Compressed Air & Gas Dryers

Membrane Dryer

Dry air right where your machine needs it, running silently on compressed air alone.

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A membrane dryer module mounted beside its coalescing filter with a digital indicator on the filter head

Product overview

Dry air at the point of use, with nothing to plug in

Our membrane dryer dries your compressed air as it flows along a bundle of polymer hollow fibres. Water vapour passes through the fibre walls many times faster than oxygen and nitrogen, so the moisture leaves while your air carries on to the outlet.

There is no electrical supply, no motor, no cycling valve and no desiccant to regenerate. Drying runs continuously and silently for as long as air flows, and the water leaves as vapour in a small, steady exhaust stream, so there is no condensate at the dryer and no drain to fit.

It is commonly selected for ISO 8573-1:2010 water Class 4, 3 or 2: a pressure dew point (PDP) of +3 °C, −20 °C or −40 °C, or lower. Light and compact, it mounts at the machine, instrument or enclosure that needs drier air than your network supplies.

A membrane dryer module mounted beside its coalescing filter with a digital indicator on the filter head
  • −40 °CPressure dew point, ISO 8573-1 Class 2
  • 99.8 %Of the water vapour removed at −40 °C PDP
  • ZeroElectrical supply at the dryer
  • NoneMoving parts to wear

Benefits

The problems it solves

Air leaves your aftercooler saturated, and every pipe, fitting or instrument cooler than the air condenses more water. Here is what that does, and how the dryer stops it.

  • Sticking and frozen instruments

    The problem

    Water in pneumatic positioners, transmitters and relays causes drift and sticking, and ice stops them working entirely.

    How it solves it

    Dried at the instrument to a dew point below the coldest point on its line, your air carries no liquid and no ice. ISA-7.0.01 asks for at least 10 °C below the lowest ambient, and never above +4 °C.

  • No power where you need dry air

    The problem

    Hazardous zones restrict electrical equipment and hot surfaces, and remote sites and vehicles often have no mains supply.

    How it solves it

    The dryer works on compressed air alone, with no electrical parts and no hot surfaces, so it can go into ATEX and IECEx zones, onto vehicles and out to remote sites.

  • One machine needs drier air

    The problem

    A central dryer serves the whole plant at one dew point, but some consumers need drier air, sit at the end of long outdoor branches or were added later.

    How it solves it

    Mounted at the branch or the machine, it raises the water class for that one consumer without re-treating every cubic metre your plant uses.

  • Rust inside pipes and valves

    The problem

    Rust particles block small orifices and nozzles and score valve seats.

    How it solves it

    In a pipe at 20 °C, air at −20 °C PDP has a relative humidity of about 4.4 %, well below the roughly 60 % at which steel starts to corrode rapidly.

  • Dips at sensitive equipment

    The problem

    Analysers and air bearings are disturbed by pressure dips and dew point steps in their supply.

    How it solves it

    Water permeates steadily along the fibres, so your outlet pressure and dew point hold steady, with no blowdown noise.

  • Spoiled finishes

    The problem

    Water in spray air causes blistering, fisheyes and poor adhesion.

    How it solves it

    Drying at the booth keeps water out of your spray guns, even where the plant network only supplies filtered air.

Where it’s used

Wherever one consumer needs drier air

Your plant network sets one dew point for everything. A membrane dryer gives the instrument, booth or machine that needs more its own dry supply.

  • Test tubes of coloured chemicals in a laboratory rack

    Process instrumentation

    Control valves, positioners and transmitters in oil and gas, refining, chemical and power plants, and purge air in hazardous areas.

  • A hand mixing paint in open tins of colour

    Paint and coating booths

    Point-of-use drying that stops spray guns spitting water, which causes blistering and fisheyes.

  • Wine bottles moving along a bottling line

    Food and beverage

    Individual packaging and filling stations fed from general plant air.

Also analysers and FTIR purge, laboratories and dental practices, air bearings in measuring machines, laser optics, telecommunications waveguides and cables, outdoor and cold-store air lines, service vehicles and off-grid sites, and machine builders fitting dryers into their own equipment.

How it works

Filter, permeate, sweep

Your air flows inside a bundle of hollow fibres. Water vapour escapes through the fibre walls, and a small share of the dried air sweeps it away.

How a membrane dryer works: wet compressed air passes through coalescing filters into a bundle of hollow fibres. Water vapour escapes through the fibre walls and dry air leaves for the point of use. A share of the dry air is expanded through a sweep orifice, flows back along the outside of the fibres collecting the water, and vents to atmosphere. Wet air in35 °C · saturated Coalescing filters1 µm0.01 µm Condensate out Hollow fibre membrane module Dry air outPDP down to −40 °CPressure regulator Sweep orificenear atmospheric Humid sweepto atmosphere10 % to 25 % of inlet flow 12345Wet compressed airDry airSweep air, expandedWater vapourLiquid from the filtersYour plant’s equipment

  1. 1. FilterSaturated air passes through a 1 µm coalescing filter and then a 0.01 µm high-efficiency coalescing filter on the dryer inlet, which remove liquid water, oil aerosol and particles. Their automatic drains discharge the liquid.

  2. 2. PermeateThe air divides among the fibre bores. As it travels along them, water vapour dissolves into the fibre wall, diffuses through it and escapes into the shell, while oxygen and nitrogen largely stay inside.

  3. 3. DeliverDried air collects in the outlet end cap and leaves for your point of use, at the dew point the dryer was selected for, down to −40 °C PDP.

  4. 4. SweepA metered share of the dried air passes through the sweep orifice and expands to near atmospheric pressure, which makes it roughly eight times drier, in partial pressure terms, than the air it was taken from.

  5. 5. VentThe sweep air flows back along the outside of the fibres, against the feed, collecting the water, and vents to atmosphere at the feed end. The water leaves as vapour, so there is nothing to drain.

Typical figures at 7 bar g, with saturated inlet air at 35 °C.

Get the full details

Our brochure covers it in detail, and our questionnaire tells us what we need to recommend the right one for your plant.

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