How to Choose a Hydraulic Separator for Your Boiler Room
A hydraulic separator decouples the boiler circuit from the consumer circuits and protects the boiler from thermal shock. We explain the operating principle and how to select the right Termojet ГС model by capacity — without overspending or making mistakes.
The hydraulic separator — one of the most underrated components in any boiler room. It is invisible during operation, yet it determines whether a multi-circuit system runs stably. Let us break down the principle and provide a clear selection algorithm.
Why You Need a Hydraulic Separator
In a modern boiler room there is almost always more than one pump: one on the boiler, separate ones for radiators, underfloor heating, and the domestic hot water cylinder. When they all work on a shared network, they compete for flow. The boiler may receive insufficient coolant and overheat, while remote circuits remain underheated.
The hydraulic separator creates a low-resistance zone where the boiler flow and consumer flows meet without interfering with each other. The boiler receives a stable flow rate regardless of how many circuits are open. In simple terms — it hydraulically decouples the primary (boiler) circuit from the secondary circuits.
What This Means in Practice
- Stable flow through the boiler — no thermal shock or short-cycling.
- Protection of circulation pump impellers from hydraulic conflicts.
- If the unit has top/bottom connections, it simultaneously removes air and sludge, combining the functions of a separator.
Sizing by Capacity — the Key Criterion
The hydraulic separator must be sized by the maximum total coolant flow rate, not by guesswork. Approximate ranges for ΔT=20 °C:
- ГС-25 (1") — boiler rooms up to approximately 50 kW
- ГС-26 (1¼") — up to ~90 kW
- ГС-27 (1½") — up to ~130 kW
- ГС-28 (2") — up to ~170 kW
- Flanged ГС-30 and the ГС-31…34 series — for boiler rooms from 200 kW and industrial applications
Material and Design
Termojet standard: steel in removable XPE thermal insulation, which reduces heat losses and condensation. For higher capacities — flanged models with a base frame.
When a Hydraulic Separator Is NOT Needed
- A single boiler with a single circuit at identical flow rates.
- Systems with a heat pump and a buffer tank — the buffer itself typically performs the decoupling function.
Common Mistakes
1. Sizing by pipe diameter rather than flow rate.
2. No automatic air vent and no drain valve for sludge removal.
3. Installation without thermal insulation — unnecessary heat losses.
4. Using a separator where a thermo-hydraulic distributor (combining separator and manifold) would suffice.
Summary
A correctly sized hydraulic separator is relatively inexpensive but saves the boiler and pumps from premature wear. The Termojet ГС range covers models from 1" to industrial flanged versions — with thermal insulation and ready to install.
