SP-18 is an 18-liter (4.5 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 28.0 cm diameter, the SP-18 is ideal for point-of-use installations. It supports thermal expansion for water heaters up to 90 gallons, providing a reliable, space-saving solution for solar applications.
Product Overview
The SP-18 is an 18-liter (4.5 gallon) diaphragm expansion tank specifically engineered for larger solar thermal installations. It manages the significant expansion of water-glycol mixtures, preventing over-pressure during stagnant peak heating and maintaining system equilibrium when temperatures fall below freezing.
The tank features a heavy-duty cold-rolled steel shell with a Red (RAL 3011) epoxy powder coating for superior oxidation resistance. Inside, a high-temperature resistant liner and a premium EPDM diaphragm (DIN 4807) are designed to withstand the intense thermal cycles and chemical additives typical of demanding solar-thermal loops.
Equipped with a 1" 304 stainless steel connector, the CE and ISO9001 certified SP-18 ensures a lead-free and perfectly secure connection. This professional-grade vessel provides a high-capacity, reliable solution for protecting solar collectors and ensuring the long-term efficiency of the entire system.
Certification
Specifications and Technical Data
| Parameter | Value |
| Model Number | SP-18 |
| Total Tank Volume | 18 liters / 4.5 gallons |
| Diameter | 28.0 cm / 11 inch |
| Height | 36.5 cm / 14.4 inch |
| Net Weight (NW) | 3.4 kg / 7.5 lbs. |
| Gross Weight (GW) | 3.8 kg / 8.4 lbs. |
| Shipping Volume | 1.08 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 |
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-18 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: To determine if the SP-18 is the correct size for your solar installation, you need to check the total capacity of your solar water heater. The SP-18 provides 18 liters (4.5 gallons) of expansion volume and is specifically sized to support a 90-gallon water heater.
It is engineered to safely handle thermal liquid expansion (typically a mixture of water and glycol) in solar hot water systems and solar evacuated tubes that reach extreme temperatures up to 130°C (266°F).
A: Standard expansion tanks are often rated only for domestic hot water. The SP-18 uses a specialized EPDM rubber compliant with DIN 4807 standards, which is formulated to resist the chemical breakdown and hardening that occurs when exposed to high-temperature solar fluids and antifreeze.
A : Yes. The combination of a cold-rolled carbon steel shell and a thick Red (RAL 3011) epoxy powder exterior provides excellent protection against moisture and oxidation, making it durable enough for various mechanical room environments.
Customized Colors & Packaging
We offer a wide range of customization options to match your exact needs - from custom colors to branded packaging and logo design.
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Downloads & Certification Links