Do I have too big of a pump?

[Billy_PA]

Hello All.

Thank in advance for all you help.

I have upgraded my tractor hydraulic pump from a 8.5 GPM to a 13,5 GPM pump on my 24 HP tractor, I needed the speed.
Now I am starting to wonder if maybe this pump is too large for my tractor. The reason is: When I go to end of stroke with my front end loader the engine RPM decrease more than usual, quite much to be frankly. If running at idle 1000 rpm it will decrease down to only 500 rpm when I go end of cylinder stroke and the PRV kicks in. It stays bogged down even when relieved.

If I'm pushing into a pile of sand with the loader in high rpm (2200 rpm) and try to curl the bucket the PRV kicks in and a lot of whining noise can be heard and I'm not able to curl the bucket with the sand. But If I decrease the RPM to lets say 1000 rpm, I can easily curl the bucket with the same amount of sand I tried in 2200 rpm.

What do you guys think? Do you think my PRV is to small for this amount of flow, or is my pipe dimensions undersized for this flow causing a pipe restriction at higher rpm (flow) which make the PRV open at even the smallest restriction cause by the curl cylinder? Or any other problem I have?

I have not tampered with the relief valves which is set at 2300 PSI according to the books.

Thank you very much for your help!

Bill

 

[Transit]

Bill, I see a couple of problems.

You have increased the GPM volume by almost 60% that means the pressure relief valve must pass 60% more oil.
Relief valves have a maximum flow rate. Indications are that you are exceeding that maximum rate. Changing the valves trip pressure will not change anything.

You bolted on a larger pump. Did you consider the piping losses?
Try to force 60% more oil through lines designed for 8.5 GPM and the oil will get extremely hot. Try sucking that much hot oil from the sump and you risk cavitation damage in the pump.


Why all the speed, most FEL cycle under 20 seconds?

 

[Soundguy]

I agree.. if the hoses , especially the suction hose are undersized.. there could also be cavitation problems..

I hope there are 1/2" hoses on this thing.. also.. check the flow rating for the SCV involved. chances are if it has 1/2" or 3/4" ports it's ok. if it uses a retorn / relief port.. that would also need to be at least as big as the suction line, and no smaller than 1/2".. IMHO

soundguy

 

[Billy_PA]

Bill, I see a couple of problems.

You have increased the GPM volume by almost 60% that means the pressure relief valve must pass 60% more oil.
Relief valves have a maximum flow rate. Indications are that you are exceeding that maximum rate. Changing the valves trip pressure will not change anything.

You bolted on a larger pump. Did you consider the piping losses?
Try to force 60% more oil through lines designed for 8.5 GPM and the oil will get extremely hot. Try sucking that much hot oil from the sump and you risk cavitation damage in the pump.


Why all the speed, most FEL cycle under 20 seconds?

The high flow is not for the FEL actually. My neighbor has a double cylinder dump trailer from the earlier years that I will probably buy from him. With huge cylinders. He got a 10 GPM flow on his tractor and the cylinder movement is still kind of slow. This is the main reason.
I must admit I did have a concern that the lines to not match up with the flow. But just that it gonna generate more heat. Do you know where to get any good info on line size with flow.

Do you think If i found a pressure relief valve which is designed for more flow could help my problem? Like this http://www.princehyd.com/Portals/0/products/valves/catalog/valvesRd1809.pdf

I agree.. if the hoses , especially the suction hose are undersized.. there could also be cavitation problems..

I hope there are 1/2" hoses on this thing.. also.. check the flow rating for the SCV involved. chances are if it has 1/2" or 3/4" ports it's ok. if it uses a retorn / relief port.. that would also need to be at least as big as the suction line, and no smaller than 1/2".. IMHO

soundguy

Thank you for your post.

Do you mean the pressure lines should also be 1/2"? I'm sorry, what is SCV?

 

[Soundguy]

many loader valves have relief built in.. don't know about yours.

scv is your loder valve...

yep.. 1/2" hoses is what I would use for that flow..

soundguy

 

[Farmerford]

Bill:

I suspect the larger pump volume, at 2200 rpm, has increased the velocity of fluid flow in the fittings and/or lines so much that the flow has changed from laminar flow to turbulent flow. I don't have time to make the calculations, but the formula for determining the Reynolds number for your lines should be available on line. The Reynolds number is the fundamental indicator of whether the flow is laminar, transitional, or turbulent. When the flow speeds up enough to transition from laminar flow to turbulent flow, the pressure losses increase several times because the fluid no longer flows smoothly through the lines and fittings, but rather flows in a confused, turbulent manner, which greatly increases the losses. As a practical matter this means the resistance to the flow in the lines and fittings increases greatly, so much so that the combination of flow losses and the load on the cylinder easily reach the pressure relief valve set point.

But when you reduce the pump output by reducing the engine rpm to 1000, as you mention, the slower flow shifts from turbulent to laminar, the pressure losses in the lines and fittings decreases substantially, and a much greater percentage of the pump pressure is utilized in the cylinder.

You aren't hurting anything but you are expending a lot of fuel heating the hydraulic fluid. If you use the loader a lot you might heat hydraulic fluid beyond the design temperature.

As a historical note, the WWII fighter P51 Mustang was one of the first aircraft to use a so called "laminar flow wing" which was designed to greatly reduce the turbulent flow of the customary wing profile and thereby substantially reduce the drag and increase the speed.

 

[J_J]

I think the answer is that it will take all of the 24 HP to run that pump at 2500 psi. You are running out of HP with that large a pump.

The above data is for a 2500 psi pump. If the pump is a 3000 psi pump, then it will take about 28 HP to run it at max. If you back off the rpm, that will relieve some of the HP requirement, and the GPM's will decrease.

 

[AKKAMAAN]

If PRV can't "swallow" all relieved flow at set pressure.....pressure will increase above setting till entire flow is by passed.... I suggest you setup a pressure gauge, 0-5000psi, and check the PRV setting at low rpm, and then throttle to see what happens with pressure.....

If pressure increases when throttle, it would be possible to add an external larger PRV between pump and CV.....but this will not cure your entire problem.....your current CV is most likely undersized too....so even if a larger PRV is added, you will suffer from pressure drop and heating problems from the current CV

Adding a larger pump like this require consulting with manufacturer rep, so all involved factors can be considered.....

Another comment is that 1/2" hoses will make fluid velocity go close to 30 ft/sec which is way over max recommended 25 ft/sec.....so that means you will add extra pressure from undersized hoses too....You will need at least 5/8" size for pressure lines

13.5 GPM at 3000PSI makes 23.6HP.....thats really to push the limits.....
At what RPM is pump rated 13.5GPM??
And at what RPM is engine rated 24HP??

 

[Ford tractor]

As a historical note, the WWII fighter P51 Mustang was one of the first aircraft to use a so called "laminar flow wing" which was designed to greatly reduce the turbulent flow of the customary wing profile and thereby substantially reduce the drag and increase the speed.

I thought the British Spitfire was first.
yes?

 

[Transit]

This should set you off in the right direction;
I think a graphical solution for you will be easer to handle than deep math.
Also keep in mind that all diameters are ID, inside diameters.
You must also consider that the hose end hardware will reduce the ID about 1/8 inch.
Where ever possible eliminate conversions, use direct lines.
http://kuriyama.thomasnet.com/Asset/H SizingNomogram.pdf
http://www.ptospecialties.com/images/nomograph.pdf