What is the Jet Pump on a Jet Ski? [Jet Ski Pump Explained]
The pump is the propulsion system of the jet ski. It produces a water jet that propels and steers the machine. The key components of this pump are the impeller and the wear ring, which are nestled in a metal pump housing. On the rear end of the pump, you can find the jet nozzle, which speeds up the water even more and controls the direction of the waterjet.
If you want to learn more about this important device, you’ve come to the right place.
We at JetDrift have compiled all you need to know under one roof!
What is the Jet Pump on a Jet Ski?
The jet pump on a jet ski is a device designed to generate the water jet for propulsion. Each jet ski utilizes a high-performance axial-flow jet pump that provides plenty of thrust to propel the machine.
As the name suggests, a jet ski pump is a type of centrifugal pump that houses an impeller and vanes to axially direct the water flow.
Where is the Jet Pump on a Jet Ski?
The pump on jet skis is located at the stern of the hull, below the waterline. Viewed from the outside, the pump is invisible since it’s nestled in a nook on the bottom of the hull and covered by the ride plate.
Behind this grate, there’s a large metal plate, which is referred to as the ride plate. Removing this plate allows access to the entire pump assembly.
The pump is also accessible and removable from the back of the ski. However, when doing it this way the reverse bucket and the jet nozzle have to be removed upfront.
What are the Components of a Jet Ski Pump?
The jet ski pump features many different components, all of which are enclosed in a sturdy pump housing.
Without further ado, the components of a jet ski pump are as follows:
- Pump housing
- Wear ring (on certain models)
- Impeller cover (a.k.a. pump nose cone)
- Impeller shaft
- Jet pump bearing
- Circlips, double lip seals, O-rings, spacers, screws
- Venturi nozzle (a.k.a. jet or steering nozzle)
Let’s drill into the details and talk about the specifics of each of these units!
Jet Ski Pump Housing
The pump housing is the metal base of the jet pump. This cylindrical metal unit features vanes and a stator accommodating the impeller shaft and bearing. The pump housing also encloses the wear ring and the impeller, which is attached to the engine by a direct driveshaft.
Surprisingly, the pump housing on early jet skis was made of plastic. These units gained a bad reputation for poor durability and reliability.
Because of this, in the ’90s, aluminum pump housings became more prevalent in jet skis. Certain models like 2-stroke Sea-Doos were manufactured with composite pumps, which featured bronze vanes that were installed in a plastic or aluminum housing.
The pump housing of modern jet skis is cast aluminum or high-quality stainless steel for optimum durability.
The shell of the pump housing encloses a set of vanes (a.k.a. stator vanes), which are small metal plates mounted in a radial direction. These vanes are intended to straighten out the water flow and increase the velocity.
In other words, due to the impeller’s rotating motion, water starts to swirl inside the pump. This is where the stator vanes come into play.
Mounted directly behind the impeller, these little fins effectively decrease the rotational motion of the water, so that more energy can be used for the thrust.
How many vanes does a jet ski pump have?
As a rule of thumb, the pump of vintage 2-stroke jet skis featured 5-6 vanes, while modern skis typically have 6-10.
High-performance aftermarket pumps are often designed with 10-14 vanes for higher efficiency. The more vanes a jet ski pump has, the more efficiently it can smooth the turbulent water flow. On the other hand, they put greater strain on the engine.
In the center of the pump housing, there’s a stator held in place by the vanes. This stator includes the impeller shaft and a bearing sealed by O-rings and rubber seals.
The wear ring is an impeller liner that ensures the critical spacing between the impeller blades and the pump housing. It’s typically plastic or stainless steel and pressed into the pump housing.
A tight clearance between the impeller and the wear ring provides higher pump pressure and prevents cavitation issues.
As the name suggests, this ring is a wear item that must be replaced in case of damage or excessive wear.
Not every jet ski features a wear ring. On certain models, the pump wall acts as a wear ring. The drawback of this design is that the entire pump housing has to be replaced in case of damage.
Impeller and its Features
Another key feature of a jet ski pump is the impeller, which is a kind of propeller. But unlike the exposed dangerous propellers of boats, the impeller on a jet ski is completely enclosed.
This configuration ensures safe operation, as the spinning impeller is out of reach.
Another advantage of this design is that it allows the jet ski to run in shallow water. (However, jet skis require at least a 3-foot water depth to run safely.)
Vintage jet skis featured aluminum impellers, while the modern machines come with stainless steel impellers.
Jet ski impellers typically feature 3 or 4 blades depending on the make and model. The geometry of the impeller is no less important, which is often characterized by the pitch.
Some are designed for the highest top speed, while others are for the best acceleration. In most cases, stock PWC impellers are tuned for a great overall performance.
The impeller is mounted on a stainless steel shaft, known as the impeller shaft. The end of this shaft is pressed into the pump bearing, which sits behind the impeller.
The pump bearing is a special conical bearing pressed into the stator section of the pump. It’s sealed with double lip seals, O-rings and held in place with circlips.
The impeller is mounted on the impeller shaft while its front is attached to the engine via the driveshaft.
On the rear end of the stator, you can find a bullet-shaped plastic unit labeled as impeller cover (a.k.a. pump nose cone). The name of this device is quite misleading since it doesn’t cover the impeller but instead, the rear end of the pump bearing.
It’s fastened to the pump housing with screws and faces towards the jet nozzle. Besides sealing, another important role of this pump nose cone is to prevent rattles and cavitation in the pump.
The most advanced models can preload the pump bearing, reducing wear and the chances of failure.
Also known as the steering nozzle, the venture nozzle is designed to speed up the water jet and control its direction.
It’s mounted on the rear end of the pump and attached to the handlebars via steering cables. Moving the handlebars turns the jet nozzle, which steers the jet ski.
How Does a Jet Ski Pump Work?
A jet ski pump works the same way as any ordinary jet pump; it uses an impeller and a nozzle to speed up the water. It sucks water through the intake grate, speeds it up, and squirts out the stern through the steering nozzle. This water jet propels and steers the jet ski.
To be more precise, the jet ski pump operates on the principle of the Venturi effect and a high-pressure fluid jet.
Therefore, it’s safe to say that this pump is virtually two pumps in one unit: a jet assembly and a centrifugal water pump driven by an impeller.
Jet skis come with a direct drive system, meaning that the engine directly drives the impeller. When you fire up the engine, it immediately starts spinning the driveshaft.
This driveshaft passes through the hull and connects to the impeller. There are no gears, no awkward drivetrain like on snowmobiles and ATVs, just a simple shaft that directly transfers power from the engine to the pump.
The spinning impeller generates negative pressure on the pump’s inlet side.
Since the entire pump assembly sits in the water, the impeller starts to suck water through the water intake. Water passes through the impeller, which forces it towards the jet nozzle.
In this way, the pump translates the rotational motion generated by the engine into usable power.
However, water does not simply squirt out of the rear end of the pump as it goes through the jet nozzle. This device is a conical metal nozzle mounted on the rear end of the pump.
The jet nozzle uses the Venturi effect to increase the speed of the waterjet. The Venturi effect states that if fluid passes through a pipe with a constriction in it (here the jet nozzle), it must speed up in the restrictive area. Also, its pressure drops and generates a vacuum.
In other words, the jet nozzle increases the speed of the water due to its design. Think of this device as a nozzle sprayer on a garden hose. It makes the water flow faster while reducing the line’s diameter.
If you want to accelerate the jet ski, you must depress the throttle lever. This causes the impeller to spin faster, increasing the speed of the water flow.
The faster the water squirts out of the pump, the faster the jet ski moves forward.
Releasing the throttle to idle causes the impeller to spin much slower. However, it’s always spinning when the engine is on since it lacks gears.
Because of this, older jet skis start slowly moving as soon as you fire up the engine. The latest models come with a brake and reverse system that features a foldable reverse gate to solve this issue.
This gate is intended to reverse the flow of water coming from the pump, which can be used for either decelerating or reversing the machine.
When you start the engine, this gate is partially lowered to return only a small portion of the thrust. This way, the pump can balance forward and reverse thrusts to hold the jet ski in place.
This innovative solution gives you the feeling that the machine has a neutral gear.
The jet nozzle is also used to steer the jet ski since it’s linked to the handlebars via steering cables. Turning the handlebar moves the nozzle from side-to-side, which redirects the water jet.
Takeaways: FAQs About the Jet Ski Pump
As a takeaway, we’ve answered the most common questions about this key device!
What Propels a Jet Ski?
As the name suggests, a jet ski is propelled by a jet propulsion system. The pump on a jet ski is a centrifugal water pump completed by a jet nozzle. This device accelerates the water, forcing it through the nozzle at a very high speed. This squirting water jet propels and steers the jet ski.
Which Component of a Jet Ski Pump Accelerates the Water?
The water in the jet ski pump is accelerated by the impeller. This device is very similar to the propeller of boats, but it sits in an enclosed pipe. You can read more about jet ski impellers in this detailed post.
Where is the Intake Located on a Jet Ski?
The water intake on a jet ski is positioned directly in front of the jet pump and covered by the intake grate.
How Does Water Flow Through a Jet Ski?
Water enters the jet ski through the water intake and flows into the pump. Inside the pump housing, the impeller accelerates the water and forces it through the stator vanes. Then the water passes through the pump nose cone and finally squirts out of the jet nozzle on the stern of the ski.
What is the Purpose of the Stator Vanes in a Jet Ski Pump?
The stator vanes in a jet ski pump are small metal fins mounted inside the pump housing. They are intended to straighten the swirling motion of the water and increase its velocity. In this way, more energy given to the water can be used for thrust.
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