3-Point Hitch L-series Jerky 3PH - Jeff's homebrew repair.

[Slimson]

Does the flow control valve allow you to select full flow rate if you choose?

There are some applications where I just want the 3pt up and don't need fine adjustment. I would probably leave it selected to full rate unless I needed a smooth adjustment.

This mod alone seems like a great solution without getting into the position control valve- if I want fine adjustment, slow is good.

 

[J252]

The video you posted was at 2000 rpm, and was pretty smooth. How does the flow divider valve work at lower speeds (and pump flow rates), at idle for example? Does it scale the delivery from the CF port to be the same volume (provided the pump still produces that much flow at the lower speed, of course), or is the lift proportionally slower?

Sean

The pressure compensated flow control valve strives to keep the flow constant out of the CF port regardless of changes in inlet flow. It does so by determining the absolute flow out the CF port using the deltaP across an internal orifice. For those interested in the theory behind this valve type see HYDRAULIEKWEB.

Practically I haven't noticed a difference in 3PH speed due to changing RPM. I may try to post a video testing this, though it will be 2 weeks before I'm near the tractor again.

Does the flow control valve allow you to select full flow rate if you choose?

Yes. Actually since I purchased a 0 to 16 GPM valve (due to availability), and our system is ~6.4 GPM, pretty much every setting over 5 (on the arbitrarily marked scale of 1 to 10) gives full flow.

 

[Chilly807]

This is getting interesting.. I looked at the Prince hydraulics catalog today, either the FCV with top connections or side connections should work, I think the one with 3/8 NPT threads might be the best match for the L3400, since all the existing fittings are 3/8 (#6 SAE). This looks like a good project for the winter or spring, we're still pretty busy with the tractor at the moment, and I have enough irons in the fire myself.

Like Slimson said, when I want fine control over the 3 point slower movement is usually a good thing anyway. I like the part where the valve is adjustable, for other jobs like mowing or logging, quick is good, and it's normally in one motion.

Sean

 

[oneillmj]

Jeff, thank you so much for posting your mod. You've potentially saved us thousands of dollars on a new tractor purchase by not having to bump up from an L3700/3800 to a more expensive Grand L model (or another manufacturer) to avoid the defective 3-point hitch problem. Thanks. If anyone tries Jeff's mod on a newer model 3400/3700/3800, please post your results. Thanks again.

Mike

 

[Chilly807]

I'll be trying it, probably over the winter months..

Sean

 

[dilligaf241]

Jeff, Would you give us a detailed list on the other parts to do this? The plumbing parts, hose lengths and such. I'm interested in doing it to mine and would like to order as much as possible at one time. Plus there isn't anyone near me to get most of this stuff from, over an hour drive in any direction, so I need to order by internet if possible and want to make sure I order right the first time. Thanks so much, and thank you for this wonderful solution to something that should have been handled by Kubota in the first year or so of production.

 

[J252]

Jeff, Would you give us a detailed list on the other parts to do this? The plumbing parts, hose lengths and such.

Sure, in a week or so I will be back at the property and should be able to compose a list. Keep in mind, if you select a different flow control valve brand with different (size/location) ports, the hose lengths and the fittings right at the flow control may be different. I used a Princess Auto offshore valve.

 

[Texas Fella]

Very interesting post. The one thing that I would like to see is what kind of back pressure the flow control valve places on the pump itself. By restricting the flow to the 3-point, the pressure on the pump side of the valve must increase some amount. I know that these simple gear pumps can not take very much back pressure before they begin to fail. As a general rule on Kubota tractors, back pressure should be less than 400 psi (down around 300 is much better). Just a thought before everyone starts to add this valve and have massive pump failures down the road.

 

[Chilly807]

Very interesting post. The one thing that I would like to see is what kind of back pressure the flow control valve places on the pump itself. By restricting the flow to the 3-point, the pressure on the pump side of the valve must increase some amount. I know that these simple gear pumps can not take very much back pressure before they begin to fail. As a general rule on Kubota tractors, back pressure should be less than 400 psi (down around 300 is much better). Just a thought before everyone starts to add this valve and have massive pump failures down the road.

Might be worth tying a gauge into the PB circuit to check before and after the install, but I think that's why the valve has the "return to tank" port. Whatever doesn't go to the CF port gets returned to tank at very low pressure.

Sean

 

[J252]

The one thing that I would like to see is what kind of back pressure the flow control valve places on the pump itself. By restricting the flow to the 3-point, the pressure on the pump side of the valve must increase some amount. I know that these simple gear pumps can not take very much back pressure before they begin to fail. As a general rule on Kubota tractors, back pressure should be less than 400 psi (down around 300 is much better). .

By back pressure, I assume you mean the pressure seen at pump due to friction losses when this is no load placed on the system? (ie: occurring when the system is just flowing to tank without any control valve/cylinder being activated.) Other than the unnecessary creation of heat, is there a specific reason why this should be kept to 300-400 psi? Keep in mind, under working load conditions the pump handles pressures up to 2300 psi.

Either way, I don't think there is any problem of increased pressure. The flow control valve primarily diverts the excess volume flow back to tank at low pressure. That said, there is a bit of extra friction loss with the valve in place versus not there. I did check it when I installed, and though I don't remember specific values, I recall it being a small enough difference not to worry me. When I'm back on the property, I'll see what I wrote down for pressure.

but I think that's why the valve has the "return to tank" port. Whatever doesn't go to the CF port gets returned to tank at very low pressure.

Yes.