Checking the air pressure in my water pump.. What are you going on about?!

Yes, you read that right. Most water pumps will have a separate tank called the pressure tank that acts both as a reservoir and a shock absorber. By keeping water pressurised, the pressure tank acts like a buffer and allows for both instantaneous and almost consistent water pressure output before the pump starts up.

Why a pressure tank?

The pressure tank design itself has been around for a very long time and while it is a tried and true design - it does have its downside, but the pros far outweigh the cons.

As the air inside the pressure tank is compressible, the pressure tank absorbs the shock of "water hammering" effect when you turn on and off your tap. This in turn will save your pipes from undue stress and leaks - especially useful for houses with older pipes.

In this example, we'll be using Welflo pumps for demonstration purposes but the steps should work the same for all water pumps equipped with a pressure tank. Just be sure to check your user's manual for the exact pressure settings.

While Welflo booster pump models that are equipped with pressure tanks are slightly more expensive the benefits you get is three folds - longer pump life (from not having to work more often especially for short duration of water usage), consistent pressure and trouble-free (read: leak-free) plumbings.

So what's the downside with a pressure tank-equipped pump? 

Like your tyres, the pressure inside the pressure tank will also slowly leak out, when that happens, water would trickle out from the taps when you open and flow out in an inconsistent manner or pulsates.

You may also notice that your pump will take a longer time before it starts pumping (also known as "cut-in") and a longer time to stop (also known as "cut-out") - apart from the frustration of having to wait for your pump to build up pressure, this also causes extra workload on your pump which will translate to more wear and higher electrical bills.

Before you call in the plumber or pump technician, the answer to your water pump woes might just be a few simple steps away..


Things you'll need to balance your pressure tank.

Depending on pump model, you'll need:

a.) a No.2 Philips screwdriver (Welflo WFSM405AX only).
b.) a floor or hand pump - a small emergency tyre inflator pump for your car will also work.
c.) an ACCURATE pressure gauge - it can be either analog or digital but has to be fairly accurate!


1. Turn off the power to the mains and wait 5 minutes before working on the pump. While waiting, turn on a tap to de-pressurise the pressure tank - you might want to leave it trickling.

If your pump comes with an external housing (like the WFSM405AX), start by removing the plastic housing by loosening the two Philips bolts on either side of the pump next to the inlet and outlet ports.

WFSM405AX only: As the housing is held down via friction from the bolts, you do not have to completely remove the bolts - loosening the bolts is enough to allow you to slide the housing up.


2. Locate the pressure tank and remove the valve cap - on the Welflo WFSM405AX, it's a blue plastic cover which you can unscrew counter-clockwise with your fingers. On the Welflo WFSM60A, the pressure tank uses a metal valve cap and unscrews in the same counter-clockwise manner.

3. Check the pressure inside the pressure tank with a pressure gauge. If the pressure is below 20psi (1.4 bar), attach the pump and inflate it to anywhere between 23psi (1.6 bar) to 29psi (2.0 bar). You can release excess air by momentarily depressing the valve core.

We settled for 27psi (1.8 bar) as its roughly in the middle of the two ranges and should compensate for any error in temperature fluctuation or from the pressure gauge.

4. Replace the valve cap (and housing cover) and turn your Welflo pump back on.

Precautionary notes: 

If an electric air pump is used, just be mindful of how fast it inflates the pressure tank - it should take less than a few seconds to fully inflate the pressure tank. In this example, it takes just two to three strokes with a mountain bike hand pump to get the pressure tank in the WFSM405AX from 19psi (1.3 bar) to 29psi (2.0 bar).

Additionally, as almost all water pumps uses a conventional Schrader valve, like those on your car, motorcycle and some bicycles, inflating or 'balancing' the pressure tank is essentially the same as inflating your tyres - the only difference is the volume of air.

Job done!

What you're actually inflating isn't the pressure tank itself but an isolated chamber of air inside the pressure tank separated by a diaphragm. The diaphragm separates the inlet water from the air and determines the overall pressure within the tank.

For Welflo pumps, the cut-in and cut-off pressure has been pre-set from the factory via the Pressure Adjustment Switch to work in a typical domestic environment based on the range of pressure from 23psi (1.6 bar) to 29psi (2.0 bar) and needs no further adjustments.

All you need to do now is to keep an eye on the pressure every now and then and enjoy having your pump back in action again!