The Caleffi 251003A is a DISCAL solar air separator (deaerator) with a 3/4 in. female threaded connection, for continuous removal of entrained air down to microbubble level from a closed solar thermal circuit. It is the compact version for vertical pipes.
Specifications sourced from Caleffi technical brochure 01134/10 GB and installation instructions 28059.05 NA. Last reviewed August 2026.
Key Features
Removes Air Down to Microbubbles
A stainless steel internal element arranged like spokes creates the swirl needed for dissolved air to come out of solution and adhere as microbubbles, which coalesce and vent automatically.
Continuous Operation, Not Just Fill
Caleffi describes the DISCAL deaerator as discharging air from the circuit continuously and automatically during system operation, keeping the circuit fully deaerated.
Vents at Full System Pressure
Internal geometry is designed to discharge air at pressures up to 150 psi (10 bar), so separation continues at normal solar loop operating pressure.
Compact Vertical-Pipe Version
The 3/4 in. code is the compact version for vertical pipes and is supplied without the 1/2 in. drain port found on the 1 in. and 1-1/4 in. horizontal-pipe versions.
Flow Direction Independent
DISCAL devices work regardless of which way the medium flows through them, simplifying layout. Caleffi recommends installation upstream of the pump on the return, low in the circuit.
Corrosion-Resistant Construction
Chrome-plated brass EN 12165 CW617N body and cover, brass EN 12164 CW614N float guide, dezincification-resistant obturator stem, stainless steel element, lever and spring.
Technical Specifications
| Product Type | Solar Air Separator |
| Application | Closed solar thermal systems |
| Series | DISCAL |
| Connections | 3/4 in. female threaded |
| Connection type | Female Threaded |
| Medium | water, glycol solutions |
| Max. percentage of glycol | 50 % |
| Working temperature range | -30 to 160 deg C (-22 to 320 deg F) |
| Max. working pressure | 150 psi (10 bar) |
| Max. discharge pressure | 150 psi (10 bar) |
| Version | compact, for vertical pipes, without drain |
| Max. recommended medium velocity | 1.2 m/s |
| Dimensions | A 3/4 in.; B 78 mm; C 55 mm; D 143 mm; E 162 mm (letters per dimension drawing in brochure 01134/10 GB) |
| Body and cover | brass EN 12165 CW617N, chrome plated |
| Float | high-resistance polymer |
| Internal element | stainless steel |
| Float guide | brass EN 12164 CW614N |
| Obturator stem | dezincification-resistant alloy EN 12164 CW602N |
| Float lever | stainless steel |
| Spring | stainless steel |
| Hydraulic seals | high-resistance elastomer |
| Manufacturer-listed weight | 0.91 kg (approx. 2.0 lb) |
Documentation
Related Products
- Caleffi 251004A : DISCALAIR Solar Air Vent 3/4" MNPT x 1/2" FNPT
- Caleffi 250041A : Solar Automatic Air Vent 1/2" MNPT
- Caleffi NA29284 : Solar Air Vent Shut-Off Valve 1/2" FNPT x 1/2" MNPT
- Caleffi 253040 : Solar Safety Relief Valve 150 psi
Frequently Asked Questions
What does Caleffi 251003A do?
It continuously separates and discharges entrained air, down to microbubble level, from a closed solar thermal circuit. A stainless steel internal element creates the swirl that lets microbubbles coalesce and rise to a float-operated vent.
How is an air separator different from an air vent?
Caleffi describes the DISCAL deaerator as removing air continuously from the circuit down to microbubble level during normal operation, using a metal screen element that promotes release and adhesion of microbubbles. An automatic air vent discharges air that has already collected at the device.
Is Caleffi 251003A NPT threaded?
Caleffi technical brochure 01134/10 GB and installation instructions 28059.05 NA both specify a 3/4 in. female threaded main connection but do not state the thread standard. Confirm NPT with Caleffi North America before specifying against an existing NPT fitting.
Does Caleffi 251003A have a drain connection?
No. The 3/4 in. code is the compact version for vertical pipes. The 1/2 in. female drain with plug is fitted only to the 1 in. and 1-1/4 in. horizontal-pipe versions.
Where should Caleffi 251003A be installed?
Vertically, upstream of the pump where the pressure drop encourages microbubble formation, and on the return in the lower portion of the solar circuit where no steam forms. Flow direction through a DISCAL device does not matter.
What is the temperature and pressure rating of Caleffi 251003A?
Caleffi publishes a working temperature range of -30 to 160 deg C (-22 to 320 deg F), maximum working pressure 150 psi (10 bar) and maximum discharge pressure 150 psi (10 bar), with water or glycol solutions to 50 %.
What is the warranty on Caleffi 251003A?
Caleffi North America covers this product under its two-year limited warranty against defects in material and workmanship from the date of shipment. ZOT Supply is an authorized Caleffi distributor.
- Product Type:
- Solar Air Separator
- Application:
- Solar Thermal
- Series:
- DISCAL
- Connection Type:
- Female Threaded
- Connection Size:
- 3/4 in.
- Max Operating Pressure:
- 150 psi (10 bar)
- Max Discharge Pressure:
- 150 psi (10 bar)
- Medium Temperature Range:
- -30 to 160 deg C (-22 to 320 deg F)
- Max Glycol Concentration:
- 50 %
- Body Material:
- Brass, chrome plated
