curing bucket flop

ericm979 · Dec 9, 2017

I needed more to understand the counterbalance valve and I found this chapter from a textbook: BOOK 2, CHAPTER 5: Counterbalance Valve Circuits | Hydraulics & Pneumatics

Sounds like the simple one way restrictor I'll be using is sub optimal, in that it's tuning will depend not only on the bucket load (which I knew about) but also the pump output (engine speed). Well it's cheap and easy to install anyhow. I wonder if it'll eliminate or slow the fast dump feature when set for normal dump?

oldnslo · Dec 9, 2017

ericm979 said:
Sounds like the simple one way restrictor I'll be using is sub optimal, in that it's tuning will depend not only on the bucket load (which I knew about) but also the pump output (engine speed). Well it's cheap and easy to install anyhow. I wonder if it'll eliminate or slow the fast dump feature when set for normal dump?

Presuming that your Fast dump is a regenerative dump then yes the flow control could slow the dump down depending on how it is set.

A counterbalance valve would also prevent the regenerative system from working.

Nice find on c'balance circuits explanation.

ericm979 · Dec 28, 2017

I got the flow control valve installed. It does slow the fast dump. I'll be running the engine at a consistent RPM (2000) to keep changes in pump output from being a factor. Also with the added weight of the grapple vs the bucket, and the cylinders to operate it, I want a faster pump speed. At times I have run the RPMs lower when using the bucket, especially when I have a ground helper and want to be polite.

I found a setting (about halfway in) that gets rid of most of the bucket flop but doesn't make the dump much slower. I have only tried it with the grapple so far. The valve's close enough to the operator's station that I can reach it if I stand and lean over, so it's pretty easy to adjust. It's the upper most line on the loader so it's right there on the loader arm.

The biggest problem with this has been getting one of the NPT to JIC adaptors in the valve to seal.

patrick_g · Dec 28, 2017

Just what is bucket flop?

I have been using my Kubota FEL for 15 years and never experienced what I think is being discussed. I do have a knob on a valve under the front edge of my seat which control the hydraulic flow so you can slow it down a bit to not be so fast/herky jerky if you want.

Patrick

Peter 315 · Dec 28, 2017

That knob at the edge of seat is for the 3 point hitch

ericm979 · Dec 28, 2017

Raise the loader and dump the bucket. When it gets near the bottom it flops back and forth a little like it's loose. The faster you dump it the more noticeable it is (possibly because of momentum). It's more noticeable with a heavier implement like a grapple than it is with a bucket. My Kubota B7100 didn't do it (though I only ever used the bucket on that, and it was a light bucket). LS tractor owners have also complained about the problem.

I think the cause is cavitation in piston end of the cylinders as you dump. The weight of the bucket/grapple pulls the pistons out faster than the fluid can replace it, creating low pressure. Adding a restriction in the output direction on the rod end is a band-aid (see oldnslow's posts above). I don't completely understand why some loaders do it and others don't but I suspect that Kubota just specs better loader valves.

oldnslo · Dec 28, 2017

ericm979,
The reason Kubota BX & possibly's B's don't have the problem with bucket flop is that Kubota uses a valve with regenerative dump. Regernerative dump connects both ends of the cylinder to pressure which help prevent the over running condition that causes cavitation.

Yes better valves that are designed to meter out from the rod end will also help reduce this problem.