The Belimo ZONE320S-35+ZONE24NC-S is a zone valve assembly: the ZONE320S-35, a forged brass, 3-way on/off diverting zone valve with 3/4" sweat ends: Cv 3.5, 30 psi close-off, 300 psi body pressure rating and ANSI Class III 0.1% leakage, for chilled or hot water up to 50% glycol, fitted with the ZONE24NC-S spring return fail-safe actuator for 2-wire on/off control at AC 24 V. A built-in auxiliary switch is rated 1 x SPST, 0.4 A resistive (0.4 A inductive) @ AC 24 V.
Typically used on fan coil units, baseboards and other hydronic applications where fail-safe operation on 2-wire control is required, in systems with variable or constant flow. The compact body and actuator fit tight spaces where on/off control is needed.
Specifications per Belimo ZONE320S-35 technical data sheet 2023-01-10; ZONE320S-35+ZONE24NC-S assembly data sheet (ZONE320S-35 and ZONE24NC-S pages, 2022-01-12). Reviewed 2026-10-09.
Best For
- Fan coil units, baseboards and other hydronic terminal units
- On/off diverting duty in hydronic systems with variable or constant flow
- Soldered piping with 3/4" sweat ends
- 24 V thermostat circuits (7 VA, class 2 power source)
- Switching an auxiliary circuit from the built-in SPST switch
Warranty
Belimo covers the ZONE320S-35 valve and the ZONE24NC-S actuator each with a 2-year warranty.
Key Features
3-way on/off diverting
Flow pattern 3-way, on/off diverting flow characteristic, ANSI Class III 0.1% leakage, Cv 3.5.
30 psi close-off
Close-off pressure 30 psi with a 300 psi body pressure rating.
Spring return fail-safe
Spring return actuator for fail-safe operation on 2-wire on/off control.
AC 24 V supply
AC 24 V, 50/60 Hz; 6.5 W in operation, transformer sizing 7 VA (class 2 power source).
Built-in auxiliary switch
1 x SPST, 0.4 A resistive (0.4 A inductive) @ AC 24 V, wired on separate red leads to the auxiliary circuit.
3/4" Sweat connection
3/4" sweat ends; actuator connects by 18 in. wire leads.
ZOT Supply is an authorized distributor of Belimo products.
Technical Specifications
Valve: Belimo ZONE320S-35
| Valve model | Belimo ZONE320S-35 |
| Valve size | 0.75 in. [DN 20] |
| Flow pattern | 3-way |
| Flow characteristic | on/off, diverting |
| Cv | 3.5 |
| Close-off pressure | 30 psi |
| Body pressure rating | 300 psi |
| Leakage rate | ANSI Class III 0.1% |
| Fluid | chilled or hot water, up to 50% glycol |
| Fluid temperature range (water) | 32...212°F [0...100°C] |
| Pipe connection | sweat |
| Valve body | forged brass |
| Housing seal | EPDM |
| Stem | stainless steel |
| Seat | EPDM |
| Suitable actuators | ZONE (spring) |
| Dimensions A / B / C / D / E / F | 4.0 in. [102 mm] / 2.8 in. [70 mm] / 3.5 in. [89 mm] / 5.0 in. [127 mm] / 1.2 in. [30 mm] / 1.2 in. [31 mm] |
Actuator: Belimo ZONE24NC-S
| Actuator model | Belimo ZONE24NC-S |
| Nominal voltage | AC 24 V |
| Nominal voltage frequency | 50/60 Hz |
| Power consumption in operation | 6.5 W |
| Transformer sizing | 7 VA (class 2 power source) |
| Auxiliary switch | 1 x SPST, 0.4 A resistive (0.4 A inductive) @ AC 24 V |
| Electrical connection | 18 in. wire leads |
| Manual override | hand lever |
| Angle of rotation | 90° |
| Noise level, motor | 35 dB(A) |
| Noise level, fail-safe | 35 dB(A) |
| Position indication | Mechanically (integrated) |
| Degree of protection IEC/EN | IP20 |
| Degree of protection NEMA/UL | NEMA 1 |
| Enclosure | UL Enclosure Type 1 |
| Agency listing | CE, cULus |
| Quality standard | ISO 9001 |
| Ambient temperature | 32...104°F [0...40°C] |
| Storage temperature | -40...176°F [-40...80°C] |
| Ambient humidity | Max. 95% RH, non-condensing |
| Servicing | maintenance-free |
| Housing material | galvanized steel |
| Grounding | Meets cULus requirements without the need of an electrical ground connection |
Documentation
FAQ
What is the Cv and close-off pressure of the Belimo ZONE320S-35+ZONE24NC-S?
Cv 3.5 with a 30 psi close-off pressure and a 300 psi body pressure rating.
Is the ZONE320S-35+ZONE24NC-S a 2-way or 3-way valve?
3-way. The flow characteristic is on/off, diverting, with ANSI Class III 0.1% leakage.
How is the ZONE320S-35+ZONE24NC-S wired?
Two wires: the thermostat switches L1 (hot) to one black actuator lead and L2 connects to the other. The auxiliary switch is on the two red leads.
What is the auxiliary switch rating on the ZONE320S-35+ZONE24NC-S?
1 x SPST, 0.4 A resistive (0.4 A inductive) @ AC 24 V.
What power supply does the ZONE320S-35+ZONE24NC-S need?
AC 24 V, 50/60 Hz. Power consumption is 6.5 W in operation and transformer sizing is 7 VA (class 2 power source).
What fluids can the ZONE320S-35+ZONE24NC-S control?
Chilled or hot water, up to 50% glycol, at fluid temperatures of 32...212°F [0...100°C].
- Valve Pattern:
- 3-Way
- Valve Size:
- 3/4 Inch
- Connection Type:
- Sweat
- CV Rating:
- 3.5
- Max Close-Off Pressure:
- 30 psi
- Max Operating Pressure:
- 300 psi
- Medium Temperature Range:
- 32-212 °F
- Body Material:
- Forged Brass
- Actuator Type:
- Fail-Safe
- Voltage:
- 24VAC
- Control Signal:
- On/Off
- Auxillary Switch:
- (1) SPST 0.4A @ 24VAC
- Power Connection:
- Wire Leads
