The Caleffi 253040 is a TUV-certified diaphragm safety relief valve for closed solar thermal systems, factory preset to 10 bar (150 psi) with 1/2 in. female inlet and 3/4 in. female outlet connections. It discharges collector-loop fluid to atmosphere before system pressure can exceed the design limit of the collectors and connected equipment.
Specifications sourced from Caleffi technical brochure 01089 NA, installation instructions 28035.06 and catalog 03288 EN. Last reviewed August 2026.
Key Features
Preset to 10 bar (150 psi)
Factory calibrated and sealed at 10 bar (150 psi). The setting is marked on the tamper-proof plate in the control knob, so the calibration can be verified without removing the valve.
TUV Certified for Solar Service
Approved to TRD 721 and VdTUV standard SV 100 section 7.7 for solar heating systems, ID 0000013604. TUV Rheinland is a U.S. Nationally Recognized Testing Laboratory.
171,000 BTU/h Discharge Capacity
Rated for 171,000 BTU/h (50 kW) across the 25304_ codes, with 10 % opening overpressure and 20 % closing differential. The outlet is oversized relative to the inlet to pass the volume.
Rated for 50 % Glycol
Medium is water or glycol solution to 50 % concentration, the antifreeze range used in freeze-protected collector arrays. The disk seal uses a high-resistance elastomer chosen for hot glycol service.
Chrome-Plated Brass Body
Brass EN 12165 CW617N with chrome plating to resist dirt and moisture in outdoor collector installations. The knob is PA6G30 polyamide, selected for heat and UV resistance.
PED Category IV
Built to the essential safety requirements of Pressure Equipment Directive 2014/68/EU, PED category IV, and to the UK Pressure Equipment (Safety) Regulations SI 2016 No. 1105.
Technical Specifications
| Product Type | Solar safety relief valve (diaphragm) |
| Application | Closed solar thermal systems |
| Series | 253 |
| Relief pressure setting | 10 bar (150 psi) |
| Connections | 1/2 in. F x 3/4 in. F |
| Connection type | Threaded, female inlet x female outlet |
| Nominal pressure | PN 10 - 150 psi (10 bar) |
| Medium | water, glycol solutions |
| Max. percentage of glycol | 50 % |
| Working temperature range | -30 to 160 deg C (-22 to 320 deg F) |
| Discharge capacity | 171,000 BTU/h (50 kW) - 25304_ codes, 1/2 in. inlet |
| Opening overpressure | 10 % |
| Closing differential | 20 % |
| PED category | IV |
| Approval | TUV to TRD 721 / SV 100 section 7.7, ID 0000013604 |
| Body material | brass EN 12165 CW617N, chrome plated |
| Control spindle | brass |
| Relief seal | high-resistance elastomer |
| Spring | stainless steel |
| Control knob | PA6G30 polyamide |
| Dimensions | A 1/2 in.; B 3/4 in.; C 1 in.; D 2-3/4 in.; E 1-3/8 in. (letters per dimension drawing in brochure 01089 NA) |
| Manufacturer-listed weight | 0.3 lb |
Documentation
Related Products
- Caleffi 253042 : Solar Safety Relief Valve 36 psi
- Caleffi 253043 : Solar Safety Relief Valve 45 psi
- Caleffi 253044 : Solar Safety Relief Valve 60 psi
- Caleffi 253046 : Solar Safety Relief Valve 90 psi
Frequently Asked Questions
What pressure does Caleffi 253040 relieve at?
Caleffi 253040 is factory preset to 10 bar (150 psi). It opens with a 10 % overpressure and reseats within a 20 % closing differential, and is rated for a discharge capacity of 171,000 BTU/h (50 kW).
Is the discharge rating of Caleffi 253040 40 kW or 50 kW?
50 kW (171,000 BTU/h). The 40 kW figure in installation instructions 28035.06 applies to the 25364_ codes, which have a 1/2 in. outlet. The 25304_ codes covered here have a 3/4 in. outlet and are rated 50 kW; the 25305_ codes are rated 100 kW. Technical brochure 01089 NA and catalog 03288 both list 50 kW for this size.
Can Caleffi 253040 be used with glycol?
Yes. The 253 series is rated for water and glycol solutions up to 50 % concentration and uses a high-resistance elastomer disk seal specifically selected for hot glycol service in solar collector loops.
What is the temperature rating of Caleffi 253040?
The working temperature range is -30 to 160 deg C (-22 to 320 deg F) per Caleffi installation instructions 28035.06 and catalog 03288 EN. Note that Caleffi technical brochure 01089 NA lists -20 to 360 deg F (-30 to 180 deg C) for this series; confirm with Caleffi North America for applications near the limit.
Where should Caleffi 253040 be installed?
Caleffi specifies installation near the point where the circuit is filled and upstream of the expansion tank, in the coolest part of the solar loop, with no shut-off device between the valve and the system. Mount vertically in line with the flow arrow. The connecting pipe should be no more than 1 m long with no bends.
Does Caleffi 253040 need a discharge pipe?
Yes. A discharge pipe must be fitted and routed to a suitable container or air gap, terminating roughly 12 in. (305 mm) above it. Maximum discharge pipe length is 2 m with no more than two bends. The vent opening must never be plugged.
What is the warranty on Caleffi 253040?
Caleffi North America covers this product under its two-year limited warranty against defects in material and workmanship from the date of shipment. ZOT Supply is an authorized Caleffi distributor.
- Product Type:
- Solar Safety Relief Valve
- Application:
- Solar Thermal
- Series:
- 253
- Relief Pressure Setting:
- 10 bar (150 psi)
- Connection Type:
- Threaded
- Connection Size:
- 1/2 in. x 3/4 in.
- Max Operating Pressure:
- 150 psi (10 bar)
- Medium Temperature Range:
- -30 to 160 deg C (-22 to 320 deg F)
- Max Glycol Concentration:
- 50 %
- Body Material:
- Brass, chrome plated
