Pump Pressure

[Dorny119]

I am curious if anyone has done any tests to see how much pressure is generated at the cooling line inlet. For example, if we took a cooling line end, capped it off, and put a gauge right there, what would the gauge read? Just out of curiosity. Thanks!

 

[Myself]

It's very low......like 15psi.

 

[503701]

Curious about GPM numbers now

 

[JC-SuperJet]

Had done the Calcs before on previous Thread - she gone. Almost all my Posts (1000+) got deleted accidentally ...

So Pete and Repete...

Example: Kawasaki 750 SX: Stock Thrust = 550 lbs and Pump Diameter = 140 mm (the Kaw 750 SX is similar to Pump Size and Engine Power as SJ)

Pressure = Force/Area

Pump Diameter in Inches= 140mm/25.4mm = 5.5 in. so Pump Area = pi x (diam x diam)/4 = 3.14 x (5.5" x 5.5")/4 = 24 sq. in.

Pressure = 550 lb/24 sq. in. = 23 psi max peak pressure. Cooling Water Tap is at the Pump, so the Cooling Water should have about the same Pressure.

 

[JC-SuperJet]

For GPM, let's grab the Kalkalata again. to do a very rough ballpark guesstimation...

Due to direct drive, when the Engine rotates 6000 rpm, the Pump also rotates 6000 rpm (it better! ). So need to find amount of Water processed in ONE Revolution and multiply that by rpms to find gpms.

Also need Pump Volume in Gallons. So, a SJ Pump measures 144mm Diameter and is about 3 inches long. Same as Volume of Cylinder so:

Pump Dia. = 144mm = 5.7 inches. Pump Area = 3.14 x (5.7 x 5.7)/4 = 25 sq. in.

Pump Volume = Base x Height = 25 sq. in. x 3 in. = 75 cubic inches. *This is maximum amount of Water that can fit in the Pump without an Impeller*

Converting to gallons,, since 1 cubic inch = 0.004 gal, then 75 cubik inches x .004 = 0.3 gallons is the most that can fit in the Pump Space w/o an Impeller.

So for every complete revolution, 0.3 gallons of Water max can flow thru the Pump. In a sense, the Impeller acts as a Throttle Valve, "fully opening" each revolution.

But the Impeller has 3 Blades or "Paddles", so the Pump is actually moving/sweeping 3 times the Pump Space Volume.

So each Minute, 3 x 0.3 gallons flows thru the Pump. Then actual flow rate is about 0.9 gpm.

At 6000 rpms, 0.9 gal/rpm x 6000 rpm = 5400 gallons max processed per minute = 90 gal per second

To check, let's see how much Thrust is produced by 90 gal per second.

Gallon of Water weighs about 8 lbs, so 90 gallons weighs 720 lbs or Thrust is about 720 lbs per second.

This is ballpark to the 550 lb Kaw 750 SX Thrust rating spec'd by Kawasaki.

Also, since Jetski Pumps are not loaded perfectly and the Intake water is aerated aka "dirty" or foamy, the use of a one-second time window to calculate Thrust is not far from the real instantaneous Thrust number, which would be somewhat lower.

Any Pump Experts that can chime in and correct, support, confirm, deny, supplement or clean-up my getter'dun Calcs and Assumptions?

Every day is a School Day for me, so please comment and edumacate me...

 

[Harbor]

^^ your on one today, I like it

 

[JC-SuperJet]

A very simple way to figure the Water Pressure at the Pump Exit Nozzle is to guesstimate the height in feet of the Jetski Pump "Fountain" and divide by 2.3 ft/psi.

Xample: Fountain is about 23 ft high, then Exit Nozzle Pressure 'tis about 23ft/2.3ft/psi = 10 psi

If the Fountain is about 30 ft high then: 30/2.3 = 13 psi

 

[WFO Speedracer]

When I was trying to figure this out on a Seadoo trim setup I didn't want to do all the calculous so I asked WETWOLF since his pump cones were pressure operated I thought he would know, he gave me a pressure of 35 PSI which I used to order the trim cylinders I made the POPS trim setups with, that worked out really well so he had to be pretty close.

 

[Dorny119]

Holy crap this is awesome. Thanks all! (mostly JC lol). I asked because i have been experimenting with a on/off valves to temporarily dry my B-Pipe for top speed runs. My pipe is currently tuned for mid-Range, and i ran 49mph GPS. I may even put more water in for lower RPM power band, which would probably take my top speed down to 47-48mph (this was my top speed last time i was tuned for low RPM.

I installed a toggle on-off valve where my choke cable used to be, and when flipped off, my top speed is 52mph! Obviously i have dual cooling with a dedicated exhaust line. My valve cuts off that exhaust line. So, for about 15 seconds, i kill water to my pipe. I have not yet melted a coupler. I am not trying to find out how long i can run dry for lol.

I asked the question because I wanted to make sure that if i hooked up a 12v solenoid valve with a momentary button mounted on the bars, that the solenoid could handle the pressure. Looks like good news! Even 35psi is not bad!!

 

[MTRHEAD]

I did some testing on a sxr800 superstock in 03 and I recall the max pressure in a cooling line of around 40psi We used to run 2 - 1/2 lines in and 3 out head. Can’t my find notes to double check.

 

[mikidymac]

For GPM, let's grab the Kalkalata again. to do a very rough ballpark guesstimation...

Due to direct drive, when the Engine rotates 6000 rpm, the Pump also rotates 6000 rpm (it better! ). So need to find amount of Water processed in ONE Revolution and multiply that by rpms to find gpms.

Also need Pump Volume in Gallons. So, a SJ Pump measures 144mm Diameter and is about 3 inches long. Same as Volume of Cylinder so:

Pump Dia. = 144mm = 5.7 inches. Pump Area = 3.14 x (5.7 x 5.7)/4 = 25 sq. in.

Pump Volume = Base x Height = 25 sq. in. x 3 in. = 75 cubic inches. *This is maximum amount of Water that can fit in the Pump without an Impeller*

Converting to gallons,, since 1 cubic inch = 0.004 gal, then 75 cubik inches x .004 = 0.3 gallons is the most that can fit in the Pump Space w/o an Impeller.

So for every complete revolution, 0.3 gallons of Water max can flow thru the Pump. In a sense, the Impeller acts as a Throttle Valve, "fully opening" each revolution.

But the Impeller has 3 Blades or "Paddles", so the Pump is actually moving/sweeping 3 times the Pump Space Volume.

So each Minute, 3 x 0.3 gallons flows thru the Pump. Then actual flow rate is about 0.9 gpm.

At 6000 rpms, 0.9 gal/rpm x 6000 rpm = 5400 gallons max processed per minute = 90 gal per second

To check, let's see how much Thrust is produced by 90 gal per second.

Gallon of Water weighs about 8 lbs, so 90 gallons weighs 720 lbs or Thrust is about 720 lbs per second.

This is ballpark to the 550 lb Kaw 750 SX Thrust rating spec'd by Kawasaki.

Also, since Jetski Pumps are not loaded perfectly and the Intake water is aerated aka "dirty" or foamy, the use of a one-second time window to calculate Thrust is not far from the real instantaneous Thrust number, which would be somewhat lower.

Any Pump Experts that can chime in and correct, support, confirm, deny, supplement or clean-up my getter'dun Calcs and Assumptions?

Every day is a School Day for me, so please comment and edumacate me...

That flow number seems really high.
I don't design pumps but I spec irrigation pumps all day and 5,400 gpm is really big.
In our industry 5,400 gpm @ 35 psi would take a big 13" diameter impeller with a 10" discharge centrifugal pump with a 150 HP engine.

 

[Storbeck]

Had done the Calcs before on previous Thread - she gone. Almost all my Posts (1000+) got deleted accidentally ...

So Pete and Repete...

Example: Kawasaki 750 SX: Stock Thrust = 550 lbs and Pump Diameter = 140 mm (the Kaw 750 SX is similar to Pump Size and Engine Power as SJ)

Pressure = Force/Area

Pump Diameter in Inches= 140mm/25.4mm = 5.5 in. so Pump Area = pi x (diam x diam)/4 = 3.14 x (5.5" x 5.5")/4 = 24 sq. in.

Pressure = 550 lb/24 sq. in. = 23 psi max peak pressure. Cooling Water Tap is at the Pump, so the Cooling Water should have about the same Pressure.

I like the application of fundamentals here, but I think there is an important thing you are missing, you are not factoring in the pressure at the *inlet* of the pump. At low speeds the pressure at the inlet of the pump will probably be below the static pressure, and at high speeds it is probably above static pressure.....I...think (?). That's a tough one for me to wrap my head around.

Also, very likely the thrust is not constant with speed, I have no idea if it would go up or down with higher speed (intuitively it seems like down, but I have a hard time wrapping my mind around this).

 

[Dorny119]

That flow number seems really high.
I don't design pumps but I spec irrigation pumps all day and 5,400 gpm is really big.
In our industry 5,400 gpm @ 35 psi would take a big 13" diameter impeller with a 10" discharge centrifugal pump with a 150 HP engine.

Besides that being a very quick Calc-stimate, I think the error is in multiplying by 3 (3 blades). I think one of each of those blades covers nearly one rotation right? So it's more like 5,400/3 in that case. That's 1800gpm.

EDIT: Although.. with 3 blades each moving the 3 inches of water for each rotation, then you WOULD mult by 3... so yea i think JC is really close.

 

[Dorny119]

I like the application of fundamentals here, but I think there is an important thing you are missing, you are not factoring in the pressure at the *inlet* of the pump. At low speeds the pressure at the inlet of the pump will probably be below the static pressure, and at high speeds it is probably above static pressure.....I...think (?). That's a tough one for me to wrap my head around.

Also, very likely the thrust is not constant with speed, I have no idea if it would go up or down with higher speed (intuitively it seems like down, but I have a hard time wrapping my mind around this).

What you are referring to is the acceleration of the water. Delta P is proportional to the acceleration. The pressure at the nozzle is the pressure at the nozzle regardless.

 

[JC-SuperJet]

Axial Flow (Jetski) pumps have large flow and low lift versus Centrifugal pumps have small flow and a high lift. Apples and Oranges.

If someone would use their Ski to Pump Water at WOT into a known volume Container and timed the fill-up time, actual GPM readings could be obtained.

No Jet Drive Pump OEM will release their Pump Curves and Specs; not Yamaha , Kawasaki, Seadoo, nor Berkeley nor Jacuzzi Bros. I searched and no joy.

 

[JC-SuperJet]

I like the application of fundamentals here, but I think there is an important thing you are missing, you are not factoring in the pressure at the *inlet* of the pump. At low speeds the pressure at the inlet of the pump will probably be below the static pressure, and at high speeds it is probably above static pressure.....I...think (?). That's a tough one for me to wrap my head around.

Also, very likely the thrust is not constant with speed, I have no idea if it would go up or down with higher speed (intuitively it seems like down, but I have a hard time wrapping my mind around this).

Yes, there is a performance contradiction for Jetski Thrust optimization. A few Balls in the Air to keep track of...

At low speed, we want a big Pump for slow incoming Water fed thru the Intake. But for high speeds, we want less Water/smaller Intake Duct and a smaller Exit Nozzle.

Both can be had according to Intellijet with variable Intakes and Exit Nozzles...

See attachment.

 

[kevbo]

Look up the dynamic pressure of water then figure the area of your nozzle. Measure your static thrust and you will find that any decent running ski will be over 70 PSI. Let me add that I have found it a lot easier to increase low speed thrust with a larger nozzle than it is by adding power. Our pumps like to flow more volume than they like making pressure.

 

[JC-SuperJet]

Okay, assuming there is no Current and only the Ski is moving:

Water (Fluid) Dynamic Pressure is based on Momentum Formula 1/2 Mass x V*2 or 1/2 x Density x Speed Squared

with Water Density in Slugs per Cubic Feet given rounded-up as 2 Slugs/cu. Ft. A Slug is a Unit of Force based on Gravity Acceleration. So 62.4/32.2 < 2 Slugs.

Let's pick 55 mph for the calc, but mph needs to be converted to feet per second, so 55 mi/hr x 5280 ft/3600 sec = 80.7 feet/sec

Then plug and chug with Slugs, Dyna-P = 1/2 x 2 Slugs/cu. Ft x (80.7 ft/sec x 80.7 ft/sec) = 6512 lbs/sq Foot = 45 lb/sq inch or 45 psi Dynamic Water Pressure

I'll venture that the Ski sinks about 6 inches in the Water, so the Water Static Pressure is equal to 6 inches of Water or half-a-foot of Water.

Thus Static Water Pressure = 0.5 ft x 1 psi/2.3ft = 0.21 psi Not worth including in a rough estimate.

So at 55 mph, the Ski Pump Inlet will see about 45 psi of incoming Dynamic Water Pressure.

So does that get added to the Pressure developed by the Jet Pump? Does it help or work against the Impeller? When does Pump Stuffing happen?

At what Speed does Water start to feel like Concrete?

At 70 psi, the Pump would throw a vertical Fountain about 160 feet high...

At 30 seconds of clip...

 

[WFO Speedracer]

I like turtles !

 

[kevbo]

Standups run on the surface so they never get clean water like a sitdown does. Standups need long shallow inlet ramps where sitdown inlets end up shorter after being optimized for their intended top speed. I built a load cell years ago and was able to get nearly 700 lbs of static thrust from 50mph Superjets with 85mm nozzles.