Pressure Vessels

A pressure vessel stores water under pressure in your system. When you open a tap, small draws come from the vessel instead of the pump, so the pump starts less often and runs for longer when it does. That means steadier pressure and a longer pump life. In our drinking-water vessels, the water sits inside a potable-grade membrane and never touches the steel.

It depends on the job:

Tell us the pump and the pressure you need, and we'll size the vessel and set it up. See all pressure vessels.

A pressure vessel stores water under pressure so the pump starts less often. An expansion vessel sits on a closed heating circuit and takes up the extra volume as the water heats, so the pressure stays in range and the relief valve stays shut. Don't swap one for the other. Our MaxiVarem LR heating expansion vessels are for closed heating circuits only, not drinking water. For drinking water, use a potable vessel such as the Varem ExtraVarem, where the water sits inside a potable-grade membrane and never touches the steel.

Fit it close to the pump outlet, ideally on a brass 5-way connector, which joins the pump, vessel, pressure switch, gauge and outlet in one fitting. Add an isolating valve so the vessel can be serviced without draining the system. Our horizontal vessels (36–100L) have a pump stand built in, so the pump sits on top of the vessel.

A pressure vessel needs the right air pressure (pre-charge) to work. Check it once a year:

1. Switch off the pump at the electrics.
2. Open a tap until the water stops flowing and the water side has no pressure.
3. Check the air valve on the vessel with a tyre pressure gauge.
4. Compare the reading with the correct setting:
   • Fixed-speed pumps: 0.2 bar below the pump's cut-in pressure.
   • Extra vessel added to a Walrus HQ_B: match the air charge in the pump's built-in vessel, about 1 bar.
   • Variable speed pumps: 20% below the running pressure.
   • PowerBox: 1.5–1.8 bar.
5. Top up with a tyre pump if it's low.

If water comes out of the air valve, the membrane has failed and the vessel needs a new membrane or replacing.

It depends on the pump:

• Walrus HQ_B: has a pressure tank built in, so most installations don't need a separate vessel. Where there are a lot of draw-offs or outlets, like a hair salon or a building with many wash hand basins, installers sometimes add one. If you do, match its air charge to the pump's own vessel, about 1 bar.
• EBARA Hydrostation: comes with a 3L pressure vessel to prevent frequent cycling.
• PowerBox: the Economy has its vessel in the controller. The Standard has one fitted externally. For the Variable, the vessel is supplied separately.

For other systems, a pressure vessel reduces how often the pump starts and extends its life. We'll tell you whether your setup needs one.

In almost every case, yes. Without one, the pump would start every time someone opened a tap, even for a glass of water. Our Stairs motors are rated for a maximum of 40 starts an hour, so constant starting shortens their life. A correctly sized vessel gives you steady pressure and fewer, longer pump runs. Our borehole pressure system comes with a 60L vessel as standard, horizontal or vertical, and we supply drinking-water vessels from 2L to 1000L.