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HMD Series Membrane Air Dryers
| PRODUCT | TYPE | FLOW | RATING |
|---|---|---|---|
| Membrane Air Dryer | Membrane | 0.55 to 29.1 SCFM | 175 psig / 150°F |
Specifications
Configuration & Size
Sizes:
HMD20-1 to HMD20-6, paralleled -7, -8, -9
Flow at -40°F:
0.55 to 29.1 SCFM inlet
Connections:
3/8 in to 1 in NPT or BSP
Housings:
Nylon/CPVC/brass, aluminum or 304 stainless
Features
- No electrics, no moving parts and no liquid condensate: the water leaves as vapor in the sweep
- Mounts in any orientation
- Dew point set by flow, from +50°F down to -40°F on the same module
- Stainless RHD versions for corrosive, hot or cold surroundings
Water vapor out through the fiber wall
A dryer whose dew point depends on how much air you push through it
Inside an HMD module, compressed air flows down the bore of thousands of hollow fibers. Water vapor passes through the fiber wall faster than the air does, and a small stream of the dried air, the sweep, is expanded along the outside of the fibers to carry that vapor away to atmosphere. Nothing moves, nothing needs power, and no liquid is produced, so there is no drain to fail.
Dew point follows flow. At 100 psig and 100°F inlet, the HMD20-5 takes 36.3 SCFM in and delivers 32.1 SCFM at a +50°F dew point, or takes 15.0 SCFM in and delivers 10.8 SCFM at -40°F. The difference between inlet and outlet is the sweep, and it is a larger share of the air at the lower dew point. Size from the outlet flow the tool needs, at the dew point it needs.
The six base modules run from the HMD20-1 at 0.55 SCFM inlet to the HMD20-6 at 29.1 SCFM inlet, both at -40°F. Larger flows come from modules in parallel: the HMD20-7 is three HMD20-5s, the HMD20-8 two HMD20-6s and the HMD20-9 three HMD20-6s. The stainless RHD016SS, RHD026SS and RHD052SS suit corrosive, hot or cold surroundings and are rated at +50°F and +40°F dew points.
HMD Series Applications
Slim modules from 15 to 52 in long
The modules are tubes: the HMD20-3 is 15.3 in long and 4.2 in in diameter at 4.9 lb, and the HMD20-6 is 41.1 in long and 5.3 in across at 14.6 lb on 3/4 in ports. The paralleled HMD20-7, -8 and -9 are 52 in long on 1 in ports and weigh 30 to 45 lb. Ports are NPT or BSP, and a module can hang vertically, lie horizontally or run along a machine frame.
Oil and liquid water foul a membrane for good, so the grade 5 coalescing prefilter is standard and the warranty extends from one year to three with the prefilter package. On a system with heavy contamination, add the grade 7 and grade 3 stages listed for that duty. Leave the sweep port open to atmosphere and never cap or pipe it into a back-pressured line.
Common FAQs
The HMD20-4, which delivers 6.8 SCFM at minus 40°F from 9.3 SCFM in, at 100 psig and 100°F inlet. The next size down, the HMD20-3, gives only 2.72 SCFM at that dew point. Size the compressor and the prefilter for the 9.3 SCFM inlet, not the 5 SCFM the instruments use. If the inlet runs warmer than 100°F, read the flow table at the real temperature before ordering, since 6.8 SCFM leaves little margin on a hot afternoon. The HMD20-4 is a tube 26.9 in long and 4.2 in across, on 1/2 in ports.
Where the housing itself has to survive its surroundings, as in a washdown area, a chemical plant or a coastal cabinet, and a plus 40°F dew point is dry enough. The 304 stainless RHD052SS takes in 45.0 SCFM and delivers 33.6 SCFM at plus 40°F, at 100 psig and 100°F inlet. Each RHD module shares its length, diameter and ports with an HMD20 tube, the RHD052SS matching the HMD20-6, so a corroded module can be changed for stainless without repiping, at lower flow: at plus 40°F the HMD20-6 delivers 55.1 SCFM against 33.6 on the RHD052SS.
Tiny, continuous flows where dry air matters more than volume: an analyzer cell, an instrument enclosure purge, a bubbler level tube or a single valve positioner. At 100 psig and 100°F inlet it delivers 0.34 SCFM at minus 40°F from 0.55 SCFM in, or 1.49 SCFM at plus 50°F from 1.7 in. Flows that small are hard to dry any other way without power. Because the dew point loosens as flow climbs, put a small orifice or flow limiter after the module so a leak downstream cannot pull more air than it can dry.
| Part Number | SCFM in at -40°F | Connection | H x W x D (in) | Weight (lb) |
|---|---|---|---|---|
| HMD20-1 | 0.55 | |||
| HMD20-2 | 2.08 | 3/8 in NPT/BSP | 26.4 x 2.5 | 1.8 |
| HMD20-3 | 3.92 | 3/8 in NPT/BSP | 15.3 x 4.2 | 4.9 |
| HMD20-4 | 9.3 | 1/2 in NPT/BSP | 26.9 x 4.2 | 6.9 |
| HMD20-5 | 15 | 1/2 in NPT/BSP | 41 x 4.2 | 9.5 |
| HMD20-6 | 29.1 | 3/4 in NPT/BSP | 41.1 x 5.3 | 14.6 |
| HMD20-7 | 3 x HMD20-5 | 1 in NPT/BSP | 52 x 19.3 | 30 |
| HMD20-8 | 2 x HMD20-6 | 1 in NPT/BSP | 52 x 12 | 30.7 |
| HMD20-9 | 3 x HMD20-6 | 1 in NPT/BSP | 52 x 21.5 | 45 |
| RHD016SS | 16.3 at +50°F | 1/2 in NPT/BSP | 26.9 x 4.2 | 6.9 |
| RHD026SS | 27.6 at +50°F | 1/2 in NPT/BSP | 41 x 4.2 | 9.5 |
| RHD052SS | 55.2 at +50°F | 3/4 in NPT/BSP | 41.1 x 5.3 | 14.6 |
