Current Issue Archive Advertise. Power-saving Control In hydraulic systems subject to wide fluctuations in flow and pressure, load-sensing circuits can save substantial amounts of input power Figure 1. Flow-pressure-power Diagrams for Fixed, Variable and Load-sensing Controlled Pumps Peter Rohner Load Sensing Circuit Configuration A load-sensing circuit typically has a variable displacement pump, usually axial-piston design, fitted with a load-sensing controller, and a directional control valve with an integral load-signal gallery Figure 2.
Typical Load-sensing Circuit Schematic The load-signal gallery LS, shown in red is connected to the load-signal port X on the pump controller. Constant Pressure Drop Equals Constant Flow In a load-sensing circuit, the load-induced pressure downstream of the orifice directional valve is fed back to the pump control via the load-signal gallery in the directional control valve.
About the Author Brendan Casey. Brendan Casey has more than 20 years experience in the maintenance, repair and overhaul of mobile and industrial equipment. For more information on reducing the operating cost and increasing the Read More. Related Articles. Understanding Logic Valves in Hydraulic Systems. Featured Videos.
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A load sensing pump has a small control hose connected to its load sensing compensator. This allows changes in working pressure at the actuator connected to the valve bank to be sensed back at the pump. A load sense pump is very similar in function to a pressure compensated pump, with largely the same internal components.
The most important thing to remember about the inside of a load sense pump is that it can change its displacement and outlet pressure precisely for what is needed at the actuator at any operational moment. There is another key component needed for any every load sense pump to work that is not part of the pump itself.
That key is a flow control orifice between the pump outlet hose and the point where the load sense signal is detected. But there must be a pressure differential created across the device. The reason this flow control is so important is because there must be a constant pressure difference between the pump outlet pressure and the load sense pressure.
An advantage of this type of system can be the cost, but the disadvantage will be the efficiency of the pump and potentially fluid cleanliness as described in our article about pairing piston and gear components.
Typically, the flow sharing valves capable of what is described above will require high fluid cleanliness. A pressure filter between the pump and valvebank would not be a bad idea to keep any contamination from the pump from getting to the valve. There is still theoretically a delay, though, while the valve inlet restricts the flow enough to build required pressure when your function requires it. A third method — electronic pump displacement control — is the most cutting-edge technology and seeks to overcome the disadvantages of the hydraulic load sensing pump compensator.
This has been around for years in the closed circuit pump market but is becoming a strong option for open circuits because of the use of electronic controllers that can manage pump flow in relation to the signals it is sending to a valvebank. If a controller sends a signal to a valvebank section that will require 4 gpm, it simultaneously will send a signal to the pump displacement control that results in an additional 4 gpm of pump flow.
No worries about balancing load pressure across spools, expansion in hoses, or competing functions impacting the hydraulic signal. It proactively generates exactly what it already knows the load will require. The challenge here is that a central controller must exist and be programmed correctly.
It can allocate flow and even assign priority electronically to the valve functions in case the pump runs out of available flow.
This is the absolute best method for a crisp response, energy savings, and advanced features such as function priority.
The downsides are cost and initial programming time. Choosing which method is best for your mobile hydraulic system may not be as straightforward as picking the most advanced and highest performing options available. There may be dimensional or mounting constraints that limit you to a small, fixed displacement pump.
This would result in the load sensing valve solution being the most viable. You may already be using a load sensing pump on other projects that can be selected to avoid expanding inventory. That would steer you towards the load sensing pump compensator solution with a simpler valve.
The electronic proportional control may be overkill for your system, but if you have tried other methods with mixed results, then it may be the solution for you. The best solution may even be not to worry about load sensing at all if you have very few functions or if efficiency does not outweigh cost as a design constraint.
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