lpm


The performance curves above are based upon a sample inlet dew point of 20°C and purge flow rate of 2x the sample flow rate. Consult our team for operation with sample gases condensing above ambient temperature. 

psid (psi-differential) = [sample gas pressure at inlet (psig)] – [sample gas pressure at outlet (psig)], based on atmospheric pressure at outlet. 

Materials Options

MPP Molded polypropylene fittings, polypropylene shell
MPS Molded polypropylene fittings, stainless steel shell
MPR Molded polypropylene fittings, rubber shell
MKA Molded fluorocarbon fittings, anodized aluminum shell
MKS Molded fluorocarbon fittings, stainless steel shell
MKR Molded fluorocarbon fittings, rubber shell
MKC Molded fluorocarbon fittings, corrugated stainless steel shell
MSA Machined stainless steel fittings, anodized aluminum shell
MSS Machined stainless steel fittings and shell
MSR Machined stainless steel fittings, rubber shell
MSC Machined stainless steel fittings, corrugated stainless steel shell

Part Number: Model – Material Code

Example: PD-50T-12-MPP

Physical Dimensions by Model​

Material Codes: MPP*, MPS, MKA, MKS, MSA, MSS
Material Codes: MKC, MSC
Material Codes: MPR, MKR, MSR
PD-50T-12 15.3″ 11.8″ 9.7″ 0.75″ 1.04″ 1.13″
PD-50T-24 23.3″ 19.8″ 17.7″ 0.75″ 1.04″ 1.13″
PD-50T-48 47.3″ 43.8″ 41.7″ 0.75″ 1.04″ 1.13″
PD-50T-72 71.3″ 67.8″ 65.7″ 0.75″ 1.04″ 1.13″
PD-100T-12 15.3″ 11.8″ 9.7″ 1.00″ 1.24″ 1.38″
PD-100T-24 23.3″ 19.8″ 17.7″ 1.00″ 1.24″ 1.38″
PD-100T-48 47.3″ 43.8″ 41.7″ 1.00″ 1.24″ 1.38″
PD-100T-72 71.3″ 67.8″ 65.7″ 1.00″ 1.24″ 1.38″
PD-200T-12 15.3″ 11.8″ 9.7″ 1.00″ 1.24″ 1.38″
PD-200T-24 23.3″ 19.8″ 17.7″ 1.00″ 1.24″ 1.38″
PD-200T-48 47.3″ 43.8″ 41.7″ 1.00″ 1.24″ 1.38″
PD-200T-72 71.3″ 67.8″ 65.7″ 1.00″ 1.24″ 1.38″

*MPP material only available in PD-50T model

Part Number: Model – Material Code

Example: PD-50T-12-MPP



Nafion™ Polymer Selectivity

Nafion™ tubing is highly resistant to chemical attack and exhibits highly selective absorption and transfer of compounds. Most substances completely retained in the sample. Although they do not attack or damage the Nafion™ tubing, some polar organic substances are absorbed and consequently lost from the sample flow path. Ammonia and amines are also absorbed and lost to some degree, for which our scrubbers may be able to help. For additional retention information on specific chemicals, use the following calculator.