Choose the drain around the filter's actual pressure cycle and condensate load. Manual draining needs an operator; air-shutoff draining needs depressurization; automatic draining needs its specified operating conditions. A stopped machine can still have a pressurized filter, so stopping production does not necessarily trigger drainage.
Why is the filter not draining after the machine stops?
Imagine a machine finishing its shift while the compressed-air main stays on. The cylinders stop moving, but the filter bowl remains under pressure. An air-shutoff drain may therefore have no reason to open. Before treating retained water as a failed drain, identify the fitted mechanism and check whether pressure was actually released at the filter. Closing an upstream valve can also leave pressure trapped downstream. The machine's approved isolation and depressurization procedure determines how that pressure is safely removed.
Compare the three drain behaviours
Drain names describe different triggers. Manufacturer literature also uses semi-automatic or overnight drain for drainage associated with depressurization. Parker distinguishes this behaviour from other automatic mechanisms. [2] The XMC HDA catalogue uses the term air-shutoff drain. [1] When comparing suppliers, ask when the quoted drain opens instead of relying on the word automatic alone.
| Drain type | What triggers drainage | Where to consider it | What to confirm |
|---|---|---|---|
| Manual | An operator actuates the drain as instructed. | Accessible filters with manageable accumulation and a reliable inspection routine. | Safe operating procedure, access and drainage frequency. |
| Air-shutoff | Depressurization under the drain's required conditions. | Stations regularly isolated and depressurized through an approved procedure. | Pressure actually reaches the required state at the filter; stopping the machine alone is insufficient. |
| Automatic option | The specified automatic mechanism operates within its rated conditions. | Continuous duty or frequent accumulation where manual drainage would be difficult to sustain. | Exact mechanism, operating pressure, discharge capacity and outlet installation. |
What the HDA catalogue specifies
The 21 June 2025 XMC catalogue gives the following drain-function entries for HDAF filters, HDAW filter-regulators and HDAC two-piece and three-piece combinations. [1] These are body-size distinctions, not a promise that every port, gauge, bowl and drain combination is available. Check the complete specification when ordering a single filter or an assembled FRL.
| Body size | Catalogue drain-function entry |
|---|---|
| 20 | Manual drain. |
| 30 and 40 | Air-shutoff drain; automatic drain available as an option. |
Match the drain to the working day
For an accessible machine used intermittently, manual drainage can be a practical choice if someone checks the bowl and empties it as instructed. For a station routinely depressurized after each shift, review air-shutoff drainage against the actual shutdown sequence. For a line that remains pressurized across shifts, discuss an automatic option that can discharge during those conditions. Base the decision on observed condensate accumulation as well as operating hours: a long-running station supplied with well-treated air can behave differently from a lightly used station receiving wetter air.
Check pressure and the discharge route
Printed page 52 lists HDAF working pressure from 0.15 to 1.0 MPa and vertical installation within plus or minus 5 degrees. [1] Those filter specifications do not provide the selected drain's complete opening-and-closing behaviour. Confirm normal and startup pressure at the filter, the required drainage conditions and permitted discharge piping. Other manufacturers distinguish normally open and normally closed automatic drains by their unpressurized state; those labels cannot be assigned to an HDA option without confirmation. [3]
Read the full ordering code
The HDAF ordering diagram identifies D as the automatic-drain option. Its examples show HDAF30-03 as a 3/8-port filter with air-shutoff draining, and HDAF30-03D-1 as a 3/8-port filter with automatic draining plus the A-series bowl and protective-cover option. [1] The latter changes both drain and bowl selection. When replacing a filter, send the complete existing code and a clear label photograph. A shared body size or port size alone does not establish identical configuration.
If water still remains in the bowl
Identify the drain before troubleshooting it. For a manual unit, check whether the instructed drainage routine has been carried out. For an air-shutoff unit, establish whether its required depressurization event occurred. For an automatic option, compare the actual operating conditions with its supplied instructions. Inspect the visible discharge route for kinks or blockage and confirm the installation orientation. Persistent accumulation under suitable conditions needs service review. Follow the approved isolation and depressurization procedure before opening the bowl or dismantling the drain; never loosen a pressurized bowl to empty it.
Keep drainage and air quality separate
An automatic drain removes collected liquid under its operating conditions; it does not establish an air-drying specification. The HDAF and HDAW tables list 25 micrometres as the standard filter rating, with 5 and 50 micrometre options. [1] Those particle ratings are not pressure-dew-point ratings. State the downstream equipment's required air quality when reviewing the whole treatment arrangement. Keep inspecting the bowl and discharge function after fitting an automatic drain; it still requires maintenance.
Send XMC the details that decide the drain
Include the HDAF, HDAW or HDAC model and full option code, port and thread requirement, normal and startup pressure, daily operating hours, and whether the filter remains pressurized at shutdown. Describe observed condensate accumulation, access to the bowl and the proposed discharge route. A photograph of the label and surrounding installation helps us review the application. Ask for confirmation of the available drain and bowl combination, its operating requirements and maintenance instructions before ordering.
Continue planning your HDA station
Drain selection is one part of specifying an air-preparation station. Use the combination guide to compare the two-piece FR+L and three-piece F+R+L layouts. If the downstream equipment requires lubrication, the HDAL guide explains minimum misting flow and what to check when oil is not dripping.
Catalogue and terminology references
XMC model details in this guide come from the dated HDA catalogue. Parker and CKD are cited only to explain general drain terminology; their product ratings and operating instructions do not define the performance of an XMC drain.
Questions buyers ask.
Is an air-shutoff drain the same as an automatic drain?
In the HDA catalogue they are distinct selections. Air-shutoff draining depends on depressurization; the automatic option has its own operating requirements. Confirm the mechanism on the quoted model.
Why does my filter not drain when I switch the machine off?
The filter may still be pressurized. Electrical shutdown or stopping a machine cycle does not necessarily release compressed air. Verify the fitted drain and actual pressure state before diagnosing a fault.
Can I specify an automatic drain on every HDAF20?
The cited table lists manual draining for body size 20. Ask XMC to confirm the exact requested configuration; do not infer availability from the general ordering diagram.
How often should I drain a manual air filter?
Follow the supplied instructions and establish the inspection routine from actual condensate accumulation. A universal once-a-day interval may be unsuitable when moisture load or operating hours change.
Technical references
- [1] XMC product catalogue, edition 21 June 2025: printed pages 48 and 50, HDAC combinations; page 52, HDAF specifications and ordering examples; page 58, HDAW filter-regulators.
- [2] Parker Hannifin, catalogue 0700P-E, page C12: semi-automatic, automatic pulse and float drain terminology. General mechanism reference only.
- [3] CKD Technopedia, Pneumatic Systems Control Components, Air Filter Drain Discharge: normally open and normally closed terminology. No CKD ratings are assigned to HDA products.
Put the guide to work.
Choose the relevant XMC series, download its product PDF and include the application details with your inquiry.