Caleffi 551705 DISCAL 3/4 Inch Brass Deaerator Adjustable T

The 551705 is the DN 20 (3/4 inch) DISCAL deaerator with adjustable T-fitting from Caleffi. It removes air continuously from closed heating and chilled-water circuits down to micro-bubble level, and the rotatable T-fitting lets the same compact brass body be connected to horizontal or vertical pipes in tight plant rooms and fan-coil headers.

Why continuous deaeration matters

The datasheet explains that dissolved air comes out of solution whenever temperature rises or pressure falls: at a constant 2 bar absolute, heating water from 20 to 80 degrees C releases about 18 litres of air per cubic metre. Micro-bubbles form in boilers and in cavitation zones such as pump impellers and valve orifices. Left in the circuit, they cause noise, corrosion, localised overheating and mechanical damage. DISCAL separates them with concentric metal mesh surfaces that create a swirl so bubbles attach, grow and rise to a float-operated automatic air vent at the top.

Key features from the datasheet

• Removes all the air present in the system automatically, down to micro-bubble level; after 25 recirculations at the maximum recommended speed almost all the artificially released air is eliminated, as in the datasheet graph
• Float vent with a long chamber so impurities in the water do not reach the seal seat
• Maintenance without removing the device: unscrew the top cover to reach the moving parts; on this adjustable T version the body part with the vent is not removable
• 5517 series T-fitting is turned by hand to suit horizontal or vertical pipes
• Bi-directional flow on most models; on the 5517 adjustable version follow the arrow on the T-fitting
• Usable in heating and cooling circuits; hygroscopic safety cap 5620 recommended in places that cannot be inspected

Technical specification

Optional pre-formed PE-X shell insulation is mentioned for the threaded 551005 to 551009 drain models; the datasheet gives the PE-X insulation at 0 to 110 °C, class B2 (DIN 4102).

Selection and ordering guide

The 551 range runs from 3/4 inch compact bodies up to DN 300 flanged and weld-end units with insulation, covering terminal circuits to central plant.

Installation notes

• Install vertically, preferably after the boiler and on the pump suction side or upstream of the pump, where micro-bubble formation is highest.
• Keep the maximum recommended flow speed at the connections to about 1.2 m/s; the datasheet lists 22.7 l/min for this DN 20 size.
• On the adjustable T version turn the T-fitting by hand to the pipe direction, then tighten the locking nut.
• Position the device so that it can be reached for cleaning; if it cannot be inspected, replace the vent cap with the Caleffi 5620 hygroscopic safety cap.
• On flanged and weld-end sizes a cock releases large volumes of air during filling and removes floating impurities, and a lower plug can take a drain valve.

Applications in Gulf cooling and heating plants

Closed chilled-water loops in Oman and the GCC are filled and drained often during commissioning and shutdowns, so air is a standing problem for fan-coil units, air-handling coils and plate heat exchangers. The compact 551705 fits the secondary side of small plant such as packaged chillers, heat pump loops and boiler rooms, and the datasheet shows it in application diagrams with chillers, boilers and expansion vessels. The brass, 10 bar, 110 degree C duty is for building-services water systems, not process fluids.

Selection and installation notes

Hydronic components are selected from the design flow, the pressure drop and the maximum working pressure and temperature of the circuit. Check the connection size and thread type, fit isolating valves so the part can be serviced, flush the pipework before commissioning and respect the flow direction marked on the body. Insulate heating and chilled-water parts according to the project specification.

Information needed for a quotation

Send the full model code, the quantity, the delivery location in Oman or the GCC, the intended use and any accessories needed, so that the complete package can be quoted together.

Documents and supply information

The manufacturer data sheet is attached to this page and should be read together with the project specification and the site risk assessment before a purchase is confirmed. Ratings, standards and dimensions are quoted as printed on that sheet. Lead time, stock position and certificates available with the shipment are confirmed in the quotation, and we supply to Oman and the wider GCC region for industrial, utility and building services projects.

Related items

The datasheet names the Caleffi 5620 series hygroscopic safety cap as the replacement for the vent cap where the device cannot be inspected, and shows the deaerator in application diagrams with boilers, chillers, expansion vessels, strainers, safety relief valves and backflow preventers. Quote by exact code and confirm the connection type before ordering.

Related Caleffi products: Caleffi 546005 DISCALDIRT 3/4 Inch Deaerator and Dirt Separator, Caleffi 519500 3/4 Inch Adjustable Differential By-Pass Valve, Caleffi 548052 DN50 Flanged Hydraulic Separator PN16, Caleffi 132512 3/4 Inch Balancing Valve with Flow Meter, Caleffi 521400 1/2 Inch Anti-Scale Thermostatic Mixing Valve and Caleffi 140340 DN15 Differential Pressure Regulating Valve.

Documents and quotation

The official Caleffi DISCAL 551 series datasheet 01060/17 GB (2017) is linked on this page. Send the code, quantity and circuit data to request a quotation. See more in Hydraulic Valves & Components.