Updated February 13, 2021 by Will Rhoda

The 7 Best Flow Switches

video play icon

This wiki has been updated 8 times since it was first published in August of 2019. Flow switches, which are sometimes referred to as indicators or sensors, integrate electrical circuitry with plumbing systems, monitoring the movement of gases or liquids inside pipes and controlling associated equipment. Prior to making a purchase in this category, consult a licensed electrician to arrange for installation and verify that the unit meets all necessary specifications. When users buy our independently chosen editorial picks, we may earn commissions to help fund the Wiki. If you'd like to contribute your own research to the Wiki, please get started by reviewing this introductory video.

1. W.E. Anderson FS-2

2. Gems Sensors FS-380

3. McDonnell & Miller FS4-3

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.

4. Dwyer Flotect Series V10

5. Gems Sensors FS-500

6. General Pump 100975

7. Aqualarm Liquid Detector


Will Rhoda
Last updated on February 13, 2021 by Will Rhoda

After deciding that the pen was mightier than the pliers, Canadian electrical contractor William Rhoda abandoned his career and headed back to college, where he majored in marketing and advertising and won a scholarship along the way to earning a diploma in creative communications. His past career landed him a depth of knowledge in tools and hardware, while his current career schooled him in audio, video and camera equipment. During his leisure time, he’s learned lots about outdoor gear, and years of tiresome backyard maintenance have taught him all about pools and hot tubs. His recreational pursuits include rest, relaxation and revolutionary action, and his roommate’s a hairless cat.


Thanks for reading the fine print. About the Wiki: We don't accept sponsorships, free goods, samples, promotional products, or other benefits from any of the product brands featured on this page, except in cases where those brands are manufactured by the retailer to which we are linking. For more information on our rankings, please read about us, linked below. The Wiki is a participant in associate programs from Amazon, Walmart, Ebay, Target, and others, and may earn advertising fees when you use our links to these websites. These fees will not increase your purchase price, which will be the same as any direct visitor to the merchant’s website. If you believe that your product should be included in this review, you may contact us, but we cannot guarantee a response, even if you send us flowers.