The Caleffi 251004A is a DISCALAIR high-performance solar automatic air vent with 3/4 in. male NPT and 1/2 in. female NPT connections. It discharges large volumes of air during filling and start-up of a solar thermal circuit at pressures up to 150 psi (10 bar).
Specifications sourced from Caleffi technical brochure 01135/12 NA and installation instructions 28067.04. Last reviewed August 2026.
Key Features
Vents Against Full System Pressure
The DISCALAIR discharge mechanism, shared with the DISCAL 251 series separators, vents air at pressures up to 150 psi (10 bar) - twice the discharge pressure of the 250 series vent.
High-Capacity Air Discharge
Caleffi describes the DISCALAIR devices as discharging even large quantities of air formed in the circuits during the filling and start-up phase of a solar thermal system.
Rated to 320 deg F with Glycol
Working temperature range of -20 to 320 deg F (-30 to 160 deg C) with glycol solutions to 50 %, matching solar collector loop service conditions.
Dual NPT Connections
3/4 in. male NPT pipe connection with a 1/2 in. female NPT port. Caleffi specifies a maximum tightening torque of 25 ft-lb (35 N-m) on the 1/2 in. female NPT connection.
Corrosion-Resistant Internals
Chrome-plated brass EN 12165 CW617N body and cover, dezincification-resistant alloy stem, stainless steel float lever and spring, high-resistance polymer float.
Serviceable In Place
The top cover removes for access to the float mechanism, and the body separates from the section connected to the pipe for cleaning or inspection.
Technical Specifications
| Product Type | Solar Air Vent |
| Application | Closed solar thermal systems |
| Series | DISCALAIR / DISCAL SOLAR |
| Connections | 3/4 in. male NPT x 1/2 in. female NPT |
| Connection type | NPT |
| Medium | water, glycol solutions |
| Max. percentage of glycol | 50 % |
| Working temperature range | -20 to 320 deg F (-30 to 160 deg C) |
| Max. working pressure | 150 psi (10 bar) |
| Max. discharge pressure | 150 psi (10 bar) |
| Max. tightening torque, 1/2 in. F NPT connection | 25 ft-lb (35 N-m) |
| Dimensions | A 1/2 in.; B 4-1/2 in.; C 1-3/8 in.; D 2-1/8 in. (letters per dimension drawing in brochure 01135/12 NA) |
| Connection source note | connections follow the later instruction sheet 28067.04 (2020); the earlier brochure 01135/12 NA lists 1/2 in. F NPT only |
| Body and cover | brass EN 12165 CW617N, chrome plated |
| Float | high-resistance polymer |
| Float guide | brass EN 12164 CW614N |
| Stem | dezincification-resistant alloy EN 12164 CW602N |
| Float lever | stainless steel |
| Spring | stainless steel |
| Hydraulic seals | high-resistance elastomer |
| Manufacturer-listed weight | 1.3 lb |
Documentation
Related Products
- Caleffi NA29284 : Solar Air Vent Shut-Off Valve 1/2" FNPT x 1/2" MNPT
- Caleffi 250041A : Solar Automatic Air Vent 1/2" MNPT
- Caleffi 251003A : DISCAL Solar Air Separator 3/4"
- Caleffi 253040 : Solar Safety Relief Valve 150 psi
Frequently Asked Questions
What does Caleffi 251004A do?
It is a DISCALAIR high-performance automatic air vent that discharges large quantities of air during the filling and start-up of a solar thermal circuit, using the same discharge mechanism as the DISCAL 251 series air separators.
What connections does Caleffi 251004A have?
Per Caleffi instruction sheet 28067.04 (2020) the pipe connections are 3/4 in. male NPT and 1/2 in. female NPT, with a maximum tightening torque of 25 ft-lb (35 N-m) on the 1/2 in. female NPT connection. Note that the earlier technical brochure 01135/12 NA lists 1/2 in. F NPT only; this listing follows the later revision.
How does Caleffi 251004A differ from Caleffi 250041A?
Maximum discharge pressure. Caleffi rates the 251004A to vent air at up to 150 psi (10 bar); the 250041A is rated to 75 psi (5 bar). Caleffi describes the 251004A as discharging even large quantities of air during filling and start-up. Both brochures publish discharge capacity as a graph rather than a single rated figure.
Should Caleffi 251004A be left open in service?
Caleffi specifies that automatic air vents always be installed with a shut-off valve and isolated after the air has been removed during filling and commissioning.
What is the temperature rating of Caleffi 251004A?
Working temperature range is -20 to 320 deg F (-30 to 160 deg C), with water or glycol solutions up to 50 % concentration.
What is the warranty on Caleffi 251004A?
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 Vent
- Application:
- Solar Thermal
- Series:
- DISCALAIR
- Connection Type:
- NPT
- Connection Size:
- 3/4 in. x 1/2 in.
- Max Operating Pressure:
- 150 psi (10 bar)
- Max Discharge Pressure:
- 150 psi (10 bar)
- Medium Temperature Range:
- -20 to 320 deg F (-30 to 160 deg C)
- Max Glycol Concentration:
- 50 %
- Body Material:
- Brass, chrome plated
