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Quotes - Engineering - SalesThe HDF Series
Four sizes, each with an optional prefilter
The HDF Series has four sizes. HDF1 carries 1 lb of gel for 5 SCFM at 100 psig, HDF2 has 2 lb for 10 SCFM, HDF3 holds 4 lb for 20 SCFM and HDF4 holds 6 lb for 30 SCFM. The two smaller sizes have 1/4 in ports and the two larger have 1/2 in. All four are 4 in wide, with heights from 12 to 28 in and weights from 13 to 23 lb.
Each size can be ordered with a coalescing prefilter fitted, marked by a -F suffix on the model, so oil from the compressor does not reach the gel. Replacement gel comes as a kit matched to the size, so the right charge can sit on the shelf beside the booth.
Pressure changes capacity. HDF4 handles 25 SCFM at 80 psig, 30 at 100 and 43 at 150, and the smaller sizes follow the same pattern. Size at the pressure the gun or tool is actually fed.
A charge of silica gel in the air line
Nothing regenerates, so the desiccant is a consumable
A single tower dryer is the simplest desiccant dryer there is: one aluminum housing filled with silica gel, mounted inline close to the tool. Air passes through the gel, water vapor is adsorbed, and dry air leaves through a built-in dust filter. When the gel is loaded its indicator turns from blue to white and the charge is replaced. No purge, no valves, no power.
Ratings
- 200 psig maximum
- 125°F maximum
- Dew points as low as -40°F
Flow at 100 psig
- 5, 10, 20 and 30 SCFM
- Higher at 150 psig
- Lower at 80 psig
Desiccant
- 1, 2, 4 or 6 lb of silica gel
- Blue-to-white color indicator
- Replacement kits by size
Hardware
- Powder-coated aluminum, 4 in wide
- 15 micron cleanable dust filter
- 1/4 in or 1/2 in ports
Single tower sizes
The table lists every size at 100 psig. On a line held at 80 psig expect about four-fifths of the listed flow; at 150 psig the same housing carries close to half as much again.
| MODEL | SERIES | SCFM | CONNECTION | H X W X D (IN) | WEIGHT (LB) |
| HDF1 | HDF Series | 5 | 1/4 in | 13 x 4 | 13 |
| HDF2 | HDF Series | 10 | 1/4 in | 12 x 4 | 15 |
| HDF3 | HDF Series | 20 | 1/2 in | 20 x 4 | 20 |
| HDF4 | HDF Series | 30 | 1/2 in | 28 x 4 | 23 |
Put it behind a refrigerated dryer
Silica gel has a fixed capacity, and saturated air straight from a compressor fills it fast. Behind a refrigerated dryer the air reaching the gel already sits at a 38°F dew point, so the gel only has to take it the rest of the way and lasts many times longer. In most body shops that pairing is the right answer: the refrigerated dryer does the heavy lifting and the single tower polishes the air at the booth.
Reading the indicator
The indicator turns from blue to white as the gel loads. Change the charge when it turns, not weeks later, because by then the dew point at the gun has already risen. The figure of as low as minus 40°F belongs to fresh gel and climbs as the charge takes up water, so the color, not the calendar, is the real service schedule.
Where single tower fits
HVLP paint guns, body shop prep stations, airbrush and detailing lines, and small tools where a few SCFM of very dry air matters and running a purge line or a power cable is out of proportion to the job. Above 30 SCFM, or where air is used all shift, a modular heatless dryer costs less to run.
Mounting and maintenance
Mount it inline close to the point of use and downstream of the shop's main filter and drain, so it sees air that is already free of liquid. The integrated 15 micron dust filter is cleanable; clean it each time the gel is changed. Keep the housing out of direct sun and below its 125°F limit.
Looking after a silica gel charge
Not in a way worth relying on; the dryer is built around fresh charges from the matched replacement kits. Silica gel can be dried in an oven, but any oil it collected stays behind, and indicator gel overheated in an oven loses it's color change. The better saving is upstream: behind a refrigerated dryer and a coalescer the gel loads slowly, and each kit goes much further.
Yellow or brown beads, usually starting at the inlet end, where the gel should be blue or white. Oil coats the surface the water would otherwise reach, so a fouled charge changes color unevenly, stops adsorbing early and lets the dew point at the gun rise while part of the column still looks fresh. Change the gel and the shop coalescer element, and if the staining returns, order the -F version so a coalescer sits directly ahead of the gel.
Silica gel holds less water as it warms, and warm air brings more water to it, so a summer afternoon shortens a charge from both ends. Saturated air at 100°F carries nearly twice the water vapor it carries at 80°F and the same pressure. Behind a refrigerated dryer the effect shrinks, because the air arrives already dried to about a 38°F dew point.
