Hydraulic Flow Rate Chart

NHSleddog · Feb 24, 2020

Does anyone have a link to a good hydraulic flow rate chart?

Specifically I am looking at what will flow through 1/4, 3/8, 1/2 hose (gpm) at a specific pressure.

Fluke631 · Feb 26, 2020

I always use something like the attached pic.

Dave_eng · Feb 27, 2020

The chart Fluke provided is an excellent one.

It does not answer your specific question because there are more relevant issues to fluid flow through hoses....... namely velocity (aka speed.)

The velocity part of the chart contains recommended bands of velocities for various purposes. Suction, return and pressure.

With an increase in velocity comes pressure loss, risk of damage to hose internals and, for suction lines, risk of cavitation which is when the hydraulic fluid starts to vaporize under the vacuum pulling the fluid through the hose.

If you would provide more specifics on your application, it would help better provide you with information.

Dave

NHSleddog · Feb 27, 2020

To be specific, it is hydraulic fluid.

What is the GPM through 1' of 1/4" hose at 2500psi
What is the GPM through 1' of 3/8" hose at 2500psi
What is the GPM through 1' of 1/2" hose at 2500psi

Thanks.

GreensvilleJay · Feb 27, 2020

re: 1/4" hose..

You need to understand that while the hose may be 1/4" ID, the fittings are NOT ! That WILL affect the flow and GPM capabilty. Also every fitting, say a 90* elbow also affects the 'numbers'...
There are several hydraulic websites that you can 'fill in the blanks' to get the 'numbers'....
perhaps google 'hydraulic flow rate vs PSI' ??

GeoHorn · Feb 27, 2020

That chart ignores an important factor known as “pressure”.

NHSleddog · Feb 27, 2020

GreensvilleJay said:
re: 1/4" hose..

You need to understand that while the hose may be 1/4" ID, the fittings are NOT ! That WILL affect the flow and GPM capabilty. Also every fitting, say a 90* elbow also affects the 'numbers'...
There are several hydraulic websites that you can 'fill in the blanks' to get the 'numbers'....
perhaps google 'hydraulic flow rate vs PSI' ??

Do you have a link to any of them that will answer this question? I have been looking.

The reason I said 1' of hose was to eliminate any discussion of connector, turn, length etc. Just a simple 1' of hose hanging off the pump into open air at sea level.

Dave_eng · Feb 27, 2020

If you accept that the hydraulic pump on your tractor is a positive displacement one........ meaning for each revolution of the pump a fixed and constant volume of oil will be moved, then the pump discharge conditions are insignificant absent the discharge being blocked.

A 10 liter per minute pump will discharge 10 liters per minute through all three hose sizes you mention.

As the hose size is reduced, the pump pressure will start to rise but the volume discharged will remain the same. The pump will not develop pressure until there is a resistance to flow which occurs as the velocity of the flow in the hose increases.

At some point, the pump pressure will rise to the point of tripping the pressure relief valve assuming there is one in the system.

Dave

NHSleddog · Feb 27, 2020

Dave_eng said:
If you accept that the hydraulic pump on your tractor is a positive displacement one........ meaning for each revolution of the pump a fixed and constant volume of oil will be moved, then the pump discharge conditions are insignificant absent the discharge being blocked.

A 10 liter per minute pump will discharge 10 liters per minute through all three hose sizes you mention.

As the hose size is reduced, the pump pressure will start to rise but the volume discharged will remain the same. The pump will not develop pressure until there is a resistance to flow which occurs as the velocity of the flow in the hose increases.

At some point, the pump pressure will rise to the point of tripping the pressure relief valve assuming there is one in the system.

Dave

I am not understanding.

Make believe there is no pump. Just a 1' hose with 2500psi pressure behind it.

What is the GPM through 1' of 1/4" hose at 2500psi
What is the GPM through 1' of 3/8" hose at 2500psi
What is the GPM through 1' of 1/2" hose at 2500psi

Dave_eng · Feb 27, 2020

Your question makes no sense in a practical way but nevertheless:

I used 1 meter of hose as the formula is metric.:

1/2" dia or 12.5 mm will flow 194 l per minute (51 gpm)from 2,500 psi or 172 bar
3/8" dia or 8.25 mm will flow 36 l per minute (9.5 gpm)
1/4" dia or 6.35 mm will flow 5.2 l per minute (1.37 gpm)

https://www.copely.com/tools/flow-rate-calculator/

Dave

NHSleddog · Feb 27, 2020

Dave_eng said:
Your question makes no sense in a practical way but nevertheless:

I used 1 meter of hose as the formula is metric.:

1/2" dia or 12.5 mm will flow 194 l per minute (51 gpm)from 2,500 psi or 172 bar
3/8" dia or 8.25 mm will flow 36 l per minute (9.5 gpm)
1/4" dia or 6.35 mm will flow 5.2 l per minute (1.37 gpm)

https://www.copely.com/tools/flow-rate-calculator/

Dave

To me though it makes perfect sense and I am really glad you were able to help. If those numbers are right, it will change how I plumb an auger project coming up.

On a B2650, how do you get 5GPM on the front remotes, if it is going through 1/4" hose (soft and solid with fittings)? If they are actually seeing 1.37 GPM at the factory remotes, it is no wonder they can't get a decent RPM on an auger. An actual 5GPM would be more than double that. It looks like 3/8" would be ideal.

Dave_eng · Feb 28, 2020

NHSleddog said:
To me though it makes perfect sense and I am really glad you were able to help. If those numbers are right, it will change how I plumb an auger project coming up.

On a B2650, how do you get 5GPM on the front remotes, if it is going through 1/4" hose (soft and solid with fittings)? If they are actually seeing 1.37 GPM at the factory remotes, it is no wonder they can't get a decent RPM on an auger. An actual 5GPM would be more than double that. It looks like 3/8" would be ideal.

Could you please clarify what you mean by "Front Remotes."

Do you have a loader?

The pump spec's ( loader + 3 pt) say 4.49 US GPM. If you used a 10" diameter hose you would not get more than 4.49 gpm out the end.

Dave

NHSleddog · Feb 28, 2020

Dave_eng said:
Could you please clarify what you mean by "Front Remotes."

Do you have a loader?

The pump spec's ( loader + 3 pt) say 4.49 US GPM. If you used a 10" diameter hose you would not get more than 4.49 gpm out the end.

Dave

And if you had several feet of 1/4" hose with fittings and bends, you would get at best, 1.37GPM?

The Kubota factory remotes on the front, mounted to the FEL.

GreensvilleJay · Feb 28, 2020

With 'hydraulics', bigger is better, with respect to hose diameters. A larger hose will allow for greater cooling, less friction and more capacity. Something like an 'auger' sounds like it needs a constant high volume of oil unlike a snowplow lift. This 'auger' probably has a hydraulic motor, so the 'specs' for it MUST be known, you can then design from that, keeping in mind that if using the tractor's 'system' you have to SHARE the oil and add oil to the tank to replace the oil in the auger system( hoses,motor, etc.)

Dave_eng · Feb 28, 2020

NHSleddog said:
And if you had several feet of 1/4" hose with fittings and bends, you would get at best, 1.37GPM?

The Kubota factory remotes on the front, mounted to the FEL.

I have failed in explaining that with a positive displacement pump, you have to get the full pump displacement with each revolution of the pump shaft.

Unlike a centrifugal well pump or sump pump where the output will vary based upon the resistance (i.e. head) on the discharge, a positive displacement pump does not work like that.

Yes there will be more pressure loss in the small pipe but the same quantity of fluid has to flow.

Block the outlet of a positive displacement pump and the pump will immediately fail. Either the pump body will split or the drive shaft will fail.

Block the outlet on a centrifugal well pump or sump pump and the pump will be quite happy and actually draw less power.

Where are you getting the front remote flow number?

Dave

NHSleddog · Feb 28, 2020

Dave_eng said:
.... Where are you getting the front remote flow number?
Dave

LOL I have been asking that for a month now a hundred different ways. 5GPM is a guess. Nobody knows what it actually is. I suppose Kubota knows but they have actually been changing the specs down on my model recently.

8.7 GPM gross, 3.7 GPM for power steering leaving 5. In use I will not be driving around while while digging holes so I should have close to the 5 available.

Dave_eng · Feb 28, 2020

NHSleddog said:
LOL I have been asking that for a month now a hundred different ways. 5GPM is a guess. Nobody knows what it actually is. I suppose Kubota knows but they have actually been changing the specs down on my model recently.

8.7 GPM gross, 3.7 GPM for power steering leaving 5. In use I will not be driving around while while digging holes so I should have close to the 5 available.

There are two hydraulic pumps on your tractor so the combined number really is meaningless for your purposes. The two pump flows are independent.

With an open center system, you have the full flow of the main pump available which is 4.49 US GPM at full rpm's. This is an idealized figure and likely not achieved under normal operation but will be close.

This flow figure is from the WSM.

Anything you do with the loader while the auger is working will subtract from the flow available momentarily.

Do you have any details on the hydraulic motor?

Dave

North Idaho Wolfman · Feb 28, 2020

Let me see if i can muddy the waters even more.

NHSleddog,
You're basing you 1/4" flow numbers on a 2500 psi of back pressure, hydraulic motors are not like cylinders, you do not get the same back pressure when the motor is spinning, it will be far less.

You can run any motor that you want on 1/4 line at 5 gpm, your not going to over do flow on the line.

Would 1/2" be better? No, not really as you'll never have enough flow to out do the capable volume of the line.

NHSleddog · Feb 28, 2020

North Idaho Wolfman said:
Let me see if i can muddy the waters even more.

NHSleddog,
You're basing you 1/4" flow numbers on a 2500 psi of back pressure, hydraulic motors are not like cylinders, you do not get the same back pressure when the motor is spinning, it will be far less.

You can run any motor that you want on 1/4 line at 5 gpm, your not going to over do flow on the line.

Would 1/2" be better? No, not really as you'll never have enough flow to out do the capable volume of the line.

If the pressure was going to be even less wouldn't the GPM go down? The 1.37 GPM from the chart isn't accurate?

So what is the accurate number? How many GPM will flow through that 1/4" hose?

NHSleddog · Feb 28, 2020

Dave_eng said:
...Do you have any details on the hydraulic motor?

Dave

I am working with AugerTorque. None of the other manufacturers had a smaller unit or wanted to talk about it.

At first I was looking at this unit, ML1100-13

https://www.augertorqueusa.com/product-range/earth-drills/mini-loaders.html

After talking to the sales guy, he put me in touch with an engineer and he pointed me to the ML1600-15 Saying they can do something with the port and gears and get me to about 50 RPM @ 5GPM with no load.

Hydraulic Flow Rate Chart

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