Kubota Bagger no suction

[Dave_eng]

A few comments for you before you begin using a manometer for large suction fans.

The photo I posted is the size typically used to set gas pressure for a natural gas or propane generator such a 20 KW Generac. Gas pressures are typically 7 to 20” of water.

I looked at the spec’s for a central vac for a home recently. It would suck water up 171” which is 14’ 3”.

This spec is for the vac hose completely closed off so no air is flowing.

If you have a shop vac, why not start with it first. Connect the U tube to the drain on the vac using duct tape. Now you can see real suction numbers while the unit is moving air through the hose.

My initial comment on getting 10’ of plastic tubing is incorrect and you will just suck the water out of the U tube if each leg of the U is about 48”. You need a much larger U if things are working well.

The U tube can be as small a diameter as you can find. You may have to mount it on a long 2 x 4 or a TV tower. Alternatively, a garden hose you can see through could be used.

By starting with a shop vac which is working well, you have a sense of what numbers you should see on a manometer on your leaf vac.

The style of fan impeller you have is typical of ones used on school shop central vac systems for sawdust. The design of the impeller is so that sticks and chunks of wood do not get hung up.

Here is the spec table on a portable shop sawdust extractor. The Vacuum is listed in Pa but the inches of water number would be 96”

.

I know you have already said the impeller rotation is correct. It is the fan enclosure or scroll that generates the pressure. The system is so simple.

Fan rpm is also important. By eye, your fan impeller looks to be about 12" in diameter. A fan that size rotating at 540 rpm is not going to do much.

Think of the average electric motor which runs at 1800 rpm. On a sawdust extractor unit the fan impeller is right on the end of the motor shaft

Do you have a spec page for your Kubota unit. Are the pulleys running from the pto something you can photograph so I can see their sizes.

Dave M7040

 

[Dave_eng]

IROD

Look at this setup which is very much like yours.

Note that the 540 pto speed is increased to 3,000 rpm at the fan.

If you are not having the speed on your unit boosted about 600% by the correct V belt pulleys it will never work.

Invest in a cheap strobe tachometer from Amazon. Less than $20. You will put a tiny piece of reflective tape on the rotating part and point the strobe tool at it getting an immediate rpm.

https://www.amazon.com/Digital-Phot...=1498800095&sr=8-2&keywords=strobe+tachometer

Don't even bother doing the U tube test if the rpms are not 3,000 or more

Dave M7040

 

[Irod]

IROD

Look at this setup which is very much like yours.

Note that the 540 pto speed is increased to 3,000 rpm at the fan.

If you are not having the speed on your unit boosted about 600% by the correct V belt pulleys it will never work.

Invest in a cheap strobe tachometer from Amazon. Less than $20. You will put a tiny piece of reflective tape on the rotating part and point the strobe tool at it getting an immediate rpm.

https://www.amazon.com/Digital-Phot...=1498800095&sr=8-2&keywords=strobe+tachometer

Don't even bother doing the U tube test if the rpms are not 3,000 or more

Dave M7040

Well I read the user manual 3 times trying to find the required rear pto drive speed (I thought it was 540 rpm) but all it says is to run the engine at full power. It does say the fan speed is around 2100 rpm. I checked the rear pto speed for the Kubotas that work with this vac on Tractor Data, and they are all dual speed 540/960 rpm So now I don't know if this unit needs 540 or 960... It is possible and easy to change pulleys to increase fan speed? Nuts

 

[Dave_eng]

Irod
The companies that make these units are very secretive about the parts to drive the fan.

I can find no parts drawings for the pulleys driving the fan when the pto is used..

You seem to have a manual. Can you post some of the info and parts diagram if there is one.

I did some research on the fans used by industrial sawdust equipment.

In the first image you can see the style of fan is the same as your leaf vac.

In the second chart, which really is only of use to engineers like me, shows the rpm's these 12" fans are running to get high suction.

A straight bladed fan is running above 3,000 rpms

The unit you have should almost suck the shoes off your feet if rotating fast enough.

Use your pto at the highest speed you have.

If you can remove belt covers and take pictures about what there is between the pto shaft and the shaft of the fan that would be most helpful and enable me to give you more advice.

Dave M7040

 

[Irod]

Irod
The companies that make these units are very secretive about the parts to drive the fan.

I can find no parts drawings for the pulleys driving the fan when the pto is used..

You seem to have a manual. Can you post some of the info and parts diagram if there is one.

I did some research on the fans used by industrial sawdust equipment.

In the first image you can see the style of fan is the same as your leaf vac.

In the second chart, which really is only of use to engineers like me, shows the rpm's these 12" fans are running to get high suction.

A straight bladed fan is running above 3,000 rpms

The unit you have should almost suck the shoes off your feet if rotating fast enough.

Use your pto at the highest speed you have.

If you can remove belt covers and take pictures about what there is between the pto shaft and the shaft of the fan that would be most helpful and enable me to give you more advice.

Dave M7040

Thanks Dave, I do have a manual and I'll post the drive belt pics tomorrow.

 

[Irod]

I did a bit of research today on the GCK60-76BA grass catcher, and it turns out that Kubota made three different versions with either a 5", 6" or 9" drive pulley. I have the 6" pulley. All units have a 4.5" driven pulley and the fan pulleys are 9" and 4.5". I tore the thing apart tonight and pulled the 6" pulley and will replace that with a 9" and I'm also thinking about changing the 4.5" driven pulley to a 3" which should give me a fan speed of about 3240 rpm (according to the online calculator) are my calculations correct and is that too fast?
One more question, the pto shaft is welded together and pressed on the driven pulley shaft. I want to replace this with a slide shaft to make it easier to install on the tractor pto but I'm not sure what to look for, can someone give me some info on what I need?

 

[Russell King]

If you know the fan needs to be 2100 RPM and the PTO is 540 RPM then you can see what ratio the sheave diameters should be (2100/540=3.88).

Assuming you have a 2 inch diameter sheave on the fan shaft you would need 3.88*2= 7.75 diameter sheave at the PTO shaft



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[Irod]

If you know the fan needs to be 2100 RPM and the PTO is 540 RPM then you can see what ratio the sheave diameters should be (2100/540=3.88).

Assuming you have a 2 inch diameter sheave on the fan shaft you would need 3.88*2= 7.75 diameter sheave at the PTO shaft



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Not sure of the sheave diameter, but thanks for math explanation

 

[Dave_eng]

I did a bit of research today on the GCK60-76BA grass catcher, and it turns out that Kubota made three different versions with either a 5", 6" or 9" drive pulley. I have the 6" pulley. All units have a 4.5" driven pulley and the fan pulleys are 9" and 4.5". I tore the thing apart tonight and pulled the 6" pulley and will replace that with a 9" and I'm also thinking about changing the 4.5" driven pulley to a 3" which should give me a fan speed of about 3240 rpm (according to the online calculator) are my calculations correct and is that too fast?
One more question, the pto shaft is welded together and pressed on the driven pulley shaft. I want to replace this with a slide shaft to make it easier to install on the tractor pto but I'm not sure what to look for, can someone give me some info on what I need?

Irod
It is not too fast. There will be times when you have the tractor running faster than the required rpm for a pto rpm of 540 so there is always lots of safety factor in the design.

You are going to be amazed with the drastic increase in the fan suction and you wont be going around trying to stop small air leaks. As the fan rpm's increase you suddenly notice the suction effect growing.

Your photos are interesting but because I cannot picture the belt arrangement, I am still a little confused.

Is there one or two V belts ? If my impression is correct and there are 2 V belts and two places where the rpm's are changed we need to be especially careful with your changing of pulleys!!!

Dave M7040

 

[Irod]

Irod
It is not too fast. There will be times when you have the tractor running faster than the required rpm for a pto rpm of 540 so there is always lots of safety factor in the design.

You are going to be amazed with the drastic increase in the fan suction and you wont be going around trying to stop small air leaks. As the fan rpm's increase you suddenly notice the suction effect growing.

Your photos are interesting but because I cannot picture the belt arrangement, I am still a little confused.

Is there one or two V belts ? If my impression is correct and there are 2 V belts and two places where the rpm's are changed we need to be especially careful with your changing of pulleys!!!

Dave M7040

Sorry for the confusion- yes, two drive belts. The image with two pulleys is the fan, 9" and 4.5"

 

[Russell King]

I too am confused about the belting and sheave diameters...
Please measure the outer diameter of each sheave.
Sheave 1 is the one driven by the PTO shaft, then sheave 2 is driven by the belt from sheave 1? Then sheave 3 is attached to the same shaft as sheave 2? Then sheave 4 is on the fan shaft and driven by belt from sheave 3?


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[Dave_eng]

Irod

Dont be insulted by these questions please. I am one who is prone to imagine the worst possible outcomes when I am giving advice.

The two V belts will each be part of an rpm boosting process and not knowing what Web tool you used to know final fan speed , I just am trying to be extra certain we all know with a high level of confidence the final fan speed.

Here is an illustration to describe what I picture the situation to be.

Pulley #2 will rotate the common shaft and in doing so rotate pulley #3 at the same speed.

If pulley #2 and pulley #3 are the same size, life is now more certain

If this functionally describes how shafts, pulleys and fans are interconnected, can you tell me the size of each of the pulleys using the identifying numbers #1,#2, #3, and #4 on my sketch.

Dave M7040

 

[Irod]

Irod

Dont be insulted by these questions please. I am one who is prone to imagine the worst possible outcomes when I am giving advice.

The two V belts will each be part of an rpm boosting process and not knowing what Web tool you used to know final fan speed , I just am trying to be extra certain we all know with a high level of confidence the final fan speed.

Here is an illustration to describe what I picture the situation to be.

Pulley #2 will rotate the common shaft and in doing so rotate pulley #3 at the same speed.

If pulley #2 and pulley #3 are the same size, life is now more certain

If this functionally describes how shafts, pulleys and fans are interconnected, can you tell me the size of each of the pulleys using the identifying numbers #1,#2, #3, and #4 on my sketch.

Dave M7040

Your drawing is correct, sorry for the confusion on my end.
Pulley #1 is 6" I want to change this to 9" like the GCK60-26BX
Pulley #2 is 4.5"
Pulley #3 is 9"
Pulley #4 is 4.5"
And I have one correction. I referenced the grass catcher having three different drive pulleys. The 76ba has two, a 5" or 6". The GCK60-26BX use 9" drive pulleys and 4.5" driven pulleys. Same setup as your drawing. By changing the 6" drive pulley to 9" the online calculator gave me a final drive speed of 2160 rpm, the same speed as the operating manual and that is why I thought I could use the bigger pulley. Confused?

 

[Dave_eng]

Irod
I updated the sketch with your information.

In simple terms each belt and pulley set will double the speed after you install the 9" pulley in #1 with a final fan speed of about 2360 rpm

It seems a little slow when I consider the other pto yard vac info I posted earlier which said their setup boosted their fan to 3,000 rpm.

However, if that is the speed mentioned in the Kubota literature it is where you should aim.

Once you have proven to yourself that rpm's are the answer you have saved yourself a lot of guessing.

Please let us all know the outcome.

Dave M7040

 

[Irod]

Irod
I updated the sketch with your information.

In simple terms each belt and pulley set will double the speed after you install the 9" pulley in #1 with a final fan speed of about 2360 rpm

It seems a little slow when I consider the other pto yard vac info I posted earlier which said their setup boosted their fan to 3,000 rpm.

However, if that is the speed mentioned in the Kubota literature it is where you should aim.

Once you have proven to yourself that rpm's are the answer you have saved yourself a lot of guessing.

Please let us all know the outcome.

Dave M7040

Yeah the speed seems a little low to me too.
Now for another what if-instead of changing the 6" to 9", how about changing both 4.5" to 3" ? This would give me something around 3,240 which is on par with the other brand you mentioned and the pulleys are available locally and cheaper.
Thanks for everyones help and I'll post a link to a video when this is completed

 

[Lil Foot]

Once you have proven to yourself that rpm's are the answer you have saved yourself a lot of guessing.

Agreed. On virtually every piece of equipment I have, not one speed was as listed in the manual or nomenclature plate. I bought one of these on sale for about $24 to verify rpm on all my stuff. Handy item.
https://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html

 

[Russell King]

In one BAD experience with a fan turning faster than it should l am now super cautious about how fast the fans are rated to turn. Fan manufacturers save money by building slower speed fans with less material than high speed fans. Just don't blow your fan up or you will need to repair the shroud around it and hopefully nothing else is damaged.

It is interesting that some could adjust the speed with the pto gears. Take dave_eng example and see what you get with existing sheaves and the 960 rpm input speed mentioned. The fan and sheaves may be set up for that input speed. You can adjust sheave diameters and belt length to achieve what ever fan speed is correct and safe


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[Russell King]

Dave may have made an error in calculating or writing the rpm down... I think using the 9 inch input sheave and 540 you get 540x4=2160. Dave wrote 2360 - no big deal
Using the current 6 inch input sheave and 540 you get 540(6/4.5)(9/4.5)=1440.
Using 960 input and 6 inch sheave you get 960(6/4.5)(9/4.5)=2560.
Using 960 input and 9 inch sheave you get 960(9/4.5)(9/4.5)=3840
Your calculations with 6/3 and 9/3 inch sheaves is correct at 3240


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[Dave_eng]

Irod
I should have known better than to multiply in my head. The fan rpm is 2160.

Kubota is not making leaf vac's in Japan. Their products are made by someone like Protero and painted the color of the brand of machine who wants to market the vac as an accessory.

I think you should be trying to find out who made yours.

Protero bought out Pro Vac

Q: How can I tell if my blower is a Quick Vac or a Pro Vac?

A: Protero purchased Turf Specialties. They offered a blower called the Quick Vac. It has a 3/4" shaft and the drive pulley is located on the outside of the blower. The Pro Vac has a 1" shaft with the drive pulley on the operator's side of the machine.

Once you have identified who made your machine, you are in the best place to find out the max rpm's their fans should run.

Be cautious as an exploding fan wheel will cut through the fan sheet metal enclosure very easily and can kill or blind someone.

I also maintain having a strobe tach is a prudent step especially when you see how cheap they are. Nothing like working with real numbers and not calculated ones.

Using the pulley diameter is just a crude tool to calculate speed changes.
In reality, the pulley diameter is part way down the thickness of the belt when the belt is in the pulley grove. This changes as the V belt wears and pulleys start to wear.

Dave M7040

 

[Irod]

Just a quick update. I replaced the 6" drive pulley with a 9" and a new belt.
Today was the first time I had a chance to use the vac and what a difference. The first thing I noticed was the very loud whirring sound. I always wear earmuffs but I'm probably gonna wear earplugs as well. Anyway, the thing sucks like crazy. I was able to cut thick grass and weeds moving pretty quickly without any clogs! I am very happy
Rod