Reader, Raja, asks:
The LS (load sense) setting is usually stated as 10-30 bar. How do I determine the appropriate pressure for an LS setting between the 10 to 30 bar? I have a problem with a crane, which slows down if two operations are carried out together. It is run by a H1V Sam Hydraulik pump.”
The load sense setting on a variable displacement piston pump dictates the rate of flow the pump will provide through a given set of valves. A load sense signal is normally tapped in somewhere downstream of a flow control, directional valve, counterbalance valve etc, by way of a load sense check valve network.
The load sense compensator will compare pressure at the outlet of the pump with the load sense signal downstream of all the valves to maintain, if possible, the standby pressure setting of the pump (somewhere between 10 and 30 bar in your case). Essentially the load sense function measures pressure drop and tries to maintain standby pressure by increasing or decreasing displacement (and therefore flow). This is a highly efficient method of variable flow capability, which is why so many off highway machines use load sensing pumps.
You didn’t mention if this was a recent problem or has persisted since the machine was new, but there could be a couple reasons you’re experiencing a slow down during simultaneous functions. It’s obvious you’re not getting enough flow to satiate the demand of both functions, but I would first confirm if your pump flow is up to the task based on its maximum capacity. It wouldn’t do any good to play around with settings if you’re simply asking 100 L/min from an 80 L/min pump.
If you know pump flow should be more than enough, you have an easy option. If you do not have enough flow, you have one difficult option. First, I would try increasing the load sense (standby) setting of the pump. This will increase the pressure drop through your valves, and also increase pump flow, hopefully higher than you’re asking of your actuators.
If this doesn’t work, then you may have to reduce the speed of both actuators with flow controls so that combined flow is less than pump flow. If you already have flow controls, this won't be difficult at all. This obviously won’t make your machine any faster, but it will prevent the actuators from slowing when activated simultaneously.
You may also want to research “post pressure compensation,” or just simply “post compensation.” It is a method of using pressure compensators on each work port to enable something called “flow sharing.” It is a technique to allow all actuators to move at a predictable velocity rather than taking the path of least resistance.
Thanks for the question, Raja, and I hope I’ve answered it.