May have a possible answer on the 7520 slow loader problem.

CuzPat62 · Nov 1, 2006

Hello to All,
I was reading in my loader manual today and found some interesting spec's. On page 14 it lists all the loader specifications. In Mahindra's literature/brochure on the 7520 and on the web-site under the ML 275 loader spec's this is what is advertised:

Cycle Time Spec's

*Raise Boom - 6.2 seconds
*Lower Boom - 4.1 seconds
*Dump attachment - 3.2 seconds
*Retract (rollback) attachment - 2.5 seconds

Nothing is mentioned about what rpm's the tractor is turning in relation to these spec's.

Now, here is what is in my manual:

*Raise Boom - 9.0 sec @ 1500 rpm, 7.6 sec @ 2000 rpm, 6.2 sec @ full rpm
*Lower Boom - 5.7 sec @ 1500 rpm, 4.9 sec @ 2000 rpm, 4.1 sec @ full rpm
*Dump attachment - 3.6 sec @ 1500 rpm, 3.4 sec @ 2000 rpm, 3.2 sec @ full rpm
*Retract (rollback) attachment - 4.0 sec @ 1500 rpm, 3.0 sec @ 2000 rpm, 2.5 sec @ full rpm

The faster spec's that is advertised by Mahindra is achieved when the tractor is being operated at full rpm's or otherwise full throttle. The spec's are considerably lower (or slower) when the tractor is operated at more normal operating rpm's. So, if you were to do a timing test on the functions of your loader; to achieve the spec's advertised by Mahindra you would have to operate your tractor at the full rpm's. If you looked at the faster timed spec's advertised by Mahindra on the ML 275 loader and compared it to the speed of your loader operations at normal rpm ranges, then of course it will appear to be slow. How many of you operate your tractor at full rpm's? My take is that I believe the advertising could be a little misleading due to the fact of not mentioning the rpm's in relation to the advertised spec's. So, what we are thinking about our loader operations being slow might be normal if we run our tractors at the more normal rpm ranges.

Now, what about my theory on the slow loader problem? Could I be on track here? I may be totally off base here with this whole idea. Not bashing Mahindra at all, I really like my tractor. I'm just looking for an answer on the slow loader problem that myself and others have brought up due to experiencing it. Just thought I might be on to something here.

Comments?

Fredex · Nov 2, 2006

Seems easy to check out - 5 minutes or less with a watch with sweep second hand of digital w/ seconds readout. Better yet, a cheap stop watch.

cwray57 · Nov 2, 2006

CuzPat,

I would say that you are more than on the right track, you are absolutely correct! The speed of the hydraulics is relative to hydraulic pump flow, which is directly related to engine RPM. I work for a heavy equipment manufacturer and "all of our travel speeds and hydraulic function times are understood to be at rated engine speed" unless otherwise stated. I believe this an industry standard.

Clark

Slippy · Nov 2, 2006

Would be easy to check. But...my question would remain as to why the slow speeds at the typical operating rpms. I am also now wondering how that will effect the operation of a bh. With my 6000 and 511bh I can get a lot done at about 1500 rpm, and hoe responds well. Does this mean that on a 7520 I would have to max out the rpms to get the same or similar response? Not something I can just run down to the dealer and check.

MtnViewRanch · Nov 2, 2006

Slippy, I do not have a back hoe for my 7520, but I have found that I normally operate at about 1750 rpm without ear protection and about 2200 rpm with ear protection.

Now with my Case 580E backhoe, I will dig at 1600 rpm until I get a rhythm going and then bump the rpm's up to about 2000. Each tractor is a little different, but not anything that you couldn't get used to very easily I would think.

SPYDERLK · Nov 2, 2006

CuzPat62, As you say the rpm will affect the speed of any hydraulics. Typically hydraulic speed will double with doubling RPM since pumps in most tractors are positive fixed displacement. If a restriction in the circuit resists higher flow to the point that a relief valve comes into play then some of the pumped fluid would be wasted and the implement on that circuit would no longer increase speed as rpm rose.

The main issue with the 7520 / 275FEL is that the loader never can be made to move fast enuf to show that 17GPM is being delivered to it. Even using the quoted max speed the delivery rate calculates out to around 13GPM. My 7520 will not lift in less than 7 seconds at 2500 RPM. This equates to 12GPM tops. The 17 GPM hydraulic delivery spec quoted by Mahindra is in question. The loader would definitely not be slow if it was getting that delivery.
Slippy, The BH only has one cylinder for each function and even tho they are bigger they still dont need as fast a delivery to give good speed. I have no problem with BH speed at 1500RPM. When I get better at it I may go up to 1750. The thing is - - the BH should be a lot more lively on the 7520 than on the 6000 considering the hydraulic spec. I wonder if it is.
Larry

Blu 82 · Nov 3, 2006

All--I went to the website for the Bradco BH and it says "optimum performance with 9-12 GPM hydraulic systems". Maybe 17 GPM won't make it perform better?? Could that be the same w/the FEL since it also fits the 6520 that only has 11.4 GPM?? Of course the raise/lower/dump/retract times are different for the 6520 and the 7520 (more hyd flow). Could there be something in the hyd system of these 2 attachments that won't allow them to take full advantage of the 17 GPM??

Has anyone timed the FEL to see if w/in spec stated in the Mahindra advertisement (6.2 sec to raise; 4.1 sec to lower; 3.2 to dump; 2.5 to retract)? Also, ad does list 2500 rpm as the rpm for the specs.

BobG_in_VA · Nov 3, 2006

Blu 82 said:
All--Has anyone timed the FEL to see if w/in spec stated in the Mahindra advertisement (6.2 sec to raise; 4.1 sec to lower; 3.2 to dump; 2.5 to retract)? Also, ad does list 2500 rpm as the rpm for the specs.

Blu: Suggest you trot on down to your local Mahindra dealer (who has a 7520 on the lot), have him/her do the test and report back to us your findings. Thanks BobG in VA

SPYDERLK · Nov 3, 2006

Blu 82 said:
All--I went to the website for the Bradco BH and it says "optimum performance with 9-12 GPM hydraulic systems". Maybe 17 GPM won't make it perform better?? Could that be the same w/the FEL since it also fits the 6520 that only has 11.4 GPM?? Of course the raise/lower/dump/retract times are different for the 6520 and the 7520 (more hyd flow). Could there be something in the hyd system of these 2 attachments that won't allow them to take full advantage of the 17 GPM??

Has anyone timed the FEL to see if w/in spec stated in the Mahindra advertisement (6.2 sec to raise; 4.1 sec to lower; 3.2 to dump; 2.5 to retract)? Also, ad does list 2500 rpm as the rpm for the specs.

Do you mean "Has anyone else?" Pls see post just before yours.

However, yes the loader could be limited in speed by the 3/8 Hyd lines routed thru the boom to feed the manifold block on the loader. A 6' long 3/8" line would give significant backpressure to a 17GPM source. I wouldnt think it would take 2500# to push that amt of flow thru tho.
Larry

MadReferee · Nov 3, 2006

SPYDERLK said:
the loader could be limited in speed by the 3/8 Hyd lines routed thru the boom to feed the manifold block on the loader. A 6' long 3/8" line would give significant backpressure to a 17GPM source.

A 3/8" ID hose is a little too small for a constant 17 gpm flow.

Hydraulic Reference Chart