Pumping from a tank to a tap: a simple pressure setup

A tap that works at the flick of a wrist is a small system doing several jobs in order. Break it into four parts and it stops being mysterious: a tank, a pump, a pressure switch and the tap.

What each part does

The tank holds the water. Keep it at or above the pump if you can, because many centrifugal pumps are placed below the level of the water they draw from¹.

The pump moves water from the tank into the pipe to the tap.

The pressure switch is the clever bit. A pressure switch operates an electrical contact once a set pressure is reached, and it can be made to act when pressure rises or when it falls². For a water pump, that means the switch can start the pump when pressure drops as you open a tap. A listed use is to switch a household well water pump automatically when water is drawn from the pressure tank².

The tap is the outlet. Opening it lets water out, and the pressure in the pipe falls. That fall is the signal.

The sequence

Walk through it once and the logic is plain. Pipe pressure sits at the switch's upper setting while the tap is shut. Open the tap and pressure drops. The switch sees the fall, closes its contacts and the pump starts. Shut the tap and pressure climbs back up. The switch opens and the pump stops.

The switch's settings can often be changed. Wikipedia says a pressure switch may be adjustable by moving the contacts or adjusting spring tension². Use your maker's manual for how to adjust it on your model. Don't guess, because a wrong setting can leave the pump running or never starting.

A small cabin, shed or camper

A university extension guide notes that a solar pumping system can meet the indoor plumbing needs of a small building or a remote cabin³. That's close to the job you're setting up, just on a smaller scale.

Two small parts that save trouble

A check valve. It lets water through one way only. One guide says a check valve should be fitted if the pump doesn't have one built in, to stop water flowing back³. That guide is about a well, but the idea carries over to any pump below a line of water.

An accumulator. This is a small pressurised vessel. It can hold pressure through slight leaks without the pump switching on and off constantly⁴. The page says it's placed close to the pump, with a non-return valve preventing flow back to the pump⁴. If your pump switches on and off too often, an accumulator is the next thing to read about.

What mistakes look like

• Pump won't start when you open the tap. Check the power first, then the switch.
• Pump starts but delivers no water. Check that the suction side is airtight and the strainer is clear. A pump maker's checklist lists both⁵. The steps in what to do when a pump loses its prime cover the rest.
• Pump runs and runs. Look for a dripping tap or fitting, since a leak keeps pressure from building. Then check the manual for the switch settings.

Wiring and safety

Wire the pump, switch and battery as the maker's manual says. Isolate the battery first, before any battery lead, fuse or cable is connected or disconnected. A pump maker's checklist also opens with locking out power⁵. If you're not sure, ask a licensed electrician. This isn't routine DIY.

Any job at mains voltage is different. Fixed 230V wiring, switchboards and grid connection are licensed electrical work in Australia. New South Wales requires an electrical licence for any electrical wiring work, whatever the cost or type⁶. In Western Australia, an unlicensed person can't legally carry out electrical work, including changes to fixed wiring⁷. Other states have their own rules, so ask your state regulator.

If the tank sits higher than the tap, you might not need a pump at all. Choosing between gravity and a pump helps you decide.