Hi,
What exactly is the difference between a load sensing system and a constant flow system. For example, I was reading an artical on the following website,

http://www.insidersecretstohydraulics.com/hydraulic-load-sensing.html

They had stated an example of the winch to demonstrate a load sensing system. What difference would it have made, if for that particular case a constant flow system had been used?

Mechboy,

Load sensing systems are energy efficient (saves energy) as compared to systems with constant displacement pumps.

For that particular case, if constant displacement pump is used then pump power (in HP) = flow,lpm X Pressure, psi / 1714, which is constant throughout usage.

For load sensing systems, pump displacment (flow) is adjusted based on load induced pressure, pump power (in HP)would be economised.

Directional control valves used are different for load sensing & constant displacment pumps.

AKB

Lets make a math example.
Both system have a stand-by pressure for the pump lets say 300psi, load pressure is 1500psi,
constant high pressure is 3000psi.

Load sense system will make pump do 300+1500psi=1800 psi. Delta p over directional valve is 1800-1500=300psi times flow rate, which will be the power lost as heat over directional valve

Constant pressure system will make pump do 3000psi. Delta p over directional valve is 3000-1500=1500psi times flow rate will be the power lost as heat over directional valve.

In this example constant pressure system loose 5 times more nergy than load sense system. Difference will increase on low pressure loads and decrease on higher pressure loads.
Make sense?

Have a look at Eaton File at
www.bostonweatherhead.com/products/pdfs/03-206.pdf

Are those ANSI symbols Brendon Casey is using?

i always try to discuss/explain my "little" hydraulics knowledge in a very basic way
unless otherwise a computaion is needed to solve a problem.

my answer to this question is also a little very simple , and i hope you research and read the book so you can correct me if i missed some. ... about variable displacement pump controls. there are a lot of them!!! i suggest REXROTH ( Im a big fan of rexroth and i hope they pay me for promoting it ).

but honestly im very rusty in hydraulics nowadays... In a constant flow system as you may call it, the variation of flow is achieved if you reached the setting of the flow/pressure compensator... the pump swashplate or cam ring(for vane pumps) will be pushed by an actuating piston thereby changing the flow( remember that it has to reach a pre adjusted setting!)

for load sensing, the explanations is almost simmilar to the term itself! the variation of flow is dependent always on the pressure sensed from the load!!! hehehehe a load sensing line is connected from the load to the load sensing port of the pump. therefore just whatever is needed to operate the load is what is being given to it. they dont need to reach a certain preset pressure to vary the flow of the pump. most of the pumps in load sensing mode has a destroke pressure of more or less around 20 bars. most valves used in this application are float type, meaning blocking the "P" line and "A" & "B" are connected to tank. shuttle valves are used in the circuit too.