How Do Bathtub jets Work?

"Jet" - you likely see this word all this time but never think about what it actually means. A “jet,” by definition, is any apparatus that creates an intense stream of gas or liquid by forcing it out of a smaller opening than its intake. So, in essence, showerheads, jet aircraft engines, sprayer hoses, and Bathtub jets all operate under the same physical laws. Pretty cool, right? Of course, these all vary in degrees of intensity — you don't want your hot tub to fly, after all — but, the concept is still the same. Now that we’ve cleared that up, let’s get down to the nifty ways in which your Bathtub jets create those massaging, relaxing, and bubbling streams.

Bathtub jets work via two inlets that feed each jet of your hot tub, one for water and one for air. The nozzle is the portion of the jet where the water-air mixture reaches the bathers in the actual tub. (Some Bathtub jets have double-headed nozzles, but the concept is the same.)

How Bathtub jets Work... Thanks to an 18th Century Italian Physicist

While your hot tub uses an air blower to create those bubbles we all love so much, the jet assembly itself also draws in its own air supply by way of a pretty cool anomaly of physics known as the “Venturi effect.” When Giovanni Battista Venturi discovered this effect in the 1700s, he probably had little thought to revolutionizing everything from clarinets and faucets to scuba diving regulators and — you guessed it — hot tubs. Using the awesome wizardry — oops, we mean science — of the Venturi effect, the aspirator draws air into jets' water supply using negative pressure created by a fast-moving stream of water.

Because of the awesome technology found in your hot tub you are likely wondering if a hot tub can actually be used as a time machine, and the answer is “yes,” but only into the future, and only in real time. All jokes aside, there is some really amazing technology at play that allows your Bathtub jets to function as reliably as they do.

The Awesome Science of Bathtub jets

If you remove one of your hot tub’s jets and take a look inside you will see something that can be found in all Bathtub jets — a gradual tapering toward the nozzle. As water and air move through the lines of the jet, this mixture ends at its tapered nozzle. This is where the real Venturi effect magic takes place. As the water-air mix reaches this point, something incredible happens. Since the nozzle tip is smaller than the pipe delivering the water and air, the speed (or velocity) of this mixture actually increases, yet becomes less compressed (or pressurized). Since the water and air exiting your Bathtub jets is at a lower pressure than the atmospheric pressure around your hot tub, air is forced into the plumbing through the air control, creating that massaging jet action we all enjoy so much.

What Causes Bathtub jets to Not Work?

Not to sound pessimistic, but every mechanical apparatus ever created will someday fail. Therefore, there will always be a need for replacement parts and hot tub repair techs. Bathtub jets can fail in a number of interesting and spectacular ways, such as water jetting out of the air controls (instead of through the jet nozzles), or the reverse — a jet that vacuums in water instead of pushing it out.

And while this may seem simple and a no-brainer, Bathtub jets can also stop moving because they are actually just turned off.  The flow of water can be controlled by twisting the jet collar on many jets, so be sure to make sure that's not the case before reading up on the below!

However, fortunately for all of us hot tub owners, when spa jets do actually fail it’s typically a pretty humdrum affair; more often than not, a failure is due to a clogged jet or filter, a failing pump, some other cause that reduces the flow of water. If your Bathtub jets are currently not working as they should, here are a few good ways to diagnose and fix the issue:

• Dirty filter — A dirty filter can limit the amount of water coming into the water inlet, reducing the pressure and flow that is necessary in bringing air into the mix. So, if it’s been a while since you last changed your hot tub filter, this would be a great (and cost-effective) place to start! Too much water coming into the inlet can also cause problems and is likely the result of a pump issue.
• Pump issues — Sometimes it’s not the jet itself that is failing, but the pump, so it’s always a good idea to do some troubleshooting so you don’t end up replacing the wrong part. When a hot tub has a pump issue, output from the jet nozzles will be noticeably reduced and you may hear a squealing or wheezing noise coming from the jets. Too large of a pump can also create backpressure between the inlet and ball of the nozzle. Sometimes, modifications to the nozzles can relieve this pressure, but going back to a smaller pump may also be in your best interest.
• O-ring and gasket failures — In most Bathtub jets made today, the high- and low-pressure areas are sealed off using either an O-ring or gasket. When these degrade or become dislodged you will notice either reduced jet performance or no pressure coming from the jets. (This is one of cause-effect scenarios we mentioned previously about water backing up and coming out of the air inlets.)