I know there’s motory types in here and a few questions……..

Standard Chonda motor, 196cc 6.5 HP. Full throttle, what sorta RPM can I expect from it? Is it best to run one of these things full throttle?

I need to gear a pump (pulley and belts) at around 300 – 350 rpm for the pump.

The pulley on the pump is 18 cm radius. (114 cm circumference).

I can do the maths to get relevant pulley size for the motor if I know the max revs for full throttle.

It’s been suggested (by more than one) that I get a 2:1 reduction gearbox on the motor.

I’m asking why? What’s wrong with an appropriate sized pulley on the motor (half the circumference) to achieve a 2:1 reduction, as the gearbox would?

What is the advantage of a 2:1 reduction gearbox over an appropriate sized pulley on the motor to achieve the same thing?

stationary motor? Full revs? Not for long periods.

Woodie said:

I know there’s motory types in here and a few questions……..

Standard Chonda motor, 196cc 6.5 HP. Full throttle, what sorta RPM can I expect from it? Is it best to run one of these things full throttle?

I need to gear a pump (pulley and belts) at around 300 – 350 rpm for the pump.

The pulley on the pump is 18 cm radius. (114 cm circumference).

I can do the maths to get relevant pulley size for the motor if I know the max revs for full throttle.

It’s been suggested (by more than one) that I get a 2:1 reduction gearbox on the motor.

I’m asking why? What’s wrong with an appropriate sized pulley on the motor (half the circumference) to achieve a 2:1 reduction, as the gearbox would?

What is the advantage of a 2:1 reduction gearbox over an appropriate sized pulley on the motor to achieve the same thing?

To gear the motor, you need the reduction. To gear straight off the motor, don’t be surprised if it pops things out sideways.

BTW, this is the pump.

pump

Woodie said:

BTW, this is the pump.

pump

Oh….. Without motor.

Woodie said:

BTW, this is the pump.

pump

If that is an exact description of your pump.. it looks already assembled to tackle the task. Why do you want to change it?

Woodie said:

Woodie said:

BTW, this is the pump.

pump

Oh….. Without motor.

Ah.. Do you have the stats on the motor in the photo? or do I have to look at the photo again?

roughbarked said:

stationary motor? Full revs? Not for long periods.

I run the mower at full throttle (push mower, ride on, and zero turn). Doesn’t everyone?

Woodie said:

roughbarked said:

stationary motor? Full revs? Not for long periods.

I run the mower at full throttle (push mower, ride on, and zero turn). Doesn’t everyone?

Not for long periods carrying load..

your motor in the image is a Honda GX 120

So yours (195)should be ample.

roughbarked said:

Woodie said:

Woodie said:

BTW, this is the pump.

pump

Oh….. Without motor.

Ah.. Do you have the stats on the motor in the photo? or do I have to look at the photo again?

standard 6.5 hp Honda. It went on another pump. I’ve just bought the pump only. Will be putting a 6.5 HP Chonda on it. I don’t know the pulley size on the motor in the pics.

roughbarked said:

Woodie said:

roughbarked said:

stationary motor? Full revs? Not for long periods.

I run the mower at full throttle (push mower, ride on, and zero turn). Doesn’t everyone?

Not for long periods carrying load..

your motor in the image is a Honda GX 120

So yours (195)should be ample.

It’s the gearing I need. Appropriate pulley size for the motor to get 300 – 350 rpm on the pump. motor guts on a 6.5 hp is not a problem. It’s the revs and gearing.

Woodie said:

roughbarked said:

Woodie said:

Oh….. Without motor.

Ah.. Do you have the stats on the motor in the photo? or do I have to look at the photo again?

standard 6.5 hp Honda. It went on another pump. I’ve just bought the pump only. Will be putting a 6.5 HP Chonda on it. I don’t know the pulley size on the motor in the pics.

You know the ratio though. You measure what is on the motor and apply the ratio. Buy that pulley and connect it via a belt.

Full revs is around 3500, but you would be better off running it at around 2500RPM. (two thirds throttle)

Woodie said:

roughbarked said:

Woodie said:

I run the mower at full throttle (push mower, ride on, and zero turn). Doesn’t everyone?

Not for long periods carrying load..

your motor in the image is a Honda GX 120

So yours (195)should be ample.

It’s the gearing I need. Appropriate pulley size for the motor to get 300 – 350 rpm on the pump. motor guts on a 6.5 hp is not a problem. It’s the revs and gearing.

Ideally when pulling loads, you want your best gearing at 3/4 revs.

Most quote this sorta thing.

MAXIMUM POWER OUTPUT – 6.5hp @ 3600rpm

MAXIMUM TORQUE OUTPUT – 13.0 N.m @ 2500rpm

however, is 3600 rpm half throttle or full throttle???

Ya see, if I get the revs wrong, and it runs at 6000 rpm, but I calc for 3500 rpm to get 350 rpm at the pump, at 6000 rpm on the motor it’ll blow the pipes up, and the pump is not designed for 600 rpm at the pump!. Max design revs on the pump is 350 rpm.

From looking at the web the RPM for that motor is ~3600 Woodie.
If you run it through a gearbox you’d want a clutch as well I’d imagine.
A clutch would be good for starting the engine.
I’ve got something similar on the redoubt.
How much lift does that pump have?

Peak Warming Man said:

From looking at the web the RPM for that motor is ~3600 Woodie.
If you run it through a gearbox you’d want a clutch as well I’d imagine.
A clutch would be good for starting the engine.
I’ve got something similar on the redoubt.
How much lift does that pump have?

A slipping belt is a clutch.

roughbarked said:

Woodie said:

roughbarked said:

Not for long periods carrying load..

your motor in the image is a Honda GX 120

So yours (195)should be ample.

It’s the gearing I need. Appropriate pulley size for the motor to get 300 – 350 rpm on the pump. motor guts on a 6.5 hp is not a problem. It’s the revs and gearing.

Ideally when pulling loads, you want your best gearing at 3/4 revs.

or what Kingy said.. 2/3

Peak Warming Man said:

From looking at the web the RPM for that motor is ~3600 Woodie.
If you run it through a gearbox you’d want a clutch as well I’d imagine.
A clutch would be good for starting the engine.
I’ve got something similar on the redoubt.
How much lift does that pump have?

I have about a 300 m traverse with a 40 m head. Stats on the Ajax A3 is up to 600 ft head. Delivers 825 g/ph (3700 l/ph) at 350 rpm. 1 1/2 in outlet, but I have 1 1/4 in feed up the hill, so I’m going to have to slow it down a bit anyway.

Woodie said:

Peak Warming Man said:

From looking at the web the RPM for that motor is ~3600 Woodie.
If you run it through a gearbox you’d want a clutch as well I’d imagine.
A clutch would be good for starting the engine.
I’ve got something similar on the redoubt.
How much lift does that pump have?

I have about a 300 m traverse with a 40 m head. Stats on the Ajax A3 is up to 600 ft head. Delivers 825 g/ph (3700 l/ph) at 350 rpm. 1 1/2 in outlet, but I have 1 1/4 in feed up the hill, so I’m going to have to slow it down a bit anyway.

Anyway.. I presume you have already put the motor on the pump and tested it. And that you now want to change the gearing?

Peak Warming Man said:

From looking at the web the RPM for that motor is ~3600 Woodie.
If you run it through a gearbox you’d want a clutch as well I’d imagine.
A clutch would be good for starting the engine.
I’ve got something similar on the redoubt.
How much lift does that pump have?

2:1 reduction and clutch adds $140 to the motor price ($150 v/s $280)

roughbarked said:

Woodie said:

Peak Warming Man said:

From looking at the web the RPM for that motor is ~3600 Woodie.
If you run it through a gearbox you’d want a clutch as well I’d imagine.
A clutch would be good for starting the engine.
I’ve got something similar on the redoubt.
How much lift does that pump have?

I have about a 300 m traverse with a 40 m head. Stats on the Ajax A3 is up to 600 ft head. Delivers 825 g/ph (3700 l/ph) at 350 rpm. 1 1/2 in outlet, but I have 1 1/4 in feed up the hill, so I’m going to have to slow it down a bit anyway.

Anyway.. I presume you have already put the motor on the pump and tested it. And that you now want to change the gearing?

Yet to get the motor and motor pulley. That’s why I asking 2:1 reduction gearbox, or just use appropriate sized pulley on the motor instead.

Woodie said:

roughbarked said:

Woodie said:

I have about a 300 m traverse with a 40 m head. Stats on the Ajax A3 is up to 600 ft head. Delivers 825 g/ph (3700 l/ph) at 350 rpm. 1 1/2 in outlet, but I have 1 1/4 in feed up the hill, so I’m going to have to slow it down a bit anyway.

Anyway.. I presume you have already put the motor on the pump and tested it. And that you now want to change the gearing?

Yet to get the motor and motor pulley. That’s why I asking 2:1 reduction gearbox, or just use appropriate sized pulley on the motor instead.

A reduction is simply another pulley. This can be on the pump or between. The drive pulley on the motor is the manufacturers specification. Technically, it should be left as is.

This one at the redoubt has a discharge bypass line with a vale back into the dam.
I’m guessing that is there to make starting easier, might be hard to hand start the engine against a 50m head.
However I’ve never started it, it needs a good service.

Woodie said:

What is the advantage of a 2:1 reduction gearbox over an appropriate sized pulley on the motor to achieve the same thing?

BTW, this is the pump.

pump

Oh, piston pump. I’ve only once seen one of those operating close up. Actually no, it was a completely different piston arrangement, you’re on your own. The image below is the only type of piston pump I’ve dealt with, not the same as yours.

Pulley vs gearbox. Always noisier, shorter lifespan and greater energy loss with the pulley. But apart from that, well, why not? I’ve never been near a pump driven by a pulley, either.

What’s the torque on this piston pump? Any ideas?

Peak Warming Man said:

This one at the redoubt has a discharge bypass line with a vale back into the dam.
I’m guessing that is there to make starting easier, might be hard to hand start the engine against a 50m head.
However I’ve never started it, it needs a good service.

firteen horses! Fernerkle dergle! Wadda ya pumpin’? Sydney harbour fulls?

mollwollfumble said:

What’s the torque on this piston pump? Any ideas?

I don’t think torque on a pump is a spec, is it?

Just done more sums.

10:1 reduction @ 3500 rpm motor to get 350 rpm at the pump.

Pump has 18cm radius pulley (114 cm circumference). that means a 34mm (diameter) pulley on the motor to get 10:1. That’s a tiny pulley. Don’t think they make them that small..

Hence the 2:1 reduction Gearbox. 5:1 reduction of 1750 rpm motor to get 350 rpm at the pump means 72 mm pulley on the motor. Yep. They make 70mm pulleys.

Maybe that’s why the 2:1 reduction gearbox. Can’t get 34mm pulleys to go on a 19mm shaft.

Are my sums correct?

Peak Warming Man said:

This one at the redoubt has a discharge bypass line with a vale back into the dam.
I’m guessing that is there to make starting easier, might be hard to hand start the engine against a 50m head.
However I’ve never started it, it needs a good service.

You should have a non-return valve on the pump outlet. It will also stop the water running back through the pump.

PermeateFree said:

Peak Warming Man said:

This one at the redoubt has a discharge bypass line with a vale back into the dam.
I’m guessing that is there to make starting easier, might be hard to hand start the engine against a 50m head.
However I’ve never started it, it needs a good service.

You should have a non-return valve on the pump outlet. It will also stop the water running back through the pump.

You still have to push the head, non return valve or not.

Here’s a nice little ready reckoner.

http://www.blocklayer.com/pulley-belt.aspx

Peak Warming Man said:

PermeateFree said:

Peak Warming Man said:

This one at the redoubt has a discharge bypass line with a vale back into the dam.
I’m guessing that is there to make starting easier, might be hard to hand start the engine against a 50m head.
However I’ve never started it, it needs a good service.

You should have a non-return valve on the pump outlet. It will also stop the water running back through the pump.

You still have to push the head, non return valve or not.

I open another valve which allows water to go through the pump at zero head. When everything is warmed up & running smoothly I open the line to the head tank (55m lift) & slowly close the zero head valve.

Peak Warming Man said:

Here’s a nice little ready reckoner.

http://www.blocklayer.com/pulley-belt.aspx

According to your gonkulator, Mr Man, my sums look pretty close.

just keep in mind that reduction of pulley size reduces (necessary) pulley/belt friction.

probably why sometimes a reduction box is used, you can use a bigger pulley. Other thing about small pulleys is they take they V-belt around a tighter radius, which increases heating (too, as does slip), and variously the flex reduces the life of the belt.

pulleys wear out too, so smaller the pulley…….you get the idea.

I fink I’ve funcked me finkin’ and done me sums properly as to why I’ve been told to get a 2:1 reduction gearbox on the motor..

No reduction gearbox, I’d need a 34mm pulley on the motor to get 350 rpm at the pump 3500 rpm the motor.

They don’t make pulleys that small for a 19mm motor shaft.

2:1 reduction gearbox mean 70 mm pulley at the motor to get 350 rpm at the pump. They do make 70 mm pulleys.

Mr Man’s pulley gonkulator confirmed my sums. Fax for the link Mr Man. :)

To quote Inspector Clouseau “Le proberlem eez solve-ed” :)

Woodie said:

I fink I’ve funcked me finkin’ and done me sums properly as to why I’ve been told to get a 2:1 reduction gearbox on the motor..

No reduction gearbox, I’d need a 34mm pulley on the motor to get 350 rpm at the pump 3500 rpm the motor.

They don’t make pulleys that small for a 19mm motor shaft.

2:1 reduction gearbox mean 70 mm pulley at the motor to get 350 rpm at the pump. They do make 70 mm pulleys.

Mr Man’s pulley gonkulator confirmed my sums. Fax for the link Mr Man. :)

To quote Inspector Clouseau “Le proberlem eez solve-ed” :)

Or increase the size of both pulleys.

1 1/2 in outlet, but I have 1 1/4 in feed up the hill, so I’m going to have to slow it down a bit anyway.

—————-

When I moved here the line from the spear/firefighter at the creek to the top tank was half and half 1 1/2 in and 1 1/4 in. The previous owner said he’d made a mistake not going with 1 1/2 in for the lot.. makes a big difference.

Later on I laid 1 1/2 in for the whole run and it made a big difference… (Don’t how relevant that is to this discussion)

Ian said:

1 1/2 in outlet, but I have 1 1/4 in feed up the hill, so I’m going to have to slow it down a bit anyway.

—————-

When I moved here the line from the spear/firefighter at the creek to the top tank was half and half 1 1/2 in and 1 1/4 in. The previous owner said he’d made a mistake not going with 1 1/2 in for the lot.. makes a big difference.

Later on I laid 1 1/2 in for the whole run and it made a big difference… (Don’t how relevant that is to this discussion)

Might be relevant if you don’t have to run the motor at full revs due to reduced friction head.

i’m dumb on pumps, what is it a piston pump?

transition said:

i’m dumb on pumps, what is it a piston pump?

An engine driven piston inside a cylinder.
Piston at top, inlet &outlet valves closed, inlet valve opens. Piston moves down, sucks water into cylinder.
Piston at bottom, inlet valve closes, outlet valve opens. Piston moves up, forces water out of cylinder & up hill.

Tamb said:

transition said:

i’m dumb on pumps, what is it a piston pump?

An engine driven piston inside a cylinder.
Piston at top, inlet &outlet valves closed, inlet valve opens. Piston moves down, sucks water into cylinder.
Piston at bottom, inlet valve closes, outlet valve opens. Piston moves up, forces water out of cylinder & up hill.

few different diplacement units, could be a regular piston looking thing, or plunger, wouldn’t be high rpm

probably need good drive friction on ya pulleys, even with the multiple v-belts

transition said:

Tamb said:

transition said:

i’m dumb on pumps, what is it a piston pump?

An engine driven piston inside a cylinder.
Piston at top, inlet &outlet valves closed, inlet valve opens. Piston moves down, sucks water into cylinder.
Piston at bottom, inlet valve closes, outlet valve opens. Piston moves up, forces water out of cylinder & up hill.

few different diplacement units, could be a regular piston looking thing, or plunger, wouldn’t be high rpm

probably need good drive friction on ya pulleys, even with the multiple v-belts

Plunger types can only lift to about 9 metres (1 atmosphere)

Peak Warming Man said:

PermeateFree said:

Peak Warming Man said:

This one at the redoubt has a discharge bypass line with a vale back into the dam.
I’m guessing that is there to make starting easier, might be hard to hand start the engine against a 50m head.
However I’ve never started it, it needs a good service.

You should have a non-return valve on the pump outlet. It will also stop the water running back through the pump.

You still have to push the head, non return valve or not.

Not if the valve is holding back the head. The valve can be fitted further away from the pump to create an empty space between the pump and the valve. Once fitted there is no need to worry about it.

PermeateFree said:

Peak Warming Man said:

PermeateFree said:

You should have a non-return valve on the pump outlet. It will also stop the water running back through the pump.

You still have to push the head, non return valve or not.

Not if the valve is holding back the head. The valve can be fitted further away from the pump to create an empty space between the pump and the valve. Once fitted there is no need to worry about it.

Read my post on the two valves. One at head pressure & one at zero pressure.

Ian said:

Later on I laid 1 1/2 in for the whole run and it made a big difference… (Don’t how relevant that is to this discussion)

BIG diff according to Mr Irrigation man. eg. Ajax A2 pump has 1 1/4 in outlet. at 350 rpm delivers 420 g/ph. Ajax A3 pump has 1 1/2 in outlet and delivers 825 g/ph at 350 rpm. Almost twice the delivery rate.

Mr Irrigation man suggests I’ll have to run at max 250 rpm (590 g p/hr), if I keep the 1 1/4 in delivery pipe.

transition said:

i’m dumb on pumps, what is it a piston pump?

One of these.

pump

Tamb said:

PermeateFree said:

Peak Warming Man said:

You still have to push the head, non return valve or not.

Not if the valve is holding back the head. The valve can be fitted further away from the pump to create an empty space between the pump and the valve. Once fitted there is no need to worry about it.

Read my post on the two valves. One at head pressure & one at zero pressure.

Sure that will work too, but a non-return valve will do the same job automatically. I draw water from a bore 60 odd feet deep and pump it nearly 200 metres to an elevation of 30-40 ft. I have a non-return valve at the tank to which I pump. This not only stops the tank water running back to the bore, but creates a 200 metre section of low pressure, where I can start the pump with no problems.

Might have to do an intermediate pulley system.

say 5:1 then 2:1

ChrispenEvan said:

Might have to do an intermediate pulley system.

say 5:1 then 2:1

the cost of replacing the polypipe would be pretty high for 300m.

Tamb said:

transition said:

Tamb said:

An engine driven piston inside a cylinder.
Piston at top, inlet &outlet valves closed, inlet valve opens. Piston moves down, sucks water into cylinder.
Piston at bottom, inlet valve closes, outlet valve opens. Piston moves up, forces water out of cylinder & up hill.

few different diplacement units, could be a regular piston looking thing, or plunger, wouldn’t be high rpm

probably need good drive friction on ya pulleys, even with the multiple v-belts

Plunger types can only lift to about 9 metres (1 atmosphere)

Some years ago I had one of those piston pumps, got it from a company called Southern Cross in Victoria. It looked like its design was at least 100 years old, but I think they still look much the same today. It was not good at lifting water, but could pump it as far as you want. It was difficult to start even if it had a small head of water to push.

piston pumps are positive displacement pumps. if you have the HP and the pipe can take the pressure you can pump to any height. all pumps that rely on suction wont lift over around 9m on the suction side. that is why bore pumps are used on bores deeper than 9m.

ChrispenEvan said:

piston pumps are positive displacement pumps. if you have the HP and the pipe can take the pressure you can pump to any height. all pumps that rely on suction wont lift over around 9m on the suction side. that is why bore pumps are used on bores deeper than 9m.

those bore pumps that fit down the bore that is, they are PD pumps.

ChrispenEvan said:

ChrispenEvan said:

Might have to do an intermediate pulley system.

say 5:1 then 2:1

the cost of replacing the polypipe would be pretty high for 300m.

Cost of pipe is minimal. It’s getting trenched and backfilled is pricey.

ChrispenEvan said:

piston pumps are positive displacement pumps. if you have the HP and the pipe can take the pressure you can pump to any height. all pumps that rely on suction wont lift over around 9m on the suction side. that is why bore pumps are used on bores deeper than 9m.

You can go a little deeper with a Venturi Pump Assembly .

Woodie said:

ChrispenEvan said:

ChrispenEvan said:

Might have to do an intermediate pulley system.

say 5:1 then 2:1

the cost of replacing the polypipe would be pretty high for 300m.

Cost of pipe is minimal. It’s getting trenched and backfilled is pricey.

how much do you reckon 300m of 40 mm pipe is?

another way would be two feed lines. keep the old one and add an extra one. large tee joint at pump feeding the two smaller lines.

PermeateFree said:

ChrispenEvan said:

piston pumps are positive displacement pumps. if you have the HP and the pipe can take the pressure you can pump to any height. all pumps that rely on suction wont lift over around 9m on the suction side. that is why bore pumps are used on bores deeper than 9m.

You can go a little deeper with a Venturi Pump Assembly .

28’ from what i have read. whatever that is in metres. plain centrifugal wouldn’t do 9m anyway. maybe 7.

ChrispenEvan said:

Woodie said:

ChrispenEvan said:

the cost of replacing the polypipe would be pretty high for 300m.

Cost of pipe is minimal. It’s getting trenched and backfilled is pricey.

how much do you reckon 300m of 40 mm pipe is?

another way would be two feed lines. keep the old one and add an extra one. large tee joint at pump feeding the two smaller lines.

The most commonly used water pipe: 1 1/4” Rural Green Stripe Poly Pipe x 150m coil – rated to 800 kPa – 2 Pack

1 1/4” Rural Green Stripe Poly Pipe x 150m coil – rated to 800 kPa – 2 Pack

Rural “Green Stripe” PE100 PN 8 polyethylene pipe is measured internally (the ID) and is suitable for water transfer, irrigation, stock watering systems and any other general low pressure pumping or gravity feed application where the pressure in the system will never exceed 800 kPa. This pipe is not suitable for pump suction lines and metric poly should be used on all pump suction lines. Supplied in neat coils with plastic strap ties and easily visible specifications on the pipe. For Plasson rural fittings click here. We supply Vinidex brand depending on product availability and your location. Supplied in multiples of 2 coils, an inner and outer coil with a total measurement of 1660mm diameter and 270mm width – 59kg
Price:

$464.50
inc GST within Australia

ChrispenEvan said:

PermeateFree said:

ChrispenEvan said:

piston pumps are positive displacement pumps. if you have the HP and the pipe can take the pressure you can pump to any height. all pumps that rely on suction wont lift over around 9m on the suction side. that is why bore pumps are used on bores deeper than 9m.

You can go a little deeper with a Venturi Pump Assembly .

28’ from what i have read. whatever that is in metres. plain centrifugal wouldn’t do 9m anyway. maybe 7.

I pump at the surface from a bore drilled to 66 ft, however the water comes up quite a bit, but is just below the maximum centrifugal pump capability, but with a Venturi fitted I could do it easily and have never had a problem.

PermeateFree said:

ChrispenEvan said:

PermeateFree said:

You can go a little deeper with a Venturi Pump Assembly .

28’ from what i have read. whatever that is in metres. plain centrifugal wouldn’t do 9m anyway. maybe 7.

I pump at the surface from a bore drilled to 66 ft, however the water comes up quite a bit, but is just below the maximum centrifugal pump capability, but with a Venturi fitted I could do it easily and have never had a problem.

no suction pump will lift beyond what the atmospheric pressure is. quite a bit less. jet pumps do to 9m. you wont get 10 metres lift. that is why i mentioned 9m for jet and about 7m for plain centrifugal.

ChrispenEvan said:

PermeateFree said:

ChrispenEvan said:

28’ from what i have read. whatever that is in metres. plain centrifugal wouldn’t do 9m anyway. maybe 7.

I pump at the surface from a bore drilled to 66 ft, however the water comes up quite a bit, but is just below the maximum centrifugal pump capability, but with a Venturi fitted I could do it easily and have never had a problem.

no suction pump will lift beyond what the atmospheric pressure is. quite a bit less. jet pumps do to 9m. you wont get 10 metres lift. that is why i mentioned 9m for jet and about 7m for plain centrifugal.

A deep well jet pump combines two principles of pumping – that of the centrifugal pump and that of an injector (nozzle and venturi assembly).

Davey’s range of deep well pumps are fitted with a pressure switch for easy conversion to automatic operation.

An automatic demand response valve (ADR) is fitted as standard to protect against loss of prime from over pumping.

Used in conjunction with Deep Well injector kits, these pumps are ideal for supplying high pressure water from bores to 42m depth for:

• Water supply

• Tank filling

• Stock watering

• Sprinkler supply

Pumps can also be used in applications where the pump needs to be horizontally offset from the water supply.

Why oh why do I research this stuff too much!

I fink me sums are up the creek.

When using V pulleys and V belts, What diameter should I use for calcamalating gearing ratios?

The full pulley diameter? or the diameter at the base of the V? A 90mm pulley has a 10 mm V depth. That make 70 mm diameter at the depth of the V.

If I use the base of the V (70mm) I get 340 rpm at the pump.
If I use the full diameter (90 mm) at the outer rim I get 437 rpm at the pump.

340 is just ok, (350 max) but 437 is too much for the pump.

Where are all you mathermermatical and fizzicks types? To V or not to V? That is my question.

http://www.smex.net.au/reference/Vbelts02.php

The size of a pulley is indicated by its pitch diameter (D), which slightly smaller than the outside measured diameter. The centre distance between the shafts is indicated as C in the diagram.

so a 90mm pulley is measured at the pitch and will be the correct measurement to use. from what i gather.

ChrispenEvan said:

http://www.smex.net.au/reference/Vbelts02.php

The size of a pulley is indicated by its pitch diameter (D), which slightly smaller than the outside measured diameter. The centre distance between the shafts is indicated as C in the diagram.

so a 90mm pulley is measured at the pitch and will be the correct measurement to use. from what i gather.

Useful info. hmmmmmmm….. “pitch diameter”.

Woodie:

The standard for stationary engines is 3000 rpm for petrol and 1500 rpm for diesel (yeah I know, irrelevant). So do your calculations for 3000 rpm. You can go a bit less or a bit more if necessary when it is set up. But do the calcs for 3000 rpm. That is not necessarily full throttle, it’s a governed speed.

(Note 1: although you might set the throttle to Max, the governor reduces the butterfly opening in the carby if the load is less than maximum)
(Note 2: The governor is adjustable, but it’s finicky)
(Note 3: Max Torque 2500 rpm, Max HP 3600 rpm, so ideal speeds are within this range)

Pulley sizes: very small to very large pulleys is not a Good Thing. Small pulleys induce belt wear, and also belts will need to be tighter, because the belt grip length is small. So a reduction gearbox is your friend.

Now, I need to go look at your specs to check your calculations.

Woodie said:

I know there’s motory types in here and a few questions……..

Standard Chonda motor, 196cc 6.5 HP. Full throttle, what sorta RPM can I expect from it? Is it best to run one of these things full throttle?

I need to gear a pump (pulley and belts) at around 300 – 350 rpm for the pump.

The pulley on the pump is 18 cm radius. (114 cm circumference).

I can do the maths to get relevant pulley size for the motor if I know the max revs for full throttle.

It’s been suggested (by more than one) that I get a 2:1 reduction gearbox on the motor.

I’m asking why? What’s wrong with an appropriate sized pulley on the motor (half the circumference) to achieve a 2:1 reduction, as the gearbox would?

What is the advantage of a 2:1 reduction gearbox over an appropriate sized pulley on the motor to achieve the same thing?

With a 2:1 reduction gearbox:

Output shaft = 1500 rpm (standard)
Pump pulley = 36cm dia.
Ideal pump speed = 300 rpm.
Pulley reduction = 1:5

So: Small pulley diameter = 36/5 cm. So 7.2 cm exactly is what’s required for 300 pump rpm.

Now, 7 cm Pump Pulley or 7.5 cm pulley? (I’ll assume these two sizes are available.)

7.0 cm: 1500 rpm * 7.0 / 36 = 292 rpm at pump. OK
7.5 cm: 1500 rpm * 7.5 / 36 = 312 rpm at pump. OK

Also, check 8.0 cm, and 8.5 cm as the range quoted was 300 – 350 pump rpm

8.0 cm: 1500 rpm * 8.0 / 36 = 333 rpm at pump. OK
8.5 cm: 1500 rpm * 8.5 / 36 = 354 rpm at pump. OK

Woodie said:

Just done more sums.

10:1 reduction @ 3500 rpm motor to get 350 rpm at the pump.

Pump has 18cm radius pulley (114 cm circumference). that means a 34mm (diameter) pulley on the motor to get 10:1. That’s a tiny pulley. Don’t think they make them that small..

Hence the 2:1 reduction Gearbox. 5:1 reduction of 1750 rpm motor to get 350 rpm at the pump means 72 mm pulley on the motor. Yep. They make 70mm pulleys.

Maybe that’s why the 2:1 reduction gearbox. Can’t get 34mm pulleys to go on a 19mm shaft.

Are my sums correct?

Yes, the way you are working stuff out is correct. A 2:1 reduction from 3000 engine rpm, gives 1500 rpm output shaft rpm.