Large Property Cleaning

Discussion in 'Heavy Equipment & Pavement' started by AWJ Services, Oct 13, 2013.

  1. AWJ Services

    AWJ Services LawnSite Platinum Member
    from Ga
    Posts: 4,276

    The Ex you have will not make 19gpm at 3000 rpm. The 19 gpm will be at a much lower pressure. Your engine makes 42 hp. Assume min 80% loss efficiency from pumps and that leaves 33 max available too the whole machine ao unless Bobcat has figured something out nobody else has your machine cannot have 33 hp available at the aux circuit, Your machine will have about 19 hp available real world.
     
  2. YellowDogSVC

    YellowDogSVC LawnSite Gold Member
    from TX
    Posts: 3,752

    specs say 19 at auxiliary at 3000 psi. 26 gpm on the rest of the system. My Bobcat is only 85 hp but puts out 37 gpm at 3500 psi confirmed on flow meter. My mulcher is rated for between 35 and 40 gpm and it's performance is spot on for what it should be. The skids specs are roughly double what the ex specs are and it also has power to move and lift a 2650 lb attachment without much rpm loss to my cutter. Somehow it works.
     
  3. AWJ Services

    AWJ Services LawnSite Platinum Member
    from Ga
    Posts: 4,276

    Specs actually say 19 gpm and then it says pressure 3000 psi. It does not say 19gpm at 3000 psi.

    I will add that if your skid makes that then it is a stellar performer. What type of flow meter did they use to test it ?
     
  4. YellowDogSVC

    YellowDogSVC LawnSite Gold Member
    from TX
    Posts: 3,752

    I'm not sure of the flow meter... same one they've always used. it was big and heavy. When I had my pressure gauges hooked up to my mulchers, I can see the pressure drop after awhile. When it comes up against a load, the pressure will spike up and down but it does hit over 3k at full rpm.
    My CAT did the same thing and when it had a problem with relief valve kicking in too early (or some type of bypass which was resolved by a software update), the pressure would drop dramatically even though the gpm stayed up. Been awhile since i went through all that but the pressure spikes are seen, in my case, when resistance is met.

    I disconnected my pressure gauge because it always leaked but would like to hook it back up and see if I'm remembering correctly. Getting old, you know.

    As far as being a stellar performer, what I do know is that my Bobcat are more consistent in keeping different mulcher rotors up with my gear pump than the CAT did with it's piston pump. I'm not sure why that is but I've not been disappointed in performance considering I'm running a skid steer mulcher. It powers through the thickest shreds mixed with 10-12" logs and I don't overheat at all but I still can't use it like a bulldozer. I use finesse to make up for lack of horsepower but it works for me.

    Just thought of this. If my pressure was dropping off significantly and/or my gpm was dropping off, then I'd see ta reduction in rotor speed head and more stalling with the skid.

    On the specs for the mini- it's system relief at at auxiliary is 3045 and it says 19 gpm.

    The system is capable of more pressure, however, because other cylinder circuits like angle blade, and slew have 4k plus psi.

    I"m not sure why the machine makes 26 gpm for everything but auxiliary and has different pressures for different circuits?
    Gives me a headache.. and I'd like to figure it out before I get a nice toy like you did for mowing.
     
    Last edited: Nov 9, 2013
  5. AWJ Services

    AWJ Services LawnSite Platinum Member
    from Ga
    Posts: 4,276

    I have spent the last month trying too decipher mini ex flow myself. My Kubota is rated the same as you Bobcat so i feel pretty comfortable with what I am saying. One thing you always defer back too is performance. Regardless of specs rotor speed and recovering are the best test for actual flow. You can always look at the size of the hyd motor on your mulcher( displacment) and take the rotor rpm and back figure your actual flow.
     
  6. Digdeep

    Digdeep LawnSite Bronze Member
    Posts: 1,840

    YellowDogSVC...I'm going to have to disagree that you'll actually see a legitimate 37gpm@3500psi on a reputable flow meter. I've done this test on a T870 with a friend of mine who is a current Bobcat salesman and his lead mechanic in his Bobcat shop. We were getting less than 12hyd hp at 3500 psi and less than 22gpm at all pressures above 3000psi. As a matter of fact, we did not see 37gpm once we got above 2100psi. Max hyd performance was around the 2500-2700psi range and the pump was producing around 31-35gpm if I remember correctly. In no scenario will you see 37gpm going through a flow meter @ 3500psi in your 85hp machine.
     
  7. YellowDogSVC

    YellowDogSVC LawnSite Gold Member
    from TX
    Posts: 3,752

    can only report what I saw. I've been running high flow attachments since 863 machines came out and have watched the flow meters so I could see if my machine was in spec. I'm not saying with 100% certainty that I saw 37 at 3500 but I saw several of the machines reach the flow (one was putting out more than specs) and my pressures were withing the specified range of 3450-3550 which is what Bobcat calls for. I watched my CAT 272c hit it's max flow and pressure then drop off, too. I don't think the 870 has a different pump and the pressure is supposed to be the same or within the same range. the 330 put out more gpm than it was rated for and had a similar situation with one of my s300k series machines.

    I guess it doesn't matter as long as the job gets done for the attachments you plan to use.
     
  8. AWJ Services

    AWJ Services LawnSite Platinum Member
    from Ga
    Posts: 4,276

    It really frustrates me that the OEM specs there machines the way they do. In my opinion it is mis leading and confusing.
     
  9. YellowDogSVC

    YellowDogSVC LawnSite Gold Member
    from TX
    Posts: 3,752

    I agree that the specs are confusing but I have also seen several machines out of spec both above and below.

    I imagine pressures average about 2500 because I've watched the spikes up and down but I don't see how gpms drop on a gear pump at full rpm and I have also seen the pressure spikes when I get into something difficult. Just never paid much attention to it as long as it was doing what I thought needed to be done. When it didn't "feel right" or I thought performance was lacking, I had it checked or turned up. Never asked to have it turned down when it was beyond specs. :)
     
  10. AWJ Services

    AWJ Services LawnSite Platinum Member
    from Ga
    Posts: 4,276

    I will add one thing that GPM and pressure together determine actual amount of power to the attachment. Pumps will always lose flow as pressure is increased. Does not matter what type of pump it is. The pump actually is graphed and it is often refered too as a pump curve. Flow will be high at low pressure and low at high pressure.
     

Share This Page