Adjustment tees

Control tees are manual restrictors most often placed on the return lines of emitters (radiators, underfloor heating loops via manifolds, fan coil units) to regulate flow and balance a heating/cooling system. Their function is to limit excess flow in nearby circuits, guarantee minimum flow in distant circuits, stabilize the temperature difference (ΔT), and prevent noise and temperature fluctuations. A control tee is more than just a "valve": its Kv value, stroke length, pre-set position, and available pressure difference (ΔP) all determine the accuracy of the balancing.

Adjustment tees: role, installation and fine-tuning

An adjustment tee has a seat and a needle valve (or check valve) allowing for fine adjustment. It is installed:

- On the return of each terminal, arrow in the direction of the flow.

- With front access for reading/adjusting the preset (numbered markers).

- On clean networks (sludge removal, upstream screen filter) to avoid seat erosion.

- With, if possible, pressure tapping points (or dedicated measuring valve) in order to control the flow rate by the ΔP/Kv method.

- Typical setup : after flushing and purging, the calculated presets are applied (table per transmitter), then the ΔT and/or flow rate are checked. On variable flow networks (2-way valves + VFD pumps), tees define the hydraulic floor of each branch; on constant flow or older networks, they prevent chronic overflows. They can also serve as isolation points for maintenance (with a plug/shut-off).

Advantages, limitations and points to consider regarding adjusting tees

Interests

• Uniform comfort: each emitter receives its flow rate, eliminating lukewarm zones.
• Silence: excessive overflows and ΔP limited → whistling reduced.
• Efficiency: ΔT maintained → more efficient condensing boilers and heat pumps.
• Maintenance: pre-setting reference points → reproducible interventions.

Boundaries

• Limited measurement: without sockets, we guess more than we measure (favor models with measurable connections or balancing valves).
• Sensitive to sludge: needle/seat can seize → plan for sludge removal and filters.
• Low authority if Kvs is too high: unstable "quarter-turn" adjustment.
• Not “dynamic”: PICVs (pressure-independent valves) handle ΔP variations better.

Points to consider

• Sizing: choose a Kv consistent with the computing throughput and the available ΔP (avoid "too big").
• Documentation: establish a table of presets (position, target ΔT, flow rates), to be integrated into the DOE.
• Water quality: prior descaling, inhibitor, conductivity control; upstream sieve filter.
• GTB/VFD: place the ΔP sensor at the critical point; apply a pressure reset to limit noise when closing.
• Thermal insulation: treat the clarinet and the returns to maintain the measured ΔT.
• Access: orientation allowing reading/adjustment without dismantling the furniture or the covers.

Anecdote — “The radiators finally agree in Bordeaux”

In Bordeaux, an office building experienced alternating between overheated offices near the riser and chilly surrounding areas. The regulating tees were fully open, some were seized, and no pre-setting records existed. The team flushed the system, replaced the blocked tees with models featuring pressure taps, calculated the flow rates per radiator, and completed a control table. With a ΔP reset on the VFD pump, the ΔT returned to its nominal value, the whistling noises stopped, and the floors finally had a uniform temperature. The building manager noted: "A quarter turn in the right place is better than an extra degree of setpoint."