SP-3 is a 3-liter (0.8 gallon) expansion vessel designed for closed-loop solar hot water systems. It effectively manages temperature fluctuations to maintain safe pressure levels and protect the system from excessive variations.
Built for extreme environments, the tank supports up to 10 bar (150 psi) and 130°C (266°F). It is factory pre-charged to 3.5 bar (50 psi) with 100% nitrogen gas to ensure stable performance and prevent thermal pressure spikes.
With a compact 14.0 cm diameter, the SP-3 is ideal for point-of-use installations. It supports thermal expansion for water heaters up to 50 gallons, providing a reliable, space-saving solution for solar applications.
Product Overview
The SP-3 is a 3-liter (0.8 gallon) diaphragm tank designed specifically to protect closed-loop solar thermal systems. It manages the expansion of water-glycol mixtures, preventing high pressure buildup during peak sun exposure and maintaining system stability when temperatures drop below freezing.
Constructed with a heavy-duty cold-rolled steel shell and a Red (RAL 3011) epoxy finish, the tank offers excellent rust resistance. Inside, a high-temperature liner and a premium EPDM diaphragm (DIN 4807) are engineered to withstand the intense heat and chemical additives typical of solar-thermal loops.
Featuring a 1" 304 stainless steel connector, the CE and ISO 9001 certified SP-3 ensures a lead-free and secure connection. This professional-grade vessel provides a reliable, long-lasting solution for ensuring the safety and efficiency of demanding solar applications.
Certification
Specifications and Technical Data
| Parameter | Value |
| Model Number | SP-3 |
| Total Tank Volume | 3 liters / 0.8 gallons |
| Diameter | 14 cm / 5.5 inch |
| Height | 21 cm / 8.3 inch |
| Net Weight (NW) |
4.1 kg / 9.0 lbs. * |
| Gross Weight (GW) | 4.7 kg / 10.4 lbs. * |
| Shipping Volume | 0.81 CUF * |
| Operating Temperature | 1 - 130°C / 34 - 266°F |
| Factory Pre-charge | 3.5 bar | 50 psi |
| Max. Operating Pressure | 10 bar | 150 psi |
| Connection | 1” NPT / BSPT Stainless Steel |
| Liner Material | Polypropylene |
| Diaphragm Material | EPDM Rubber |
| Shell | Cold Rolled Carbon Steel |
| External Coating | Triple Grade Blue Paint |
| Pre-charge Gas | 100% Nitrogen |
* SP-3 is packed 4 pcs per box
Key Features & Design Advantages
How the Solar-Plus Pressure Tank Works
In closed-loop solar systems, the heat transfer fluid (often a water/glycol mix) expands significantly as it absorbs intense heat from solar collectors. The SP-3 manages this by storing the expanded fluid against the high-temperature EPDM rubber diaphragm, pushing against the nitrogen-filled air cushion. This safely relieves pressure. When the system cools—such as at night or in freezing temperatures—the nitrogen cushion forces the fluid back into the pipes, preventing the pressure from dropping dangerously low
Key benefits
Typical Applications
Frequently Asked Question (FAQ)
A: Yes, the SP-3 is specifically designed for 50-gallon solar water heaters, offering a highly compact 3-liter (0.8-gallon) capacity.
A: Because of its compact size, the SP-3 is packaged and shipped conveniently with 4 pieces per standard box.
A: Absolutely. It features an EPDM rubber membrane with a high-temperature heat resistance liner that safely handles maximum working temperatures up to 130°C (266°F).