Possible hydraulics issue

[woodlandfarms]

I dunno. I have this feeling my pto circuit is not running up to snuff. It may be all in my head but I don't remember bogging down mo mower in tall grass but this season I seem to be doing a lot of backing up to get the mower back to speed.

An thoughts on testing the issue?

 

[SpringHollow]

Hi Carl,

Do you have a pressure gauge to Tee into the circuit to see what the pressure is when it bogs down?

Ken

 

[J_J]

Like Ken said.

Install the gage for monitoring and trouble shooting.

Notice the pressure when it is cutting good.

Notice the pressure when it stalls.

Could be worn blades, pump not performing well, mower deck hyd motor bypassing due to wear.

Check relief valve for correct pressure.

Do you think the blade speed is OK?

Did you switch to heavier blades?

 

[MossRoad]

First thing to check is sharpen the blades. On my brush hog, the blades become blunt instruments of destruction quit often in heavy brush. In thick grass, they will bog down a lot more than in woody brush. Sharpening them makes a noticable difference.

Then check your hydraulics.

 

[ponytug]

I can second this. I was just out mowing, and ended up thrashing and clumping, and then I remembered that I hadn't sharpened the blades. It makes a big difference.

All the best,

Peter

First thing to check is sharpen the blades. On my brush hog, the blades become blunt instruments of destruction quit often in heavy brush. In thick grass, they will bog down a lot more than in woody brush. Sharpening them makes a noticable difference.

Then check your hydraulics.

 

[cqaigy2]

Also the grass is pretty wet and that makes it a little tougher to get thru.

 

[woodlandfarms]

So I will answer questions and ask some more

No, I do not sharpen my blades. The mower is a 90" rough cut mower which I have added thicker / heavier blades to. I have never sharpened my blades. Issue for me is that I mow roughly 22 acres of land that has limbs and rocks and what not and having a sharpened blade seems to be futile. Plus I understood it as you never really sharpened brush cutters as you wanted the brush to splinter so it would not grow back. Me being a bit of a novice at all of this could be making a wrong decision.

But, OK, sharpening noted.

so to pressure monitoring. Yes, I have a gauge but it was set up for a different circuit. Does anyone have pix of there monitoring system? I do have a permanent gauge but it is on my brake line, I guess it is watching the tram pump.

So, for my Hydraulics theory. Pressure would be more important than flow in regards to this issue. (?) I get the two of them mixed up a bit.

So where would I put the gauge in the circuit? meaning before the mower motor or after? What am I looking for? Assume my PTO circuit is 3000PSI, what should I be seeing and what would be wrong?

I am going to assume 3000PSI would not be seen when mower is operating until it bypasses (I assume it bypasses when it bogs down). I know the PTO has a bypass on its valve as well.

Thanks guys as always.

 

[J_J]

Carl, if you install a tee and 1/4 in male QD into each hyd circuit, you can plug the gage with female QD in whatever circuit you want to read.

As far as hyd pressure, the gage will read whatever the load on the hyd pump. The pressure will vary as you cut, easy to difficult, to relief pressure at the stall point.

However, if the hyd system never relieves, then the low pressure could be in the hyd pump, hyd motor, or valve.

If the hyd circuit is set to relieve at 3000 psi, and you see 3000 psi on the gage, then you can assume the pump and hyd motor is working as advertised.

 

[woodlandfarms]

Thanks JJ. I guess I misunderstand on the rig you are talking about. My QD on the PTO circuite are 1/2 or 3/4. 18GPM. The rig I build is a dead head so will work out a T connector system.

 

[ponytug]

Dear Carl,

Just a small preamble about power transfer with hydraulic circuits: power is the product of flow and pressure. In an ideal hydraulic system,

• High flow and low pressure difference = low work (power).
• High flow and high pressure = high work.
• No flow and high pressure = no work being done.

There are lots of hydraulic calculators on the web that let you interactively explore the tradeoff in exact detail, but remember that this assumes no wear or losses in your pumps/motor (which may be an issue).

If you consider the hydraulic circuit for the PTO, the PTO pump is sucking oil out of the reservoir at a little less than atmospheric pressure. As the PTO pump is moving oil, pressure is generated by the resistance of the hoses and valves to the flow of the oil, as well as the energy losses in the moving oil(wasted work), and by the brush cutter motor (useful work). There is also some oil that leaks past the PTO pump, and some oil that leaks past the brush cutter motor, both leading to reduced power transfer (more wasted work). If there is little or no work being done by the brush cutter, the pressure between the PTO pump and the motor will be low. If you measure the pressure between the PTO pump and brush cutter mower when the brush cutter stalls, it should be at 3000psi, or whatever your PTO relief is set at. This is an important point- the pressure in the PTO circuit will be low when there is little work being done. As the workload increases, the pressure will rise. In an ideal world, when the pump is running at full speed, it will be able to generate something like 3000psi at 15gpm to transfer all of that power to the brush cutter. The fact that this heats the oil in the tank pretty rapidly tells you about the energy wastes in the system.

To the extent that your PTO relief doesn't kick in and you don't reach 3000psi at a stalled motor, you may have inefficiencies or wear in the either the pump/motor. Some hydraulic motors have built in bypass circuits for stalls. I don't know what your brush cutter design is. To the extent that your oil is thinner than the motor/pump specification, you may have more leakage, lower maximum pressure, and reduced power transfer.

Does this help?

Finally, if you plan on leaving the pressure gauge in the circuit, you may want to consider putting a snubber on the gauge side of the "tee" to reduce the pressure shocks that are normal in the PTO circuit.

All the best,

Peter