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

 

[mmurphy]

Another thing to add in. Is the valves rated for GPM on the old pump, and running short with the new pump?

 

[Billy_PA]

Gentlemen.

Thank you very much for all of your replys. Very very much appricated. I will try to answer everyone in this single post.

J_J: It does not feel like I dont have enough HP to run this pump, it wont stall the engine, it bogges down in RPM but never stall. But maybe it should not even bogg down?

Farmerford: sounds like a very good root cause for my problem. As many other also have mentioned I should go trough my lines for restriction (size)

AKKAMAN:

Thank you for the advice on the gauge. Where should I install this?

Do you think If I installed a PRV which is specified for the flow and having the tractor pressure lines change too a larger cross would help me? The FEL lines are hard pipes mainly, not so easy to change these. Or do you think this would be a waste of money and time?
The flow is rated at 2500 rpm. My HP is rated at 2300 rpm.


Transit: Great documents, thank you!

 

[Billy_PA]

By the way,

If I change the PRV to a larger type. How should it be set against the FEL prv? Which should kick in first?

 

[AKKAMAAN]

By the way,

If I change the PRV to a larger type. How should it be set against the FEL prv? Which should kick in first?

You add it because you want it to kick in huh??? Set the new prv valve slightly lower than the FEL prv....if the FEL prv valve "kicks in", then the new prv is either undersized or not set low enough (or FEL prv high enough) keep 100-200psi pressure setting between the two prv's

Gauge need to be plumbed in between pump and first next valve....

I still think this pump change is a BAD move.....as stated earlier....you are trying to extract more hydraulic power than engine can provide....and lowering rpm's sure do lower flow, but it also lower the engine power....so thats not the solution on your problems either.....but to try to do the best out if the mess.....make my suggested pressure test...that should tell some about the future of this....

I think changing pump size this drastically is like adding a ticking bomb.....out of control....YOU BETTER BE SAFE DOING ALL THIS THINGS!!!

 

[J_J]

One side note to consider, is that you may be using the tractor for a couple of hours, and occasionally you may cause the pressure to build up to the max. As you probably know, the pressure only builds against the load you put on the system. Just raising the FEL arms only requires a couple of hundred lbs. About the only time you see max pressure is when lifting a full bucket at max weight, and then only briefly, and when at the end of cyl travel. If you could ever run a paper graph on the hyd pressure, I think you would be surprised as to the amount of pressure used at different times. However, you can install a gage in the system and monitor the pressure. When you hear the relief valves whining, you know you are up to the relief pressure. You probably have noticed that things on your tractor work much faster now due to the increased volume of fluid. Even if you reduce the rpm's to reduce the flow, you also reduce the HP. I don't see you having trouble unless the reliefs stay on for extended times. You really did not increase the power of the hyd system by going to a larger pump, unless the pump has a higher pressure rating. If you were to change any lines to match the flow velocity, you would have to change all the pressure lines in that circuit.

 

[J_J]

As far as the rpm decreasing when trying to curl a bucket under load, you have asked the hyd system to run at max pressure, and when the relief valve kicks in, the only path for the fluid to go is out the relief valve, and at the same time, you have asked the engine to produce max HP. At idle and trying to load up a bucket, same thing, when the pressure gets to max, the engine will struggle to maintain rpms. Just use what you have in a logical manner. If you want more force, that would require larger cylinders, and that is only if the front end of the tractor can handle the increased force/load

 

[David Devuono]

Maybe we should know more about this dump trailer? It must be HD with dual dump cylinders. A 24HP tractor probably is in the 2000 pound range. In my area a 17 year old lost his life recently. They determined he was pulling a wagon with 4000 pounds of hay and it overwhelmed his tractor. Hopefully you are in a flat area.

 

[Transit]

Billy, maybe you will have a clearer picture if I explain pump problem I was having with my Jinma254.
I was using the FEL heavily for ground work; I ended up replacing pumps every 50-100 hours. The pump bearings would burnout and the gears would cut into the pump body. The first replacement maybe a bad pump, number 2 another bad pump. Number 3 and 4? Something is fundamentally wrong.
At first I did not find any reasons for the pump failures, and then I noticed that the pump part number in the tractor manual although correct was different from other 254 pumps. The difference was due to the flow rate, the pumps that were failing are rated at 8.5 GPM and the others rated at 3.5 GPM. The up graded pump was for slow response. However, reverse engineering the system reveled major system @%&%$#. All the hydraulic lines were sized for a 3.5 GPM pump and to make matters worse, the tractor uses metric lines and the FEL uses inch lines. What is in-between? Adaptors. Installing a pressure gauge at the pump output showed that there was a constant load of 500-600 psi the pump was working aginst just pushing oil around the system.

Using the Hydraulic Nomographs I replaced all the pressure lines with 1/2 inch ID lines, removed all the adaptors to run direct lines, meaning that one end fitting is inch and one is metric. Replaced the suction, pressure relief valve and sump return with 1 inch ID lines. Now the oil is 30 deg cooler and no more blown pumps.

 

[J_J]

Billy_PA

Here is a velocity chart to help you choose a hose .

http://www.gates.com/downloads/download_common.cfm?file=NomographicChart.pdf&folder=brochure

According to the chart, 1/2 would be OK, but there is a window for any variance.

The diagram also reflects an oil viscosity of about 315 SSU at 100 degrees or 68 CST

 

[Billy_PA]

Gentlemen. You are all very helpful.

Transit: Thank you very must for your story/information Did you also replaced your loader lines? And to a more flow PRV or just the PRV line size ?

J_J: Thank you for your explanation and the chart. My intention with the pump upgrade was to get the increase in speed not the force. According to the dealer the only difference between the pump is the flow out put, pressure rating is the same.

AKKAMAN: Yes the pressure test is next on the to do list of mine.