Water flowing through onboard pipes undergoes pressure spikes every time a faucet is closed. An expansion tank acts as a hydraulic buffer: it absorbs these peaks, protects the joints, and prevents the freshwater pressure pump from cycling on needlessly every time a glass of water is drawn. If you feel vibrations or notice a stuttering flow, the system is probably working outside its range due to the lack of a steady pressure reserve.
Choosing the right tank is not just a matter of space in the bilge. Capacity in liters must be proportional to the output of your freshwater pressure pump. A tank that is too small remains ineffective, while an oversized one wastes useful volume. When we assist you with pre-sales advice, our goal is to make sure the part you choose matches your system's characteristics: maximum supported pressure, fitting diameters, and type of internal membrane.
Our standard approach prioritizes full transparency on delivery times. We know that a plumbing failure means being without water, a situation that needs to be resolved quickly. That is why every item in our Osculati catalog comes with clear information on availability and shipping. If you have doubts about a fitting's compatibility or the ideal mounting position, contact us before finalizing the order: a pre-order technical check avoids unnecessary returns and wasted time.
How to size and install the tank correctly
Installation should be as close as possible to the freshwater pressure pump outlet, preferably in a vertical position to allow the internal membrane to work correctly and ensure an adequate air reserve. Keep in mind that the tank's pre-charge pressure must be slightly lower than the pump's cut-in pressure, typically about 0.2-0.5 bar less, to allow the system to accumulate water efficiently.
- Always verify that the tank's maximum pressure rating exceeds the freshwater pressure pump's operating pressure.
- Make sure you have enough room for mounting, accounting for the bend radius of the inlet and outlet hoses.
- Check fitting compatibility, avoiding multiple adapters that create restrictions or potential leak points.
- If you use seawater, confirm that the materials are compatible and resistant to galvanic corrosion.
- Periodically inspect the internal membrane and the inflation valve to prevent air loss that would render the tank useless.
What exactly is an expansion tank for?
It maintains constant pressure in the hydraulic system, preventing the freshwater pressure pump from cycling on every time you open a faucet. This reduces mechanical wear on the pump and annoying vibrations in the pipes.
How do I choose the capacity in liters?
Capacity depends on your pump's output. For a standard recreational pump, a 0.5 or 1-liter tank is usually sufficient. Larger vessels with higher flow demands require tanks with greater volume to stabilize the system.
Can an expansion tank be repaired?
Most commercially available tanks use sealed membranes. If the membrane punctures or loses its seal, the entire component usually needs to be replaced to ensure the safety of the hydraulic circuit.
Where should it be mounted in the system?
The ideal location is downstream of the freshwater pressure pump, on the delivery circuit. Proximity to the pump is essential for effectively dampening water hammer before it reaches the boat's pipes.
Why does the pump keep cycling on its own?
If the pump cycles without any faucet open, you may have a leak in the system, a check valve that is not sealing, or the expansion tank has lost its air charge and can no longer maintain pressure.
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