Repairs & how-to
How to re-pressurise a pressure tank
A pressure tank has an air cushion (behind a bladder) that stores pressure so your pump isn’t starting every time you crack a tap. When that air leaks away over time the tank goes waterlogged, and the pump short-cycles, rapid on-off that wears it out. Recharging the air often brings it straight back.
How a pressure tank works
Inside is water on one side and compressed air on the other, split by a bladder. The air is pre-charged to a set pressure. As you use water the air pushes it out; when the pump runs, it re-fills. Over years the air slowly escapes, the water side takes over the whole tank (waterlogged), and the cushion is gone.
Signs it needs recharging
- The pump cycles on and off rapidly in short bursts.
- Tapping the tank sounds solid all the way up (a healthy tank sounds hollow on top, solid at the bottom).
- Water spits at the tap.
- The pump runs far more often than it used to.
How to check and recharge
- Switch off the pump and open a tap to drain the tank’s water pressure to zero.
- Find the air valve on top of the tank (like a car tyre valve).
- Check the pressure with a tyre gauge. The correct pre-charge is usually a couple of psi (about 15 kPa) below the pump’s cut-in pressure, check your pump’s spec.
- If it’s low, add air with a pump or compressor to the correct pre-charge. If you hear or see water come out of the air valve, the bladder has failed and the tank needs replacing.
- Refit the valve cap, restore power, and check the cycling has settled.
When it’s beyond recharging
If the bladder is split (water comes out of the air valve, or it won’t hold air at all), recharging won’t help, the tank needs replacing. That’s a straightforward swap.
Safety: Drain the tank’s water pressure before checking the air charge, and don’t over-inflate. Isolate the pump’s power while you work.
Common questions
What pressure should I set it to?
Usually about 2 psi (15 kPa) below the pump’s cut-in (turn-on) pressure. Your pump’s manual lists its cut-in; set the tank’s air pre-charge just under it, with the water side drained.
How often do tanks need recharging?
Check it if the pump starts short-cycling, otherwise every year or two. A tank that won’t hold its charge at all has a failed bladder and needs replacing.