Flamco Flexvent Automatic Air Vent with Shut-Off Valve – 27740 (½" BSP) and 27750 (⅜" BSP)
The Flamco Flexvent is a compact, float-operated automatic air vent for sealed heating and cooling systems. A proven design with decades of market use, it continuously vents trapped air from the highest points of a system without manual intervention — preventing corrosion, noisy pipework, cold spots in radiators, and reduced heat transfer efficiency. The brass body contains an all-plastic interior mechanism: when air collects in the housing the float drops, opening the vent valve to release the air; once the air is expelled the rising water level lifts the float closed again.
Both variants include an integrated shut-off valve, allowing the vent to be isolated and removed for maintenance without draining the system. The ½" and ⅜" versions share the same 30mm diameter body — connection size is the only difference. A captive cap with open/close function prevents leaks when the vent is closed, and the self-sealing notched gasket on the valve sleeve means no PTFE tape or thread sealant is required during installation. All Flexvents are individually tested at the factory before dispatch. Compatible with glycol-based antifreeze at concentrations up to 50%.
Variant Specifications
| Parameter | 27740 — Flexvent ½" | 27750 — Flexvent ⅜" |
|---|---|---|
| MPN | 27740 | 27750 |
| GTIN | — | 08712874277502 |
| Connection | R½" male — BSPT (ISO 7-1) | R⅜" male — BSPT (ISO 7-1) |
| Outer pipe diameter | 21.3mm | 17.2mm |
| Body diameter (Ø) | 30mm | 30mm |
| Height (H) | 75.5mm | 78mm |
| Weight | approx. 0.11 kg | 0.108 kg |
| Packaging (H × W × L) | — | 112 × 39 × 39mm |
| Shut-off valve | Yes | Yes |
| Min working temperature | -10°C | -10°C |
| Max working temperature (continuous) | 90°C | 90°C |
| Max temperature (peak load) | 120°C | 120°C |
| Min working pressure | 0.2 Bar | 0.2 Bar |
| Max working pressure | 6.0 Bar | 6.0 Bar |
| Max pressure (peak load) | 10.0 Bar | 10.0 Bar |
| Glycol compatibility | Up to 50% concentration | Up to 50% concentration |
| Housing material | Brass | Brass |
| Internal mechanism | All plastic float mechanism | All plastic float mechanism |
| Suitable for | Heating, cooling, closed systems | Heating, cooling, closed systems |
| Manufacturer | Flamco BV (Aalberts NV), Netherlands | |
The ½" (27740) is the standard choice for most heating system tappings and boiler flow headers. The ⅜" (27750) is used where the tapping or fitting calls for a smaller connection — common on older radiator valve bodies, some boiler air vent bosses, and branch tees with ⅜" female sockets. Both share the same body diameter and mechanism.
Key Features
Float-operated — fully automatic
The all-plastic float mechanism operates entirely by the water level in the housing. No servicing, adjusting, or manual operation is required during normal system running. The substantial distance between water and the closing mechanism reduces contamination risk, and the large air cushion at the top of the housing prevents the valve seat from being wetted by system debris.
Integrated shut-off valve
The built-in valve sleeve allows the vent to be isolated from system pressure without draining — the vent can be removed, inspected, or replaced during maintenance while the system stays pressurised. The valve sleeve threads include a self-sealing notched gasket — no PTFE tape or jointing compound is needed on installation.
Captive cap — leak prevention
The captive (retained) top cap cannot be removed or lost — it stays attached to the body. In the closed position it seals the vent port with integral expansion sealing rings, preventing drips during system pressurisation and when the vent is screwed fully closed. In the open position the cap allows free air discharge.
Glycol compatible — heat pump & solar ready
Compatible with glycol-based antifreeze at concentrations up to 50% — making the Flexvent suitable for air source heat pump external circuits, ground source brine circuits, solar thermal primary circuits, and any other closed system where glycol is used for freeze protection. Rated to -10°C working temperature with peak load tolerance to 120°C.
Compact — 30mm body, fits anywhere
Both variants share a 30mm body diameter and under 80mm height — small enough to fit in boiler cabinets, on pipework headers, at the top of micro-bore manifolds, and in any tight space where air typically collects. Flamco has designed the Flexvent range to be easy to install in any orientation of the connected pipework.
Factory tested — individually
Every Flexvent is tested at the Flamco factory before leaving — not batch tested or sample tested. This gives confidence that each unit will perform correctly on installation. Flamco has manufactured automatic air vents since 1956 and the Flexvent is one of the most widely specified and trusted designs in the European heating industry.
Flamco Flexvent 27740 ½" (single) | Flamco Flexvent 27750 ⅜" (single) | Flamco Flexvent Box of 50 (27740) | Intatec IntaKlean HP Magnetic Filter | Sentinel X100 System Inhibitor | Flamco Fill & Drain Valve | Boiler Tapping ½" Female Boss
Flamco Flexvent Automatic Air Vent with Shut-Off Valve – 27740 (½" BSP) and 27750 (⅜" BSP)
The Flamco Flexvent is a compact, float-operated automatic air vent for sealed heating and cooling systems. A proven design with decades of market use, it continuously vents trapped air from the highest points of a system without manual intervention — preventing corrosion, noisy pipework, cold spots in radiators, and reduced heat transfer efficiency. The brass body contains an all-plastic interior mechanism: when air collects in the housing the float drops, opening the vent valve to release the air; once the air is expelled the rising water level lifts the float closed again.
Both variants include an integrated shut-off valve, allowing the vent to be isolated and removed for maintenance without draining the system. The ½" and ⅜" versions share the same 30mm diameter body — connection size is the only difference. A captive cap with open/close function prevents leaks when the vent is closed, and the self-sealing notched gasket on the valve sleeve means no PTFE tape or thread sealant is required during installation. All Flexvents are individually tested at the factory before dispatch. Compatible with glycol-based antifreeze at concentrations up to 50%.
Variant Specifications
| Parameter | 27740 — Flexvent ½" | 27750 — Flexvent ⅜" |
|---|---|---|
| MPN | 27740 | 27750 |
| GTIN | — | 08712874277502 |
| Connection | R½" male — BSPT (ISO 7-1) | R⅜" male — BSPT (ISO 7-1) |
| Outer pipe diameter | 21.3mm | 17.2mm |
| Body diameter (Ø) | 30mm | 30mm |
| Height (H) | 75.5mm | 78mm |
| Weight | approx. 0.11 kg | 0.108 kg |
| Packaging (H × W × L) | — | 112 × 39 × 39mm |
| Shut-off valve | Yes | Yes |
| Min working temperature | -10°C | -10°C |
| Max working temperature (continuous) | 90°C | 90°C |
| Max temperature (peak load) | 120°C | 120°C |
| Min working pressure | 0.2 Bar | 0.2 Bar |
| Max working pressure | 6.0 Bar | 6.0 Bar |
| Max pressure (peak load) | 10.0 Bar | 10.0 Bar |
| Glycol compatibility | Up to 50% concentration | Up to 50% concentration |
| Housing material | Brass | Brass |
| Internal mechanism | All plastic float mechanism | All plastic float mechanism |
| Suitable for | Heating, cooling, closed systems | Heating, cooling, closed systems |
| Manufacturer | Flamco BV (Aalberts NV), Netherlands | |
The ½" (27740) is the standard choice for most heating system tappings and boiler flow headers. The ⅜" (27750) is used where the tapping or fitting calls for a smaller connection — common on older radiator valve bodies, some boiler air vent bosses, and branch tees with ⅜" female sockets. Both share the same body diameter and mechanism.
Key Features
Float-operated — fully automatic
The all-plastic float mechanism operates entirely by the water level in the housing. No servicing, adjusting, or manual operation is required during normal system running. The substantial distance between water and the closing mechanism reduces contamination risk, and the large air cushion at the top of the housing prevents the valve seat from being wetted by system debris.
Integrated shut-off valve
The built-in valve sleeve allows the vent to be isolated from system pressure without draining — the vent can be removed, inspected, or replaced during maintenance while the system stays pressurised. The valve sleeve threads include a self-sealing notched gasket — no PTFE tape or jointing compound is needed on installation.
Captive cap — leak prevention
The captive (retained) top cap cannot be removed or lost — it stays attached to the body. In the closed position it seals the vent port with integral expansion sealing rings, preventing drips during system pressurisation and when the vent is screwed fully closed. In the open position the cap allows free air discharge.
Glycol compatible — heat pump & solar ready
Compatible with glycol-based antifreeze at concentrations up to 50% — making the Flexvent suitable for air source heat pump external circuits, ground source brine circuits, solar thermal primary circuits, and any other closed system where glycol is used for freeze protection. Rated to -10°C working temperature with peak load tolerance to 120°C.
Compact — 30mm body, fits anywhere
Both variants share a 30mm body diameter and under 80mm height — small enough to fit in boiler cabinets, on pipework headers, at the top of micro-bore manifolds, and in any tight space where air typically collects. Flamco has designed the Flexvent range to be easy to install in any orientation of the connected pipework.
Factory tested — individually
Every Flexvent is tested at the Flamco factory before leaving — not batch tested or sample tested. This gives confidence that each unit will perform correctly on installation. Flamco has manufactured automatic air vents since 1956 and the Flexvent is one of the most widely specified and trusted designs in the European heating industry.
Flamco Flexvent 27740 ½" (single) | Flamco Flexvent 27750 ⅜" (single) | Flamco Flexvent Box of 50 (27740) | Intatec IntaKlean HP Magnetic Filter | Sentinel X100 System Inhibitor | Flamco Fill & Drain Valve | Boiler Tapping ½" Female Boss
Product Information
Product Information
Shipping & Returns
Shipping & Returns
Description
The Flamco Flexvent is a compact, float-operated automatic air vent for sealed heating and cooling systems. A proven design with decades of market use, it continuously vents trapped air from the highest points of a system without manual intervention — preventing corrosion, noisy pipework, cold spots in radiators, and reduced heat transfer efficiency. The brass body contains an all-plastic interior mechanism: when air collects in the housing the float drops, opening the vent valve to release the air; once the air is expelled the rising water level lifts the float closed again.
Both variants include an integrated shut-off valve, allowing the vent to be isolated and removed for maintenance without draining the system. The ½" and ⅜" versions share the same 30mm diameter body — connection size is the only difference. A captive cap with open/close function prevents leaks when the vent is closed, and the self-sealing notched gasket on the valve sleeve means no PTFE tape or thread sealant is required during installation. All Flexvents are individually tested at the factory before dispatch. Compatible with glycol-based antifreeze at concentrations up to 50%.
Variant Specifications
| Parameter | 27740 — Flexvent ½" | 27750 — Flexvent ⅜" |
|---|---|---|
| MPN | 27740 | 27750 |
| GTIN | — | 08712874277502 |
| Connection | R½" male — BSPT (ISO 7-1) | R⅜" male — BSPT (ISO 7-1) |
| Outer pipe diameter | 21.3mm | 17.2mm |
| Body diameter (Ø) | 30mm | 30mm |
| Height (H) | 75.5mm | 78mm |
| Weight | approx. 0.11 kg | 0.108 kg |
| Packaging (H × W × L) | — | 112 × 39 × 39mm |
| Shut-off valve | Yes | Yes |
| Min working temperature | -10°C | -10°C |
| Max working temperature (continuous) | 90°C | 90°C |
| Max temperature (peak load) | 120°C | 120°C |
| Min working pressure | 0.2 Bar | 0.2 Bar |
| Max working pressure | 6.0 Bar | 6.0 Bar |
| Max pressure (peak load) | 10.0 Bar | 10.0 Bar |
| Glycol compatibility | Up to 50% concentration | Up to 50% concentration |
| Housing material | Brass | Brass |
| Internal mechanism | All plastic float mechanism | All plastic float mechanism |
| Suitable for | Heating, cooling, closed systems | Heating, cooling, closed systems |
| Manufacturer | Flamco BV (Aalberts NV), Netherlands | |
The ½" (27740) is the standard choice for most heating system tappings and boiler flow headers. The ⅜" (27750) is used where the tapping or fitting calls for a smaller connection — common on older radiator valve bodies, some boiler air vent bosses, and branch tees with ⅜" female sockets. Both share the same body diameter and mechanism.
Key Features
Float-operated — fully automatic
The all-plastic float mechanism operates entirely by the water level in the housing. No servicing, adjusting, or manual operation is required during normal system running. The substantial distance between water and the closing mechanism reduces contamination risk, and the large air cushion at the top of the housing prevents the valve seat from being wetted by system debris.
Integrated shut-off valve
The built-in valve sleeve allows the vent to be isolated from system pressure without draining — the vent can be removed, inspected, or replaced during maintenance while the system stays pressurised. The valve sleeve threads include a self-sealing notched gasket — no PTFE tape or jointing compound is needed on installation.
Captive cap — leak prevention
The captive (retained) top cap cannot be removed or lost — it stays attached to the body. In the closed position it seals the vent port with integral expansion sealing rings, preventing drips during system pressurisation and when the vent is screwed fully closed. In the open position the cap allows free air discharge.
Glycol compatible — heat pump & solar ready
Compatible with glycol-based antifreeze at concentrations up to 50% — making the Flexvent suitable for air source heat pump external circuits, ground source brine circuits, solar thermal primary circuits, and any other closed system where glycol is used for freeze protection. Rated to -10°C working temperature with peak load tolerance to 120°C.
Compact — 30mm body, fits anywhere
Both variants share a 30mm body diameter and under 80mm height — small enough to fit in boiler cabinets, on pipework headers, at the top of micro-bore manifolds, and in any tight space where air typically collects. Flamco has designed the Flexvent range to be easy to install in any orientation of the connected pipework.
Factory tested — individually
Every Flexvent is tested at the Flamco factory before leaving — not batch tested or sample tested. This gives confidence that each unit will perform correctly on installation. Flamco has manufactured automatic air vents since 1956 and the Flexvent is one of the most widely specified and trusted designs in the European heating industry.
Flamco Flexvent 27740 ½" (single) | Flamco Flexvent 27750 ⅜" (single) | Flamco Flexvent Box of 50 (27740) | Intatec IntaKlean HP Magnetic Filter | Sentinel X100 System Inhibitor | Flamco Fill & Drain Valve | Boiler Tapping ½" Female Boss
