Load sensing hydraulics

Reggie.

Does anyone know the explanation of load sensing hydraulics.

Asked a few mechanics and they found it hard to explain it in layman's terms.

Can't find the article "load sensing for dummies" online unfortunately

I know it's used in the likes of a fusion and it's mainly ran by an ecu I think

TheFarrier

https://youtu.be/PbXB2VnhpXw

Hope this helps.

TheFarrier

TheFarrier wrote: »

https://youtu.be/PbXB2VnhpXw

Hope this helps.

https://www.machinerylubrication.com/Read/859/load-sensing-control

A bit over my head but I got the basic idea if it from that video and this article

Reggie.

TheFarrier wrote: »

https://youtu.be/PbXB2VnhpXw

Hope this helps.

Ah nice one. Helps s good bit alright. Never thought of YouTube.

It seems to be better than your normal hydraulics then as it only produces what's needed. Less stress on the system

patsy_mccabe

I worked with these type of industrial hydraulics circuits for years. The best way to understand them is to look at the pump itself.

In old hydraulic circuits like on old tractor, there is a hydraulic gear pump. This has a fixed displacement and so pumps the same amount per turn of the pump regardless of the pumping pressure. If you want to pump quicker, you just rev up the tractor more. These pumps are protected by a pressure relief valve that dumps back to the sump of the tractor. Even when you are not using the hydraulics, the pump is constantly working but dumping back to sump with no pressure in the lines.

The newer type of pumps have a variable displacement and so can vary the amount they pump. They consist of a number of pistons working against a swash plate. When you vary the angle of the swash plate, the amount pumped varies. You can even dead-head these. By that I mean you can set the pump to a high pressure and not have any oil being pumped. Basically pressure on demand. I've seen pumps dead-head at 300bar. The real beauty of these pumps is effeciency, no energy is wasted. They are however more expensive and more completed.
The correct term is Variable Displacement Pump. Here is an animation showing how it works;
https://www.youtube.com/watch?v=c7Rl6e3kkw8

The Nutty M

Patsy covers everything very well. His description is about as easy as it gets,if you can understand how the swash plate is able to stroke the pump then you have it sorted.

You mentioned the fusion Reggie. The fusion is ran best with load sensing to stop the oil boiling in the back end of a tractor with a fixed output pump.
This is a rough simplistic explanation. Let's say the landini has a 110l/m fixed displacement hydraulic pump,that 110 litres is being pumped in the circuit through the servo block in the fusion and back to tank. You want to lift the reel which might take 10l/m,there's still 100l/m of unused oil being pumped through the servos for no reason.
Fast forward to using load sensing on the fusion. That same function of lifting the reel requires the same 10litres but this time you have a variable displacement pump in your dini being stroked by the load sense pipe (3/8 inch hydraulic pipe usually) from the fusion. Pump is stroked to 11% of its output. No excessive unused oil flow and a greater ability to maintain the oil at cooler temperatures in the backend. The fusions usually require 50+ LPM above 170 bar pressure to get good output from them.

patsy_mccabe

Ya, exactly. You never want to pump oil across a relief valve except in an emergency. The pressure drop across the valve is wasted energy and this energy manifests itself as heat in the oil.
I've seen old industrial hydraulic machines and they used relief valve to control pressure. Even if the machine was sitting idle, the oil would be getting hot. The machine would then use more cooling water to keep the oil cool. Even more wasted energy again. Over a year it adds to up a lot of wasted electricity.

Reggie.

The Nutty M wrote: »

Patsy covers everything very well. His description is about as easy as it gets,if you can understand how the swash plate is able to stroke the pump then you have it sorted.

You mentioned the fusion Reggie. The fusion is ran best with load sensing to stop the oil boiling in the back end of a tractor with a fixed output pump.
This is a rough simplistic explanation. Let's say the landini has a 110l/m fixed displacement hydraulic pump,that 110 litres is being pumped in the circuit through the servo block in the fusion and back to tank. You want to lift the reel which might take 10l/m,there's still 100l/m of unused oil being pumped through the servos for no reason.
Fast forward to using load sensing on the fusion. That same function of lifting the reel requires the same 10litres but this time you have a variable displacement pump in your dini being stroked by the load sense pipe (3/8 inch hydraulic pipe usually) from the fusion. Pump is stroked to 11% of its output. No excessive unused oil flow and a greater ability to maintain the oil at cooler temperatures in the backend. The fusions usually require 50+ LPM above 170 bar pressure to get good output from them.

And now that I have your attention. Tell me about closed circuit pumps as opposed to open circuit pumps

The Nutty M

Reggie. wrote: »

And now that I have your attention. Tell me about closed circuit pumps as opposed to open circuit pumps

Patsys first post describes the systems perfectly in way simpler terms than I can.


Open centre is exactly like he says, fixed displacement pump that dumps unused oil back to tank.

Closed centre is a variable displacement pump that destrokes according to the required flow rate. There is no unused oil to send back to tank in this system as fow rate is choked,but pressure maintained by the destroking of the pump. (We'll leave case drain out of this for simplistic terms)

Load sensing is a closed centre system with a variable displacement pump. But where it is different is both flow rate and pressure are regulated by the destroking of the pump with the use of a compensator circuit.


Destroking the pump is the key to variable displacement pumps so if you get you head around that you're laughing. Every system after that then uses various forms of destroking from pilot pressure relief valves to seperate small charge pumps maintaining pressure.

visatorro

Handy way of thinking of load sensing I found was a hydrostatic telehandler or fork lift. It's a pump the sends oil to the drive motor. Nothing happens until you touch the pedal, the more you put your foot down, the more oil leaves the pump. The faster your machine moves.

Can get very complicated with different valves and circuits. Also different manufacturers will have different names on what more or less is the same thing.