The 7 Best Flow Switches

Editor's Notes

February 10, 2021:

It was a relatively painless round of updates, as all of the hardware we selected last time around continued to sensible selections for the category. We did, however, wind up making one new inclusion: The W.E. Anderson FS-2, which caught our eye with its adjustable paddle that can accommodate one- to eight-inch pipes, effectively making it a one-size-fits-most option. That, in combination with its IP64 dust and water resistance and 10-amp current rating – which is enough to fire up some light-duty equipment without mucking about with relays – sent that option right to the top of our list.

August 28, 2019:

Flow switches, which are sometimes referred to as flow indicators or sensors, integrate electrical circuitry into plumbing systems, reacting to the flow of liquids or gases in pipes, and activating associated equipment.

There’s a long list of possible applications for these devices, but some common cases include hot tubs, boilers and pumps. Which flow switch is perfect for you is going to depend largely upon your intended use for the part. Here’s a few things to remember to consider:

Device sensitivity: generally expressed in gallons-per-minute (GPM), this rating determines the amount of pressure required to push the switch to its energized state. Switches are available with both fixed and adjustable sensitivities.

What size of pipe are you monitoring? In-line flow switches will be compatible with only one size of pipe, so make sure you get it right! External paddle switches, which typically attach to the system via a reduction tee, are a little more forgiving in this respect, and can typically accommodate a range of pipe sizes. Some options, such as the McDonnell & Miller FS4-3, will include several sizes of paddle.

Tip: External switches can also help save you a lot of time down the road when it comes time to replace the switch!

How much power are you trying to switch? If you’re looking to control a relatively small load, for simplicity’s sake you can probably get away with installing a line-voltage option that wires straight up to your equipment. But if you’re looking to push a bit more power, you might need to consider using a control-voltage switch that wires up to a magnetic contactor, and control your equipment through there.

If you’re monitoring the flow of salt water or chemicals, make sure that all the wetted parts of your new purchase are rated to do so. We strongly recommend consulting a reputable, licensed electrician before attempting to install your new flow switch.